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Feedback archiveFeedback 2012

Does inbreeding always decrease genetic variety?

Published: 29 April 2012(GMT+10)

E.K. from Sweden writes in response to article What! … no potatoes?:

I have a question on genetic variation.
If a population arises from a few individuals for example you start with two rabbits and then let them reproduce. Do they show an accumulating amount of sicknesses till the point they die off?
Or do the sicknesses over time get weeded out and thus a healthy population result. Are there any observations on that?
Why did not the rabbits in Australia get weakened by inbreeding and were instead so successful?
What happens if you inbreed like that to fast producing animals like fruit flies. Thank you for this site which helps me a lot in making my faith stronger.

CMI’s Dr Don Batten responds:

Dear E.,

The effect of inbreeding depends on several things, including:

  1. The number of genetic defects in the population. This is the most important factor. If organisms do not have any genetic defects, then there is no problem with inbreeding. This would have been the case with the children of Adam and Eve, for example (mutations have caused the accumulation of genetic defects since the Fall in Genesis 3). It would also have been the case with all the animals and plants created in Creation Week (Genesis 1).
  2. The population size. This is the factor that you have focused on. This is not important if the creatures do not have many genetic defects, but becomes more important with more defects. However, it is more a case of having a genetically diverse population, where particular deleterious mutations are not present in all individuals, rather than its size.
  3. The number of offspring possible. Creatures with high breeding potential have more chance of getting rid of deleterious mutations.

The rabbits in Australia are an interesting matter. They have certainly thrived, apparently from a relatively small number introduced in 1859. There were rabbits on the First Fleet (1788) but apparently they did not thrive (maybe they were all eaten as food was in rather short supply in the early days of European settlement). The current population mainly came from the later introduction, although it is not certain that these were the only rabbits introduced. Hares had been brought in earlier (1840?) and became feral and foxes were brought in to control the hares in 1855 (and also for hunting). Clearly both hares and foxes have thrived. There was also a small introduction of sparrows (1863), which have also thrived in Australia.

There is quite a list of troublesome imports into Australia (e.g.: Wikipedia: Invasive species in Australia). It is difficult to find the actual numbers introduced, but there must have been quite small numbers of most of them (except perhaps the cane toad) and they have all thrived.

There are many examples of isolated islands where land animals have colonized, clearly with only a very small number, but the animals have thrived.


Of course with domestic dog breeds, they are all heavily inbred. Some of them are clearly not very healthy because of this (see our articles on about mutant dogs or mutts; see further reading below), but many breeds are quite healthy. Also, the inbreeding does eliminate the lethal deleterious mutations from the population, so it does have a purifying effect, as you have recognized. This inbreeding is done also in plants (maize, for example). Several generations of inbreeding is done and then two inbred lines are crossed. The result is ‘hybrid vigour’ where the seedlings thrive.

So, the evidence would suggest that inbreeding depression is probably overstated as a problem for colonizing the world from animals on the Ark, for example (and remember that the time of the Flood was much closer to the creation, so the number of genetic defects would have been much less than today). Dr Sanford’s work on genetic entropy is relevant to this topic, suggesting a significant accumulation of genetic defects due to mutations since the Flood. See Plant geneticist: ‘Darwinian evolution is impossible’.

I hope this helps.

With kind regards,

Don Batten

Boris K. from Croatia writes:

Dear Sir / Dear Madam,

I have a friend who is finishing his Ph.D. in agriculture (esp. fruit-breeding). I’d like to give him evidences toward creation-based science, and against false evolution-based science. Could you send me some Internet links which I can forward him?
Thank you for your answer in advance!

Dr Don Batten responds:

Dear Boris,

Two of us at CMI have PhDs in agriculture—Dr David Catchpoole and me. I have been involved in fruit breeding and other fruit crop research. You can read my story here: Harvesting real fruit.

According to the measured rate of mutation, the human population cannot have been here for long and is heading for extinction. This is all consistent with the Bible’s history and timescale.

There are many articles about genetics on An interesting one is the interview with Dr John Sanford, a Cornell University genetics professor who invented the gene gun. Dr Sanford also has published an important book that shows how evolution is genetically impossible, due to the high incidence of mutations. According to the measured rate of mutation, the human population cannot have been here for long and is heading for extinction. This is all consistent with the Bible’s history and timescale. The book is titled: Genetic Entropy and the Mystery of the Genome. There is a DVD of a lecture he gave on this topic also (The Mystery of Our Declining Genes DVD).

You might also like to refer your friend to the work of Dr Robert Carter (use the search window). Read an interview with him: Corals, genes and creation, and there is a list of his papers under his cv. You can see a short interview with Dr Carter here: Interview with CMI—US’ lead scientist/speaker Dr. Robert Carter (6 minutes), 2007.

I also suggest the articles under the Genetics Q&A page and the other topics under Biology (such as mutation, speciation, etc.) on the Q&A page.

I hope this helps you help your friend.

Every blessing,

Don Batten

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Readers’ comments
Marc K., Australia, 29 April 2012

Actually, sparrow numbers have taken a dramatic dive in Sydney. When I was growing up you saw flocks of sparrows everywhere. Now it is different - I haven't seen even a single sparrow for, maybe, 20 years. I can't speak about other areas as I don't know if they were ever as numerous 40 years ago as they were in Sydney.

As to the cause, maybe, one of the recent invaders from up north or out west are outbreeding them (or eating their young?).

Speaking of eating, I have seen a few "ucelli" blackboard specials listed in several Italian restaurant here. Italians used to tell me that that is why you no longer see them in Italy - the little birdies were quite a delicacy.

I once worked with a Chinese doctor. She was waiting for her registration here. We took some of our clients to Coogee. While eating some fish and chips we threw a few scraps to the big gulls. She commented that "In China we no longer have gulls." In response to my 'why?' she said,"Because we ate them all!"

Don Batten responds

The arrival of Indian mynas has impacted the populations of many bird species and this could be a factor in the apparent decrease in sparrow numbers.

Denis C., Australia, 3 May 2012

There are plenty of sparrows out in Sydney's West at Penrith and a few Indian Mynas. I did not know that sparrows were introduced.


Geoffrey F., Canada, 4 May 2012

I would not use Wikipedia as a reference as it is not an authoritative source and not recommended in academia. Not to mention its antagonism to creation.

Don Batten responds

We agree that Wikipedia is generally not a good source to cite, for the reasons you give. In addition, articles can be quite changeable/ephemeral. So we have an editorial policy of avoiding Wikipedia. In this case I cited a particular version of a non-controversial article that seemed to be well researched.

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