To: All Msg #27, Jan2593 11:27AM Subject: Re: Has Macroevolution Occured? In article 1993J


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From: Chris Colby To: All Msg #27, Jan-25-93 11:27AM Subject: Re: Has Macro-evolution Occured? Organization: animal -- coelomate -- deuterostome From: (Chris Colby) Message-ID: <> Newsgroups: In article <> (Russ Paul-Jones) writes: >I'm asking for the observations that make up the fact of >evolution. Evolution (changes in a gene pool) has been observed; so has natural selection (the only mechanism of adaptive evolution). Likewise, speciation has been observed. The most recently documented example I know of is in polychaete worms. (I noticed one poster seemed to think speciation would be really big news; it wasn't. It was a note in the journal _Evolution_, not even a full paper.) Common descent is inferred from several observations: 1.) Evolution occurs 2.) Natural selection occurs 3.) Comparative anatomy -- Groups of organisms are "constructed" using the same "building blocks"; mammalian skeletal features are often used to illustrate this in introductory texts. For example the wing of a bat, flipper of a whale, front paw of a cat and arm of a human are all made from the same bones -- the bones are just scaled differently. 4.) Comparative developmental biology -- Closely related organisms share similar developmental pathways, the differences in develop- ment are most evident at the end. This is, again, usually illustrated using mammalian (or sometimes vertebrate) examples. As organisms evolve, their developmental pathway gets modified. It is easier to modify the end of a developmental pathway than the beginning since changes early on have a cascading effect. Therefore, organisms pass through stages of early development that their ancestors passed through. These stages, however, are modified because selection "sees" all stages of an organisms life cycle. So, an organism's development mimics its ancestors although it doesn't recreate it exactly. 5.) Comparative biochemistry -- closely related organisms have similar genes and proteins. 6.) Biogeography -- Organisms clustered spatially are frequently also clustered phylogenetically; this is especially true of organisms with limited dispersal opportunities. The mammalian fuana of Australia is often cited as an example of this; marsupial mammals fill most of the equivalent niches that placentals fill in other ecosystems. If all organisms descended from a common ancestor, species distribution across the planet would be a function of 1.) site if origination 2.) potential for dispersal and 3.) time since origination. In the case of Australian mammals, their physical separation from sources of placentals means potential niches were filled by a marsupial radiation rather than a placental radiation or invasion. 7.) The fossil record -- Fossils show hard structures of organisms less and less similar to modern organisms as you go down the strata (layers of rocks). In addition, patterns of biogeography apply to fossils as well as extant (living) organisms. When combined with plate tectonics, fossils provide evidence of patterns of distributions and dispersals of organisms. For example, South America had a very distinct marsupial mammalian fauna until the land bridge formed between North and South America. After that marsupials started disappearing and placentals took their place. This is commonly interpreted as the placentals wiping out the marsupials (but this may be an over simplification). 8.) Evidence of "jury-rigged" design -- If all organisms descended from a common ancestor and their phenotypic traits developed over long periods of time due to modification with descent, organisms should show evidence of "jury-rigged" design -- i.e. structures that were modified enough to make do, but could have been designed much better if a mechanism for building the structure from scratch were avail- able. I have a file that lists some of these; I'll try to post it later today or maybe tomorrow. (Someone else has a huge file of this, maybe they will post theirs "hint hint" 8-) Evolution works by diddling with what it has available; as a result of this, suboptimal design abounds in nature. 9.) The nested pattern of biological traits -- This is IMHO, the best evidence for common descent. If organisms share a common ancestor and are modified with descent, derived traits should be distributed across groups of organisms in a nested manner -- traits should not be "mixed and matched". This pattern is seen in comparative anatomy, development and biochemistry. Although this is the best evidence for evolution, it also requires the most knowledge of biology and is sometimes hard to get across to people. This will come up in my discussion with Mr. Johnson, watch that thread for a full explanation. 10.) Current knowledge generates predictions -- In several of the above examples I stated, closely related organisms share X. If I define closely related as sharing X, this is a contentless statement. It does however, provide a prediction. If two organisms share (oh lets say) a similar anatomy (two birds, for ex.), I would then predict that their gene sequences would be more similar than a morphologically distinct organism (like a plant, for ex.). This has been spectacularly borne out by the recent flood of gene sequences -- the correspondence to trees drawn by morphological data is very high (amazingly high, IMHO). The discrepancies are never too great and usually confined to cases where the pattern of relationship was hotly debated. The worst correspondence (although still pretty good) seems to be amongst invertebrate animals (rapid radiations give less time for enough traits to be nested to see a nice pattern, especially since rapid radiations usually involve heavy duty modification.) If you doubt evolution at all, check it out on your own. Read some biology texts (ignore everything that is interpretation -- read it, but don't believe it with out proof) and make up your own mind. Go to the zoo and look at animals. Go to botanical gardens and look at plants. Go to museums and look at fossils. Take notes -- what features do the organisms have, where did they come from, etc. Sit down and think, "If everything came from a common ancestor, what predictions does this make?" and "Does the evidence bear this out?" The great thing about science is, you don't have to listen to anybody's opinion about anything; if you are curious, you can check out the facts and make up your own mind. In my own highly biased opinion, biology is the coolest thing since cheeze whiz. The more you study it, the more realize A.) How diverse and fascinating living organisms are and B.) what an amazingly descriptive and (most importantly) predictive theory evolution is. You had a few other good questions, I'll try to get around to them in a few days. >-Russ Paul-Jones PS I mailed you my FAQ. If you don't get it, email me at the below address and give me an alternate address (I seem to bounce a lot of mail responding to people on the net.) Chris Colby --- email: --- "'My boy,' he said, 'you are descended from a long line of determined, resourceful, microscopic tadpoles--champions every one.'" --Kurt Vonnegut from "Galapagos"


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