Did a “Massive Genetic Study Reveal 90 Percent Of Earth’s Animals Appeared At The Same Time”? No, it didn’t.

The declaration in quotes is the title of an article in Tech Times reporting on a paper published in Human Evolution by Stoeckle and Thaler with the title Why should mitochondria define species? Not surprisingly, young earth creationists and others are linking this article all over the internet. I was first made aware of it by a friend, and then I read the original paper. The following is my analysis of that paper, originally posted in the Facebook group Celebrating Creation by Natural Selection (CCNS).

As expected, the Techtimes article completely misunderstood the original paper. It does not claim that 90% of all animal species began at the same time, 100,000 years ago, and it is in no way supportive of YEC. The paper, which I believe is poorly written and highly speculative, is an attempt to make sense of the fact that mitochondrial DNA bar coding is useful in identifying species. That fact is now consensus, and it derives from the fact that genomic differences between many species (like two worms or two similar insect species) can be quite small, but they are much greater in mt DNA (mt=mitochondria). The reason for this is that mtDNA has a far greater mutation rate than genomic DNA, since negative selection is not an issue (meaning a deleterious mutation in mt will not usually kill the cell in which it lives). So when two species are hard to differentiate by genomic sequence differences, they can be up to 2 or 3% different in their mtDNA. This also implies that there is very little variation of mtDNA within the individuals of any species. The purpose of the paper is to suggest hypotheses as to why the latter observation is true.

One possibility for explaining why mtDNA within a species shows less variation than between closely related species is that a particular species went through a population bottleneck followed by rapid expansion. A bottleneck can occur for several reasons, but generally involves a large decrease in the population, usually due to adverse environmental conditions. It can also result from migrations. Bottlenecks are very common during evolutionary history, as populations deal with all kinds of stressors. Bottlenecks are known to cause severe restrictions in DNA sequence diversity, both in genomes and mt. We know that humans went through a severe bottleneck between 70,000 and 150,000 ya. The authors propose that most other animal species also suffered some form of bottleneck within the past 100,000 or “several hundred thousand” years ago. That is one possible explanation for the relatively low intra-species mtDNA diversity seen in modern animals. Personally, I am not convinced by this explanation, since the genomic DNA diversity data does not seem to match, as far as I know. But even if this explanation is correct, it says nothing about all animals originating at the same time. What it might suggest is a large-scale environmental change (such as the start or end of an ice age) or several such changes affecting different species at different times, which we know happens continuously.

The authors of the original paper never discuss “origin” or beginning of species. They simply suggest that one or more bottlenecks have happened to a large majority of species within a relatively short time frame. While that explanation is far from consensus at the moment, even if it gains evidence, it does nothing to shake any part of evolutionary theory or our knowledge of how environmental change affects population genetics.

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3 Responses to Did a “Massive Genetic Study Reveal 90 Percent Of Earth’s Animals Appeared At The Same Time”? No, it didn’t.

  1. SheilaDeeth says:

    It’s so frustrating that a written misinterpretation of a study gets quoted as reliable fact while any other interpretation becomes just skewed opinion. Thank you for this post.

  2. A few years back, a friend let me borrow a book arguing against new atheism. There was a large section devoted to scientific arguments by intelligent design advocates and the cambrian explosions was brought up as an example of the majority of species arising at once. I haven’t looked into it too much, but isn’t the cambrian explosion just one of several other such instances of a sudden flourishing of life in history? Have there been others along the way?
    Peace to you, friend.

  3. Yes. So called “explosions” (which generally take millions or tens of millions of years) happen after large extinctions, where empty niches are filled more rapidly than otherwise. The Cambrian is somewhat unique in that many new body plans arose in a short time frame. There were of course, other life forms preceding the Cambrian, but they were quite different. Its a puzzle.

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