Hi, this is Professor Steven Secula. I'd like to welcome you to this brief introduction to the concepts of natural selection, creationism, and intelligent design. The reason for recording this lecture is because in class, the recording system didn't actually work, and so the lecture that we did on November 14th was lost, and so this is to make up for that. Because this is important material, it's useful to have something around you can use to supplement and go back to and listen to. And so I hope that this lecture will serve that purpose. So without further ado, let me jump into the lecture. Now the purpose of this lecture is to prepare you in several ways. It's extremely brief. It may seem long, but it can take weeks to really go through this material at the level of depth that I would like to do it. But of course it's a class and we don't have that kind of time. So what this lecture will do is prepare you for the basics of the concepts of evolution, natural selection, creationism, and intelligent design. And then you're going to get a lot of depth into the biology from a lecture by our own Professor John Wise of the SMU Department of Biology. And he's going to give a lecture that he usually entitles something like intelligent design is not science, where he'll talk about some of the scientific sounding claims of intelligent design and how they're easily refuted simply by looking in the natural world. Then we'll follow up with the third lecture, which is a discussion of these lectures in an additional class period. Now this audio recording with slides will actually cover everything that was going to be presented not only on November 14th, but which didn't get finished then and will be continued on the following Monday. Now I want you to keep some critical questions in mind. After all, this is a class on the scientific method in debunking pseudoscience and it's about the scientific method. So you've really got to keep science and the scientific method in mind, because what we're talking about is something that claims to be science when in fact it is not. And it's perfectly fine that it's that other thing, but it's not okay that it tries to be science or claims that it's science when in fact it presents things which are outside the scientific realm. So for instance, things I want you to keep in mind are when an explanation of the natural world is offered, what is the hypothesis? Is that hypothesis testable? What predictions are made by the hypothesis? All the basic stuff about the scientific method. What tests are proposed or can be proposed to assess the predictions of the hypothesis? And most importantly, can the hypothesis be falsified? That is, if a proposition is made to explain observations in the natural world, can that hypothesis actually meet a test where it can be ruled as wrong? That's a critical element of any scientific idea, and surviving those tests repeatedly is what takes you from hypothesis to scientific theory and eventually to things like a law. So with those kinds of questions in mind, let's go ahead and proceed. Now I'm a physicist and so talking about biology, I find wonder in the natural world, but I don't obviously appreciate all the subtleties that a really well-trained research biologist is going to understand, but I would say that if I was as a physicist going to summarize the question that biology is trying to deal with, at least at its heart, it's sort of summarized in this picture right here. And this picture is, I think it's really quite lovely. It's fish, a whale shark, and you can see a person in a scuba gear in a wetsuit up in the top of the slide. And I think this really summarizes a critical fundamental question that biologists are trying to answer about the natural world, and that is, where does all this diversity come from? We have creatures like fish that spend their entire lives beneath the surface of the water. That's the world that they know. They breathe the oxygen out of the water. They live their entire lives down there, blissfully ignorant of the fact that there are creatures roaming around up on a hard surface above the water, out in the air, where they can't survive for very long. Whereas we, as creatures who primarily live on the surface of the earth, but who can also be partially amphibious, and we can swim in the water at least for short periods of time, we can't breathe underwater, we know a different world, and yet we're all sharing the same planet. So the question is, where does this diversity come from? Is it linked? How is it linked? And can we understand that? Now, if we think about scientific explanations, we're talking about observations of the natural world with natural explanations for things we observe in the natural world, because those are the things that are within the realm of science. Science cannot assess the supernatural, because the supernatural may not be repeatable, and one person's supernatural may be very different from another person's supernatural, and therefore that defies objective reality and really doesn't fall within the purview of science. So we're talking about scientific explanations for things like the diversity of the natural world, and we need to ask the question, is there a scientific explanation for the diversity of the natural world? And the answer is yes, and that scientific explanation is the theory of natural selection. Now, it's a scientific theory, and you'll see why as I go through the next few slides, but its goal is to explain evolution. Now, an interesting thing, a lot of people who claim to be opponents of the science will say things like evolution is an opinion or the theory of evolution. The reality is that evolution is a fact. So if you look in the record of the natural world, if you look at fossils, if you look at the natural history of the world, just observe it. You'll see that there's not only diversity in the world, but there has been great change in life over time, even short periods of time. Evolution is merely that change of life with time, and the question is why does that change occur? Where does diversity come from? So evolution is an observed fact of the natural world, things evolve. The explanation for that evolution is the theory of natural selection. That's the scientific explanation for that diversity, for that change. In the time of this young man pictured here, whose name is Charles Darwin, and we're talking about the 19th century here, mid-1800s, the fact that species change over time was not new information. But the question that was perplexing the leading biologists and geologists of his day was the mechanism by which this occurred. Now the popular explanation, especially in England or generally in Europe, was to go with what the Bible said. So the Bible is the founding theological text of Christianity, as well as Judaism, at least the Old Testament. And the instinct was to look there for explanations, because again, the view of religion is that its explanations of the natural world, at least to the faithful, are the right ones, independent of what's actually going on in the natural world. That's certainly one way of looking at it. And it was a prevailing opinion that the literal reading of the Bible and its story of creation was the right explanation. But geologists had long suspected that this wasn't the case, because they were finding all kinds of things in the geological record that didn't really line up very well with the biblical story of the history of the Earth, the natural history of the Earth. But it was really Charles Darwin who took a very famous voyage when he was in his 20s on a ship called the Beagle. He did a five-year voyage around the world, and during that time he turned into a practicing geologist and collected a lot of biological samples on his journey. From that scientific trip around the world, he later, almost two decades later, formulated on the origin of species, which was a very long tome and was the first really well-established scientific explanation for the diversity of life on Earth. And there are really just a few core things that you need to know about the theory of natural selection as an explanation of evolution in the natural world. First of all, the diversity of life is not an accident. This is a misconception about the theory of natural selection. Critics of the theory will say that what it says is that life randomly arises either out of nothing, which is a completely different question of where life actually comes from, but even within an existing system that contains living organisms, that the claim is that evolution just says that life is random and stuff happens randomly. And that's not actually true. The diversity of life as envisioned by the theory of natural selection is certainly not an accident at all. There is something which is random, but it's not this. The outcome is not random. The outcome, that diversity, that change of life over time is due to pressure from the environment on a population of organisms. So those organisms, like a population of rabbits, for instance, they can either adapt to their surroundings or unable to adapt.  Now, what might cause the rabbits to have to adapt to a situation? Well, for instance, there might be a predator in the environment, for instance, a fox or a group of foxes. So the foxes want to eat the rabbits and the rabbits don't want to be eaten. They want to live peacefully and multiply and go on living and raise their kids, and then the kids want to go on multiplying and having kids of their own and so forth. They don't really want to get eaten by the foxes. So the existence of a population of predators that preys on the rabbits puts pressure on that population of rabbits. So they can either adapt to that situation or they can possibly be completely eaten into extinction. Now, adaptation may be conferred by a pre-existing ability. Rabbits can run. The ability to run and especially to dodge and weave and avoid their fox predators would confer the ability to adapt. On the other hand, it could be that the population of rabbits can run, but maybe not all that well, or maybe some can run better than others. And so the selection pressure from the foxes will preferentially kill off the slower rabbits, leaving the faster ones. And it's possible that some of those rabbits that originally were slow as they reproduce and have kids, that there might be random mutations in their genetic sequences as they divide and copy that causes the organism at birth to have an advantage over its peers. I mean, maybe a lighter bone structure that allows it to be more nimble and move more quickly and more flexibly. That might confer survival advantage under selection pressure from a population of foxes. This is called speciation. So when a mutation allows a species to change in such a way that it can avoid the selection pressure that would otherwise threaten to wipe it out, this is adaptation. And that can cause a subpopulation of, say, the rabbits to branch off from the original population and be different, be faster, maybe have different shaped legs or something like that that confers a survival advantage. And this principle is simply called descent with modification. That is, species we see now descended from previous populations of animals with similar traits. But the ones we see now are better adapted to your environment because those that were able to pass on their genes survived to do so. And those that got wiped out by their environment didn't. So they were much less likely to pass on their genes before they died. So this is a core principle of natural selection. And this is by no means random. The fact that foxes want to eat rabbits puts pressure on the rabbits and forces them to either run faster or through a modification of their genes at birth, be faster, and then pass those genes on to their children who will also potentially run faster or get wiped out. So that is not random at all. That's intentional. The predator puts selection pressure on the prey. And so this is the non-random part of natural selection. The random part is where the mutations may come from in the genetic code. Mutation is the only potentially completely random part of natural selection. Chemical changes in the DNA during copying, you know, at the time when an egg is fertilized, for instance, in mammal reproduction, it's possible that a mutation may occur at the genetic level that gives the child some advantage over the parent. And then that child is more likely to survive and pass its genetic change onto its descendants that may or may not happen. It depends on the circumstances. But the actual selection is intentional while the mutation may be random. So if the mutation leads to a beneficial outcome, it won't be random at all that it gets passed on to the next generation if it confers a survival advantage. So this is the essence of natural selection. It explains the diversity of the world in that populations may be descended from prior populations that were much more similar to each other, but now they look very different. And, you know, for instance, a good example is hippopotamuses and whales. So hippopotamuses and whales are actually related creatures. It's just that they shared a common ancestor a long time ago. And I like the analogy that Professor Wise gives on this issue. You need to think about life as you see it on Earth now as a collection of cousins. Now, the cousins are not directly genetically related to one another, but they share a common ancestor, you know, grandparents, for instance. And that's the common ancestor. You look similar to your grandparents, and your cousins may look similar to your grandparents, but your cousins may look very different from you because they resulted from a completely different reproduction cycle than resulted in your grandparents' kids and then you. So that's something to keep in mind. Life, as we see it on Earth now, can be thought of as a family of cousins. And there may be similarities, or some of them may be very different from one another, but the reality is that they shared common ancestors, you know, could be as recently as a thousand years ago, could be a million years ago, could be half a billion years ago, but there was a common ancestor at some point that eventually branched due to selection pressure in the environment. And that's where the diversity of life comes from. Now, a natural question, a critical question to ask at this point, if natural selection is a scientific theory, at its core, it must be falsifiable. So is natural selection falsifiable? And the answer is quite simply, you bet. For instance, the Earth might simply be too young for natural selection to have worked. Natural selection requires time because the changes that build up in a population due to selection pressure, those changes may not happen rapidly. Now, they can. There are examples where it happens in a century. We'll see a movie from the Howard Hughes Medical Institute in class about this. It could happen in a thousand years, could take a million years, could take half a billion years. If the Earth is younger, then the time needed for the diversity of life as we see it now to have occurred through natural selection, the natural selection could be wrong. If we find a fish fossil in a geological layer that dates back to a time before fish appeared, then natural selection is wrong. Another great example that Professor Scalise gives in class is if we were to find a human skeleton inside the mouth of a Tyrannosaurus skeleton and the bones all have the same date. Well, that would suggest that natural selection is wrong because humans and dinosaurs did not live at the same time on Earth. They lived a long time apart. And so finding a human skeleton that dates right back to the age when dinosaurs existed would violate the predictions of natural selection, would be something that can't be explained by natural selection and would potentially disprove natural selection. Another thing that could happen is a new species might spontaneously appear with no relationship to other species. I'm a big fan of homestarrunner.com. I like the cartoons there. And I remember a cartoon Strongbad email where Strongbad talks about the starrence and this creature, the starrence, pops out of his imagination and appears on Earth. And I've depicted it here for fun in the bottom right. If a starrence were to just appear out of nowhere in the biological systems of our world with no genetic relationship to any other species that we know about, well, that might be evidence against natural selection. So this shows you that at any moment, like any good scientific theory, there's a chance you could make an observation that completely disproves the original hypothesis or hypotheses that underline the scientific theory. But in 150 years of testing, despite looking and despite the fact that discovering something like this would lead certainly to a Nobel Prize and lifelong infamy in the scientific community. You'd be famous forever. No one has been able to find a definitive reproducible scientific test, an observation in the natural world that so far disagrees with the predictions of natural selection. Now, interestingly enough, opponents of, for instance, teaching science in the science classroom talking about scientific theories when you teach science in public schools often mistake these fundamental principles of natural selection as a scientific theory for something they're not. So, for example, this is a quote from our own state of Texas here. This is Ken Mercer. He's a representative from San Antonio. He said the following, and he's referring to natural selection, although he's probably talking about evolution, and I'll explain, again, that evolution is a fact, natural selection is the scientific theory that explains it. But what he says is if your theory is right, all these species would get together and form a new species. Then where is the cat dog or the rat cat, whatever it be, they don't come together, cats go with cats and dogs go with dogs. Now, here's my speaker's note. Ironically, as I sort of suggested on the last slide, if there was a rat cat or a cat dog, if we found something like that in the natural world, it would actually be evidence against natural selection as an explanation of evolution because these animals have completely incompatible reproductive systems. So, if you found an animal that was half a rat and half a small cat, that would suggest natural selection was, in fact, wrong. So, ironically, the very thing that Ken Mercer is asking for as proof of natural selection is one of the things that natural selection says that shouldn't happen. So, as a scientific theory, it actually says, well, that shouldn't happen and if it does, I'm wrong and need to be modified. So, what he's asking for is actually evidence against evolution, not evidence for evolution, and I find that sort of quite ironic, at least. It points to the fact that if you're going to be critical of something in the public sphere, you really ought to have a basic working knowledge of what it is and what it is not. Otherwise, you run the risk of embarrassing yourself like this. Now, another critical question you can ask or should ask, does natural selection make testable predictions? And again, the answer is, you bet. Here are some old ones. The earth must be quite old or species would not have had time to develop. Well, given the diversity of life on earth that we see now and the time needed to exert the kinds of evolutionary pressures needed to cause that level of speciation of fish and people, amphibious creatures, flying mammals, it takes a long time and the age of the earth was estimated to be at least millions of years old or older. This was not something that Darwin knew at the time he proposed the theory of natural selection, and so this was a real risk. Proposing that gradual changes over time have created that diversity we see now carries a risk and that risk is that if you then go and independently date the earth and figure out how old it is, you might find out it's quite young and if that's the case, as suggested by the Bible, for instance, as I'll talk about in a bit, then your theory is wrong. But radiological dating, which didn't exist at the time Darwin worked, you can look at the tiny little nuclear clocks that decay inside the heart of certain atoms and by looking at the kinds of nuclear material that's left over in a sample from the earth, you can figure out how long that nuclear clock has been ticking down and pretty accurately date the age of things. And so radiological dating of rocks on earth and even the moon, once we were able to collect samples from the moon, placed the age of the earth at about 4.54 billion years. It's a billion with a B. And that's a prediction that's good to about 50 million years. So give or take 50 million years, that's the age of the earth. So certainly not thousands of years. Certainly not hundreds of thousands of years. Certainly more than millions of years. We're talking billions of years for the earth. So that's a test that natural selection survived. Here's another one. There must be a biological mechanism for passing along traits, heredity. There must be a way that a benefit in a current generation somehow gets passed to the next generation so that it can continue to evade the selection pressure that originally selected for that trait as an adaptive mechanism in the first place. Traits, even dormant ones not expressed in parents or even ancestors, predecessors of the parents must have a way of being passed on and maybe re-emerging in a population later. But that mechanism was completely unknown at the time that Darwin published his work. And it took a long time to really understand this. But Gregor Mendel, who was a monk that was doing studies on pea plants in the mid-1800s discovered the principles of heredity as a mathematical science. He knew that if he bred pea plants that were tall and short there was a probability that was well-defined that the children of those pea plants would have certain ratios of tall plants and short plants. And thus genetics was discovered. Well, a long time, it was nearly a hundred years later that DNA was actually identified as the molecular source of heredity the code, if you will that allows for the making of proteins and other things which then result in the creation of organs and other structures in living organisms that give us the ability to survive in the environment. So DNA was finally established as the molecular mechanism but the mechanism was sort of understood and Gregor Mendel's work was rediscovered after he died but it really didn't have a cause that was known. So again, there was a risk here Darwin was proposing that there must be a mechanism otherwise natural selection can't work as he wrote it down but it survived that prediction. So another one, mass extinctions may be possible when a species or a whole class of species simply can't adapt or don't have time to adapt. So for instance, if a massive swarm of a new predator enters the environment and the organisms can't withstand the onslaught of that number of predators, they may be wiped out or if the climate changes very suddenly either through natural mechanisms or a catastrophic event of some kind that can cause a lot of species to be wiped out because they simply can't adapt. So as an example, let's think about our rabbits again if the climate shifts in such a way that the weather on average drops in temperature over just a period of a few years rabbits that have a longer codifer are much more likely to survive and pass on their genes than rabbits with a short codifer. And so if the population can't adapt quickly enough, if the rabbit fur is simply not thick enough on short enough time scale to be passed on to children and passed on to their children, then it's possible that population of rabbits can be completely wiped out and go extinct. Dinosaurs, another great example, there was a cataclysmic event at the end of the age of the dinosaurs that wiped out most of them although there's plenty of scientific evidence that exists now that some dinosaurs share a common ancestor, have a common ancestor that's related to our birds of today. So birds seem to have descended from common ancestors with dinosaurs, which is fascinating. And finally here's another one. Natural selection would predict that seemingly very different species may have simply branched long ago in the environment, but they really should share some kind of common inheritance information. And again, it boils down to the mechanism of heredity, what's the code that underlies this diversity and the ability to pass information on to your children, so for instance genes. That mechanism this idea that species might be related was sort of obvious in some cases from the fossil record at the time of Darwin, but I don't think he even understood how deeply this was true, and once we understood that DNA and matching up genes in one species DNA to genes in another can tell us how closely they were related when they shared a common ancestor. We've learned that humans and chimpanzees have 99% of their DNA in common, and they shared a common ancestor about 5 million years ago. And that's just stunning. That's how connected we are to the world around us. So tells us the observations of the natural world. Whales and hippopotamuses, as I mentioned earlier, are a fascinating case where they actually have a lot of structures in their bodies that are very similar to one another. You can look at the skeletons of whales and hippopotamuses and immediately see some similarities between them, and genetic testing reveals that in fact those similarities are not an accident. They're as predicted by natural selection a common ancestor at about 50 million or so years ago in the record of life on Earth. Such different creatures, one living on the land happy in the water but bebreeds air. One spending most of its life under the water but needs air occasionally so it comes up to the surface, and yet they're related at a deep level in the past through a common ancestor. I want to close the section of the lecture with a quote. It's one of my favorite quotes, and that quote is by a Russian Orthodox Christian named Theodosius Dubjonsky, who's also a biologist, and in 1973 he wrote an essay, and I'm just going to quote the title because I think the title says it all, and the title is simply nothing in biology makes sense except in the light of evolution. Now I've added seek here, which is Latin. You put that in a quote when maybe you, the user of the quote, disagree with a spelling or something like that in the quote, and I'm going to qualify the here. Why would I put seek next to evolution in here? Well it's what I said earlier. I would say natural selection, not evolution, because evolution is a biological fact that's observed in the natural world, and natural selection is the explanation of that biological fact. So I would have said if I had written the essay, nothing in biology makes sense except in the light of natural selection. Now let me change gears a bit, because the core part of what we want to get into in these lectures has to do with something that wants to be science, that claims that it's science, but in fact is not science, and it doesn't take much scratching on the surface of the claim to reveal that it's not science. It's something else. It's something else, and it can be quite beautiful, but it's not science, and that is creationism. Now creationism doesn't have an easy definition, and the first thing you have to know is if you're going to use mythological or religious creation stories as scientific explanations of the natural world, because science operates on the principle that there's an objective reality that we can all measure and observe, and then come to a common understanding of that natural world, you have to first ask a critical question about using creationist ideas to try to apply them as science, and that is which creation story is correct. That's the first question, because there isn't just one. There have been many cultures on this planet, human cultures through the history of our species, and it's only recently that we started writing things down or illustrating things in such a way that those stories can be communicated, but many cultures across the world and through time have written down or passed on in an oral tradition their creation stories, and so we have a huge list of creation stories available at this link here, and you can go scroll to the bottom of this page and have a look. But this is a problem, right? Because when you say, I'm going to believe creationism is the only explanation of the natural world, independent of any observations, independent of any observations, you first have to state what creationism, because there are many creationist stories that have been made by cultures across time and across the geological world, the geographic world, that have nothing to do with one another, but for those cultures they were the true story of how the world came to be. Absent observations, deep observations of the natural world themselves in many cases. So the question you have to ask first is if you're just going to use creationism as science, you have to first answer the question which one is right, absent any evidence, not just opinion, not just cultural values or beliefs, but evidence. Because that, again, we're talking science here, folks, and that's what you want. You want evidence. Okay, well if you can get past that problem we can at least stop and focus a bit more narrowly on this issue of creationism and we can talk about the United States. Now in the United States, what is often meant by creationism is something which comes from the loudest voices who actively oppose scientific explanations for the natural world. And in the US, we're talking about creationism as applied from the Abrahamic religions. So Christianity, Islam, and Judaism. Primarily Christianity, but there are plenty of examples out of other Abrahamic religions of creationist arguments being made very loudly in the public sphere and particularly as it affects public school science education. Now the problem here again is that there are many different kinds of creationists even within this specific area of religion, Abrahamic religions. And I'll talk about those more in a moment, but some basic tenets of these and again they don't all agree, but here are a few that are sort of common amongst different kinds of creationists. All species were created all at once by God, at least the loudest voices in the creationist movement claim this. And their diversity was the choice of God. There are actually some creationists that would refute the first part of that statement. So again, they can't even agree on the basic statement that they're making about their creationist philosophy. Another tenet is that the earth is only about 6,000 years old maybe up to 10,000. Some of the young earth creationists will allow up to 10, but 6 is a typical number that gets bounced around. And the 6,000 is actually determined a long time ago. It was written down calculated by James Usher using only information from the Bible. It had nothing to do with observations of the geological natural world. This work was done in 1654 and remember Charles Darwin and his contemporaries were wrestling with the geologic record as it was known in the mid-1800s. Now James Usher was the bishop of Armah and what he did was he simply added up the ages of people relative to dates that were written in the Old Testament and the New Testament and calculated the age of the earth, the date of its creation, the creation of the universe. Now, the people that interpret this most literally are really a special subset, a special branch of creationism called young earth creationists and even there it's sort of a very special branch of that. Usher declared that the earth was created by God on Sunday October 23rd, 4004 B.C. and actually it gets even more specific than that. He said 9 in the morning. This is extremely specific as a prediction goes. And of course if you start finding ways to measure the ages of things on earth that prediction could be readily ruled out. So that's another thing that sort of you find in the loudest voices in the movement coming out is that the age of the earth is not really much more than about 6000, maybe 10,000 years old. And again that's all determined from the Bible independent of observations of the natural world. And a final thing that sort of comes out of the loudest voices is humans were specially created by God and they're not related to other species, well sort of. Or they may have been related to other species that are unique in that they may have something called a soul which is not really defined in any testable way and they're created in the image of God. Now these are all fine religious principles because religion is based on faith and faith doesn't require evidence but science require evidence. They're based on one piece of belief and that is that the world is an objective reality that we can all agree on. Once you get past that everything else can be determined from evidence in the natural world. So the one core belief principle of science is that the world has an objective reality that it's not a different reality for every person on the planet. These are fine beliefs for a religious system but as you'll see they're terrible for for science. They don't stand up to tests very quickly and John Wise will go into this in great detail in his lecture. Now as I promised even within creationism in the United States there's a variety and this table nicely lays out the variety that you can find. There are sort of two major camps. There's Old Earth Creationist and Young Earth Creationist movements. Now within the Old Earth Creationists you find about five categories. Now Old Earth Creationists are perfectly happy accepting the geologic record of the Earth that it's four and a half billion years old and so forth. But even there there are fine gradations about levels different degrees of belief. So for instance there's Theistic Evolution. So Theistic Evolution is an Old Earth Creationism that states that evolution by natural processes is the tool that God used to create the diversity of life on Earth. Again a fine religious belief doesn't tell you anything about the natural world because the people that follow Theistic Evolution as a philosophy except all of geology and all of biology unhesitatingly. So really they're just, they can be scientists they accept the record of the natural world and they look at the Bible and they don't interpret it literally. Evolutionary Creationism is another section of Old Earth Creationists and they believe that Adam and Eve are the first spiritually aware humans. But humans could have existed before Adam and Eve but they're the ones who were sort of first touched by God. They're the first ones to become aware of God and have a spiritual connection to God. And again they have no problem accepting all of geology and all of biology as established by scientific methods so no problem there. Then there's Progressive Creationism and there humans were a special creation event so yes humans appeared at some point but that was something that God did himself or herself okay so again no problem we know that humans appeared at some point in the past and again no problem with geology no problem with biology as established by scientific methods. Then there's Day Age Creationism and Day Age Creationists believe that the six days of creation actually were six geological epics against spanning millions and millions of years not days but millions and millions of years even you know billion years in some cases. So they have no problem with geology they accept the record of geological epics through time but they have to get rid of some biology in order to believe this they don't accept all scientific evidence within biology because they believe that those different epics are representative of the creation stories in Genesis from the six days talked about in Genesis 1-1 and the problem there is that we know that life didn't emerge crisply on the boundaries of these geologic periods and so you have to sort of throw out some biology to get to this point. Gap Creationists are the final group of Old Earth Creationists now they believe that there's a four and a half billion year gap between Genesis 1-1 and Genesis 1-2 so they have no problem with the geologic record but again the creation of life was a special event and so they have to throw out at least some biology to get to that conclusion and then there are the Young Earth Creationists and these tend to be the loudest voices in the culture war that the United States seems to find itself in on a ten year cycle there are two kinds of Young Earth Creationists there are Amphilists Amphilists believe that the Earth was created with the appearance of age the appearance of evolution the appearance of stars that are billions of light years away and so it takes billions of years for the light to reach us which means if we're seeing them that they must be billions of years old that God created the basically created the universe to deceive us so they practice science using scientific methods no problem good geology, good biology, scientifically based but their interpretation of what is observed in the natural world is that it was merely meant to look that way so you can take a negative opinion of why a deity would do that or you can take a positive opinion of why a deity would do that it's your opinion but that's what they believe and then finally there are the Young Earth Fundamentalists and again these really are the loudest voices in the culture war over science and the way science is structured and taught in the public schools Young Earth Fundamentalists take a completely literal reading of the Bible they believe that the word of the Bible is the truth and that everything else must conform to that truth so they have to throw out pretty much all of geology and all of biology based on scientific methods and invent their own versions of natural sciences to explain the Earth's age as being about 6000 years old I'd really like to thank my web colleague Brian Dunning who runs the Skeptoid site and podcast this is a really nice classification that he has and I've taken this from his site and I'd like to give him credit for this now in the United States we have a governing document the U.S. Constitution and that document has amendments to it and the first amendment contains a clause which is known as the separation clause is in the Constitution so that no religion can establish itself as a government and the government can't tell religions which ones are better than others it can't give an advantage to one religion over another and this was in part intended to do away with some of the state and religion ills that the United States as it emerged as a nation had seen in European nations where many of the people that lived in the United States had come from so we have this legal tradition in the United States of confronting issues of science and religion in the science classroom that it's derived from the first amendment of the U.S. Constitution so go ahead and take a look at the first amendment of the Constitution there really is a clause in there that deals with government and religion it's not a myth some people claim that it is the literal wording in the Constitution it's there it's often called separation of church and state and while that literal wording isn't used there's certainly a recognition in the Constitution that religions should never impose themselves on the people as a government and the government should never pick winners in religion now let me talk a little bit about the U.S. legal history of creationism as a scientific teaching in public schools the first famous case is in 1925 is long after Charles Darwin published on the origin of species and certainly long after his ideas started to become useful tools to the scientific community to understand the natural world so at the point of this trial that I'll talk about here the theory of natural selection had withstood multiple tests including the age test for the earth and it really had been shown to be an effective scientific theory something that could explain the natural world make predictions about the natural world and allow for tests after test after test after test of the original hypothesis and new knowledge was created from it it was useful as any good idea in science actually is in 1925 we have this famous case the state of Tennessee versus John Thomas Scopes this was the first legal test of the teaching of evolution in U.S. public schools so at the time for instance in Tennessee it was illegal for a school science teacher to talk about the theory of natural selection and evolution as science it violated something called the Butler Act in Tennessee so science classes talking about biology if they were talking about diversity of life on earth they talked about creation from the Christian sense of creation so Genesis 1-1 and Genesis 1-2 John Scopes was found guilty of violating the Butler Act of Tennessee he was not successful it was a very famous trial there were very famous people involved you can go read books on it it's wonderful he lost which a lot of people don't seem to know but he lost and that established in Tennessee that the teaching of evolution was illegal in state funded schools private schools could teach it if they wanted to but in public schools it was not allowed according to the Butler Act which was upheld by this case so it wasn't really until 1968 when we have the first U.S. Supreme Court decision that really challenges things like the Butler Act you have Eprison v. Arkansas and this is a U.S. Supreme Court decision that returns in Arkansas law that prohibited the teaching of evolution in state funded schools public schools the court ruled that the first amendment of the U.S. Constitution prohibits a state from tailoring education to suit the desires of a specific religious sect or dogma again we're talking about the preventing the government from establishing winners and losers in religion and since creationism is derived from Christian theology specifically certain parts of the Bible religious dogma it comes from a specific religious sect within Christianity that literal reading of the Bible and therefore it would be from a public school teaching that as science that would be imposing a winning religion on a group of people and so scientific explanations were okay but religious ones were not and this was really the first U.S. Supreme Court case law now folks involved in the creationism movement didn't stop there they saw an opportunity and what they did was they tried to recouch Christian creationist theology as science they even renamed it creation science and they started writing books and publishing books that claim that the geologic record could be explained by the Noah flood and actually there's plenty of literature on that you can see why that doesn't work out very well and so the creation science curriculum got developed by by independent people on the court side of the scientific community and then it was ejected into public schools in some states as science and in 1987 we have the case Edwards v. Aguilar and this was again a U.S. Supreme Court decision and it found that a Louisiana law requiring that creation science be taught alongside the natural selection evolution violates the separation clause of the first amendment of the U.S. Constitution there's that separation clause again since the Louisiana law advances a specific religious sect or dogma and it is therefore a violation of the U.S. Constitution to teach that as science in the science classroom comparative religion class not a problem you can compare different religions that's not a violation of the separation clause as long as it's a comparison and not a advancement of a specific religion over another period of time it's not a problem it's not a problem it's a advancement of a specific religion over another using public money in a public school now this then led the way toward something called intelligent design and which is now called intelligent design creationism intelligent design is a further modification of creation science the problem with creation science is that it's still talking about God it is talking about special creation humans being created differently from other species a tinkering God that goes in and messes with genetic code and makes the diversity of life that we see now but intelligent design does something new it tries to hide the word God and replaces it with intelligent design and if you want to see something funny there's a trial that I'll mention in a moment and that in that trial documents were shown where a book on creation science was you know opened in a word processor a search and replace was done for a specific phrase and intelligent design was inserted in the place of old creation science and in fact this led to copy and paste errors so you can actually see the book evolve from a creation science book to an intelligent design book with very little other changes to the text so nothing was really done to change the underlying arguments it was simply relabeled and in this case by bad copy and paste mistake in a word processor and that was actually evidence used in a court case that I'll talk about in a moment now some basic tenets of intelligent design is that some are all species were designed by an intelligent designer but the designer is not named although you'll see actually that the proponents of intelligent design do name the designer they just claim that they don't name the designer you could say well maybe it's possible right maybe human beings were specially created by a race of aliens that came from another planet tinkered with the genetics of some ape on earth and here we are okay well that's a fine hypothesis but then you still have to ask where the aliens come from because they're intelligent and maybe they're just as special as humans and so you kind of find yourself right back to the original question of well who's the intelligent designer that's a fundamental critical question because that's the theory upon the hypothesis upon which the whole thing is based and they avoid the question when this comes up but that's the tenet that there's an intelligent designer that tinkers with genetic sequences and makes the diversity of life happen in some or all cases the other claims that evidence of this design is detectable by the principle of irreducible complexity and that this claims that a biological structure can exist that's so complex it could not have happened by selection pressure on a biological organism and there are many popular examples and Professor Weiss will talk about some of them and you can see that science scientific research has been done and it decimates this claim because this claim is akin to saying it's so complex I can't understand it I give up and giving up is unacceptable in science if you want to give up then you're not doing science anymore and you can go away and do something else but if you want to do science you need to dig deep into hard questions you need to challenge the understanding of the data and you need to really dig in there and get your hands dirty that's what I don't give up popular examples are the I too complex they claim to have evolved the bacterium flagellum that's the little whip like motor that some bacterium like E. coli used to get around again they claim that's too complex to have happened by natural selection the immune system and again Professor Weiss will talk about these in some detail and you'll see that there's tons and tons of scientific evidence for where these systems came from and what their predecessors look like and how they function more simply and differently this is a crazy idea that that these things for instance can't have natural explanations they also claim that this complexity allegedly can mathematically be defined and experimentally measured although the one or two papers that have been written on the mathematics underline irreducible complexity have been decimated by mathematicians and statisticians this principle is not new it was originally expressed by a philosopher in the late 1700s named William Paley and he wrote a very forceful argument for intelligent design although it wasn't called that at the time and that argument was the watchmaker argument and he reasoned that if the biological world is like a field and you're walking through the field and you trip on something and you look down to see what you've tripped on and you see a rock then in your mind you think well that rock could have easily been carried there by water or ice or glacial action there's a perfectly natural reason for that rock to be there but if you trip and you look down and you see a pocket watch lying on the ground and you pick it up and you look at it you would say to yourself there's no way that this pocket watch got here it's too complex if you take any of its parts out it doesn't function as a watch anymore so goes the argument and therefore it must have been designed by an intelligent agent and so if you find complex structures in nature so Paley would argue they must be evidence of intelligent design on the other hand we also have tons of scientific evidence that complexity can emerge very easily out of simplicity especially if there's enough time that passes between the simple structures and the more complex ones so this is actually readily decimated within scientific investigation this idea the watchmaker idea was recently renamed by Michael Beehe who's a professor of biochemistry at Lehigh University and a fellow at the Discovery Institute which I'll talk about more later now what are the origins of the intelligent design creationist movement their origins date back to late 1990s although they really emerged in that decade after the US Supreme Court case that found the Louisiana law was a violation of the First Amendment so the movement has its foundations in a document a paper known as the wedge document and it originated from a think tank called the Discovery Institute which is based in Seattle it has another name which is a little more ominous and that name is the center for the renewal of science and culture it's since renamed itself in the last decade so that sounds less ominous but that's its original name and in part the document which is a strategy for how they're going to basically inject supernatural explanations into the science classroom and into science in general I quote directly from the wedge document the proposition that human beings are created in the image of God is one of the bedrock principles on which western civilization was built the cultural consequences of the rise of the triumph of materialism were devastating materialists denied the existence of objective moral standards the Discovery Institute Center for the renewal of science and culture seeks nothing less than the overthrow of materialism and its cultural legacies from the wedge written by the Discovery Institute in 1999 now I'll tell you this if this was a proposal and it was submitted to a funding agency if it was a scientific proposal you wouldn't see the stated aims of that scientific proposal being the overthrow of materialism and cultural legacies so basically cultural revolution scientists don't give a damn about cultural revolution they care deeply about the natural world and why it is the way it is and how it got that way and where it's going but they don't really care about changing cultures they do care about good science being taught in the science classroom that's what they care deeply about you can do whatever you want in the church you can do whatever you want in the state but if you're going to talk about science and you better talk about science and not something else so this right here clearly clearly states that the intelligent design movement is not a scientific movement it's a cultural movement it's a political movement it's a social movement but at its heart it is not a scientific movement and you can go and find copies of the wedge document it wasn't supposed to be leaked but it was leaked and it's all over the web you can find copies of it everywhere and the Discovery Institute is never denied that it's theirs now how do they plan to achieve this well according to the wedge strategy they say the following their goal and again this wedge idea is a metaphor their goal is to drive a wedge between science and society and split the log to tear those two things apart and they will do this in three phases phase one they will conduct efforts at scientific discourse and publication to get their ideas into the science literature now as a comment on this you'll see that this has largely failed because it's not science it's not a good idea it doesn't produce new knowledge and it doesn't explain anything that isn't already explained by natural causes and again John Weiss is going to give you a lot of depth on this in his lecture phase two publicity and opinion making this is an ongoing phase that's my comment that's probably also their comment as well but their goal is to get laws changed in their favor sway public opinion against science and so forth and this is just a summary of their words go look at the wedge document I find it to be terrifying as a scientist phase three cultural renewal and confrontation as if it wasn't creepy enough already they intend to completely change the culture through their efforts again cultural revolution is their ultimate goal they want to change science they want to change teaching and then they want to go after the social sciences in the humanity so all you English professors out there who think you're immune to this you're not their goal is to come for you once they've decimated science now how has phase one gone phase one is supposed to be scientific discourse getting their ideas into the scientific literature so that it can be viewed as equal to the ideas of natural selection where there are tens of thousands I'm probably underestimating that but hundreds of thousands of published papers that use natural selection or test natural selection and have made great strides in our in our societies so I did an exercise I searched on smu.edu slash c u l the central university library search engine here for published works including books newspapers articles and of course peer reviewed journals and scientific articles and I put in the search term intelligent design in quotes because after all that's their core idea and that's if they're really publishing serious scientific papers about this they shouldn't have to hide it so I put that in as a search term with the quotes there so that those words are grouped and I limited to scholarly publications and journals with peer review excluding newspaper articles and theses I restricted topics that this search could be connected to to biology science and then the search engine helpfully offered me intelligent design as a possible option for further narrowing my search and I gladly accepted it because after all why would that keyword be omitted if they were publishing serious papers on this I got 11 results now interestingly as I pick through the results I found only one of them is really what anyone would call a scientific paper the rest are maybe articles and journals but there are articles about social study or commentary on the culture war issues that are associated with religion trying to be covered up as science and taught as science so the one paper that is a scientific paper is actually a scientific criticism of intelligent design and shows how it can be ruled out with data so here's the paper right here testing fundamental evolutionary hypotheses which based on the title I thought could go either way it's in the journal of theoretical biology here's the volume number and the issue and so forth the pages you can go read it here's a great long quote from it consider photosynthetic enzymes from plants living in a hot dry desert a cactus and a desert grass with those from moist temperate grass a wise creator might design similar photosynthetic enzymes for leaves functioning under hot dry conditions the cactus and the desert grass this brings together enzymes from similar physical environments under stress from high temperatures and water deficits in contrast the theory of descent natural selection predicts that the grass enzymes would be more similar this unites sequences sharing a more recent common ancestor irrespective of their current physical environment in practice common and ancestry gives the correct prediction for photosynthetic enzymes the theory of descent leads to testable predictions it is possible for intelligent design to fudge predictions to make them identical to the theory of descent un-satisfactory it provides no mechanism that leads to the observed data and it leads to a creator appearing to be the great deceiver who deliberately misleads rational humans end of quote and here's my own commentary I'm not a big fan of God as a great deceiver that's not my God I'm a theist and that's certainly not the God that I believe in now I don't care what God you believe in you may believe differently and I'm not going to impose my religious viewpoint on you but if God has to be deceptive in order to make the world look like a bi-natural selection I'm a little bit worried about what kind of malicious spirits up there in the sky alright so I think their scientific point is very good so you might claim that intelligent design would predict that in a desert climate a cactus and a desert grass would be much more similar than desert grass and grass from a moisture climate but in fact the grasses are more similar than the desert grasses to the cactus and that suggests the common ancestor is in the past of the grasses not as closely as the common ancestor between the grass and the cactus the prediction of natural selection would be the grasses are more closely related than the grass is to the cactus now in order to understand the intelligent design creation is a movement you need to understand a little bit about some of the people that are very active in the movement that founded the movement and I've mentioned some of them already so here's Michael Beehe who I mentioned earlier professor of biochemistry at Lehigh University and fellow at the Discovery Institute he's very famous now for having appeared in a federal court case in Pennsylvania that I'll talk about in a moment and testified as an expert witness on behalf of intelligent design and well you'll see some of his own quotes later but he grossly embarrassed himself and the scientific claims of this movement in court and again like many of the proponents in this movement do reveal that it's anything but science then there's Stephen C. Meyer who holds a Ph.D. in philosophy and he's the director of the Discovery Institute the renewal of science and culture and a senior fellow at the Discovery Institute Philip Johnson is a retired Berkeley law professor and he's known as the father of the intelligent design movement he's the co-founder of the Discovery Institute and he's credited as a founder of the WEDG strategy that I mentioned earlier and then there's William Demsky he holds many degrees actually he has a bachelor of arts in psychology he has masters in statistics mathematics and philosophy and he holds Ph.D.s in mathematics and philosophy and he's a divinity in theology and he's a senior fellow at the Discovery Institute now one of the things I want you to note is these are some of the leading voices in the intelligent design movement and not a single one of them has credentials in biology Michael B. he is the one that comes closest he's a biochemist now you might think that that's cherry picking and you'd be right I mean I am quoting people here that are leading voices there may be other voices within the movement and some of them are in fact biologists but the reality is that most biologists are the design proponents and so no matter how many biologists they trout out it will never be the same number as the number of biologists publishing things on the theory of natural selection and they're publishing because that idea is successful and the reason that there are no peer reviewed papers using intelligent design to explain the natural world is because it's unsuccessful now the first legal test of teaching intelligent design and creationism in public schools where all these legal issues always seem to come to a head was in 2005 and this is a famous trial known as Kitzmiller v Dover Area School District now in this trial 11 parents sued the Dover Pennsylvania School District for requiring that intelligent design now known as intelligent design creationism be taught alongside evolution in fact as Professor Weiss likes to say he recounts the story that originally the teachers were asked to teach it in the classroom they refused on for at least a couple of reasons one of which was because they can't there's no accreditation in intelligent design and they have to be certified in order to teach something in the public school system in Pennsylvania and in addition they take an oath in Pennsylvania that they won't knowingly lie in the classroom they won't teach something they know is wrong and they claim that this would violate that oath because they know that this is not science so instead an administrator was asked to come into the classrooms and simply read a disclaimer at the beginning of biology class using statements like natural selection evolution are only a theory and of course you know from taking this class you're smart you're an intelligent human being you know that a theory in science is very powerful a theory in fact is often more powerful than a fact because it explains facts so basically these 11 parents decided to sue as John Weiss likes to say what you do in the United States when you don't get your way so the Pennsylvania Supreme Court it was a very interesting trial you can go read the transcripts you can read Judge Jones' summary of his decision in the trial it's fascinating reading and basically Judge Jones ruled that intelligent design is in fact a form of creationism which is why it's now labeled intelligent design creationism and thus it's in violation of previous Supreme Court rulings the teaching of intelligent design in a state-funded school is thus a violation of the First Amendment of the U.S. Constitution now you should note that Judge E. Jones III for the trial was actually appointed in 2002 by President George W. Bush and he was a conservative justice so what I'd like to take away from this is that a person is smart and a person who thinks carefully about these issues and really considers what science is and what science is not is going to arrive at a conclusion that intelligent design is not science regardless of their political philosophies or political background or the reason even why they were appointed to that position in the first place and see that science and knowledge transcends political viewpoint now you might ask what are the current intelligent design legal efforts so they fail to get intelligent design taught as science in the school and so what the intelligent design movement has been doing since this trial is trying to get something called academic freedom laws passed and specifically they're trying to get them passed for grade school so K-12 education in public school systems multiple states have tried to pass them for instance Alabama, Maryland, New Mexico Florida, Michigan, South Carolina Iowa, Indiana, Tennessee, New Hampshire and Oklahoma only Louisiana has succeeded now what is an academic freedom law well they're based on language crafted by the Discovery Institute and they basically ask they state that teachers should have the freedom to introduce alternative scientific ideas or alternative ideas in the science classroom to very specific things like natural selection so biology or climate science climate change, global warming but not to physics, not to chemistry not to earth science not the things that don't feel threatened by only the things that the Discovery Institute feels threatened by and so the language is crafted very carefully so that it doesn't get itself in trouble with the First Amendment but it's also trying to solve a problem that doesn't exist the reality is the public grade school teachers are already free to teach within the constraints of the approved curriculum but that's the keyword approved curriculum so what in general this is viewed as is merely an attempt to open the door to teaching pseudo-science as science so a teacher can get up and start talking off the cuff about their religious viewpoint to the classroom talking about it as if it's science and this completely undoes the process of teaching science to a new generation of students religion is fine in the churches it's fine in a comparative religion context in a class that compares major world religions is not fine as science because religion is not scientific it doesn't require evidence to make progress Indiana incidentally is now the latest state whose legislature is trying to introduce such a bill keep an eye on Indiana and I suspect that more are likely to follow now you don't have to take my word for it you can listen to the founders and proponents of the intelligent design movement and see what they say about what they do and you'll see that they very often say that what they do is not science so here's some of their own words quote intelligent design is just the most theology of john's gospel restated in the idiom of information theory unquote William Dempsky signs of intelligence now I mentioned William Dempsky earlier he's one of the big proponents of intelligent design and a major player in the intelligent design movement through the 90s in the the 2000s and here he's laying it right out so john's gospel is New Testament biblical theology and he's saying that that's just what has been restated into some mathematical language to make it sound like science that's what he's saying quote the conceptual soundness of a scientific theory cannot be maintained apart from Christ unquote again William Dempsky intelligent design the bridge between science and theology so he's unabashedly saying right there that it's Christian theology and Christians theology comes first scientific theory must follow from it and that's not how science operates science operates from observations of the natural world and evidence it doesn't operate from a theological viewpoint science science religion is religion and the two do a great to service to one another when they try to mask themselves as one another quote as a Christian man yes I do believe God is it is God is the divine power and as the intelligent designer of evolution unquote again William Dempsky Darwin's unpaid debt at Baylor University in 2008 at least we have here a quote where the name of the intelligent designer is given directly and again it's a Christianity it's the Christian God quote our strategy has been to change the subject a bit so that we can get the issue of intelligent design which really means the reality of God before the academic world and into the schools unquote Philip Johnson the father of the intelligent design movement on American Family Radio in 2003 quote there are no peer reviewed articles by anyone advocating for intelligent design supported by pertin and experiments or calculations which provide detailed regular accounts of how intelligent design of any biological system occurred that's from Michael B. He in 2005 quote father's words my studies and my prayers convince me that I should devote my life to destroying Darwinism just as many of my fellow unificationists had already devoted their lives to destroying Marxism unquote Jonathan Wells Darwinism why I went for a second PhD and here you can clearly see we're talking about a political movement a social movement this person views science as an ism as something no different from a political philosophy like Marxism and therefore just as worthy of destruction from his perspective that's a social statement that's a value statement that's a political statement that's not a scientific statement if a scientific idea works then it's good if it doesn't work then you throw it out that's how science operates incidentally the person whom Wells calls father is Sun Young Moon father of the unification church which is also known as the Mooneys and also the founder of the ultra conservative Washington Times quote many states have brought in intelligent design but they have called it science a design needs a designer which is God it's religion not science unquote this is William Knowers one of the founders of creation and evolution studies ministry and author of a book called creation evolution and a nation in distress and I find this remarkable candor surprising honesty about the goals of intelligent design creationism and its proponents and incidentally at the time this quote was was made his ministry was making an effort to put religion in science classes in Virginia now this is a quote taken out of the transcript from the Kitzmiller V Dover area school district and you'll find this amusing because we've already talked about astrology in class in the context of whether or not it's a testable scientific idea and of course we found it it's not so here's the reference in the transcript and you have Eric Rothschild quoted as saying but you are clear under your definition the definition that sweeps in intelligent design astrology is also a scientific theory correct Michael B. yes that's correct now I've had some quotes here and I want to close with a quote from our own professor Mark Chansey the Discovery Institute was invited by a student religious organization in 2010 to come and give a lecture and that lecture sounded scientific but of course it wasn't invited by any science department on the campus and in fact the science departments were largely left out well they were completely left out of the planning of the event and largely left out of even the occurrence of the event until the date of its occurrence approached and so there was a flurry of op-eds published in the SMU daily campus after the event from a bunch of science professors at SMU then a response from the Discovery Institute and then there was a response from professor Mark Chansey and at the time he was the chair of SMU's religious studies department not a scientist but somebody who understands that religion is religion and science is science and that mixing the two does a disservice to both and so here's his quote quote many religious groups Christian and other do not regard evolutionary theory as a threat for many people of faith science and religion go hand in hand when scholars criticize intelligent design ID they are not attacking religion they are only asking ID proponents to be transparent in their agenda accurate about their representations of scholarship and willing to play by the same rules of peer review and quality control that legitimate scholars and scientists around the world follow every day unquote and I got to say I can't say it better and then thanks to professor Mark Chansey for saying this so well and so passionately in this response and it's true as a scientist I have great respect for religion and for people of faith but as a scientist and as a person of faith myself I also know that those two spheres of life are based on radically different things faith requires no proof it requires no evidence science demands evidence and it demands proof and mixing the two forcing them to overlap does a great to service to both pseudo science and pseudo religion result your faith should never be based on things that can be decimated by the next experiment and your science should never be based on things that can't be decimated by the next experiment and that's what I want you to take away from these lectures this is a movement a political movement a social movement a cultural movement intelligent design as science creationism as science they're fine in their religious spheres but they're terrible in the scientific world and the only way the proponents of these ideas are going to get their ideas taught as science is to completely change the definition of science as you've seen from the wedge document and as you've heard from Michael B. he's own testimony at the Kits Miller Vidover area school district trial so keep asking critical questions think deeply about claims that people make because something can sound like science but when you scratch away the paint on the surface you may find that it's hollow it's transparent underneath thank you very much


So in this video we are going to talk about ideal and non-ideal solutions. Now basically liquid solutions or liquid-liquid solutions can be categorized into ideal and non-ideal solutions depending on whether they follow or obey Raoult's law or not. Now those solutions that obey Raoult's law over an entire range of concentration are known as ideal solutions and those that do not obey Raoult's law are known as non-ideal solutions. Okay that's all right for definition but what do we actually mean by that? You see if a binary liquid solution is made of two liquids let's say one is A and the other one is B then we know that in their pure components we have AA type of interactions in the liquid A and BB type of interactions in liquid B right and when we prepare a binary solution by mixing these two the resulting solution is ideal if all the type of interactions in that mixture are similar in nature that means the intermolecular attractive forces between AA type of molecules and BB type of molecules are almost equal to those between A and B that is all of these interactions are nearly similar and when that happens we have an ideal solution and if you think this is too idealistic you're not really wrong because a perfectly ideal solution is very rare indeed but that does not mean that we cannot achieve near similar behavior for example a solution of n-hexane and n-hyptane form an almost ideal solution now if you look at a structure of n-hexane it is and n-hyptane would be both are non-polar hydrocarbons and interact with each other through London dispersion forces and when we mix these two together the energy required to separate the n-hexane molecules from each other or the n-hyptane molecules from each other is almost similar to the energy released when n-hexane and n-hyptane interact with each other so what does this mean this means that when we mix these two liquids together the energy of the system does not change drastically and this is why for an ideal solution the enthalpy of mixing would be zero so this means that no heat is absorbed or released when these two liquid components are mixed together and similarly the volume of mixing is also zero the volume of the solution is exactly equal to the sum of the volumes of the two components before they were mixed now this is because you can see from this structure that they're very similar so it is almost like you don't see a different molecule or a different liquid there they are so similar in this structure that one liquid molecule can substitute for the other or fill in the space between the molecules of the other and as a result there's no increase in volume when the two liquids are mixed so these are again the characteristics of ideal solutions another example is benzene and toluene so here again when we mix these two together we get an ideal solution such that the interaction between benzene-benzene molecules and toluene-toluene molecules would be similar to those between benzene and toluene molecules now non-ideal solutions are those that do not obey Raoult's law over the entire range of concentration in such a non-ideal solution the enthalpy of mixing is not zero and similarly the volume of mixing is also not zero now in the case of non-ideal solution the vapor pressure of the solution is either greater than or less than that predicted by the Raoult's law now when the observed vapor pressure is greater than that predicted by the Raoult's law we get positive deviation and when the observed vapor pressure is less than that predicted by the Raoult's law then we get negative deviation so let's understand what we mean by these deviations positive and negative deviations at a molecular level suppose you have a binary liquid solution and let's say it's a close container and A is one type of liquid and B is the other type of liquid let's assume A is a solute and B is the solvent now in the case of a non-ideal solution or specifically the solution that exhibits positive deviation vapor pressure of the solution here is higher than that predicted by the Raoult's law now what type of interaction should happen in the liquid solution so that the vapor pressure of the solution is high so this means that the interactions between these two liquids A and B should be weaker than those between each other that is AA type interaction and BB type interaction are stronger than AB type interaction in other words the intermolecular attractive forces between the solute and the solvent molecules are weaker than those between the solute solute and the solvent solvent molecules for example let's assume that a solvent B is ethanol and our solute A is acetone now if we had only ethanol then the ethanol molecules would associate with each other through hydrogen bonding for example ethanol CH3 CH2 OH right the oxygen atom here can interact with the hydrogen of another ethanol molecule and similarly the hydrogen can interact with the oxygen of another ethanol molecule and so on so you can see that in pure state the ethanol molecules are strongly bonded to each other through hydrogen bonding so that means these molecules do not want to leave each other and go into the vapor state now wait a minute what do you think happens when you add a small amount of acetone to this ethanol some of these acetone molecules will break the hydrogen bonding between the ethanol molecules such that these molecules are now free to escape into the vapor state so because it is easier for the molecules of acetone or ethanol to now escape into the vapor state than when they are in their pure state the vapor pressure of the solution increases and as a result we observe positive deviation now another example of an ideal solution that exhibits positive deviation is a mixture of carbon disulfide added to acetone now what do you think happens in negative deviation exactly the opposite in case of negative deviations from Raoult's law the intermolecular attractive forces between A, A and B, B would be weaker than those between A, B so in this case the liquid molecules are happy to stay connected and bonded with each other and are not in hurry to move or escape into the gaseous phase they're pretty contented and happy in their solution phase now in this case because the individual molecules of A and B are not willing or not interested to move to gaseous phase the vapor pressure of the solution consequently decreases now when does this happen this happens when there is strong interaction between the solute and solvent molecules so let's look at an example of such a solution let's say A is chloroform and B is acetone now when these two liquids are mixed together they result in negative deviation so this is because the chloroform molecules can form hydrogen bonds with the acetone molecules so that looks something like this CH3 CO CH3 CHCl3 so here the electronegative oxygen atom forms hydrogen bonds with the acidic hydrogen of chloroform now the hydrogen here is acidic because the alpha carbon that it is attached to is further attached to three highly electronegative chlorine atoms so these chlorine atoms draw electron density towards itself and that makes this hydrogen atom highly acidic in nature so this strong hydrogen bonding decreases the escaping tendency of these molecules and as a result of that the vapor pressure of the solution decreases and it gives a negative deviation from Raoult's law another example of a binary solution that gives negative deviation is phenol which is C6H5 OH and aniline which is C6H5 NH2 in this case the intermolecular hydrogen bonding occurs between nitrogen and hydrogen of the phenolic OH group so this interaction between the nitrogen and the hydrogen of the OH group is much stronger than their individual AA or BB type of interaction and as a result the vapor pressure of the solution decreases and it exhibits a negative deviation so from here we can get a qualitative sense of what type of molecules can give which type of deviation when they form a non-ideal solution