Did 90% of Animal Species Appear about the Same Time as Human Beings?

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This is a companion discussion topic for the original entry at https://biologos.org/blogs/archive/did-90-of-animal-species-appear-about-the-same-time-as-human-beings

[jpm (Phil McCurdy)]

Good explanation. Also discussed on this thread:

Most species originated at the same time?

I came across this article first on a Christian new site, with headlines and quote mines that distorted the message (https://www.christiandailyreporter.com/ ), which is another interesting subject, but was interested if it was meaningful or not, thought I would throw it out here. Massive Genetic Study Reveals 90 Percent Of Earth’s Animals Appeared At The Same Time | Tech Times It states that many species arose about the same time as humans, about 100- 200 thousand years ago. What is the sign…

[glipsnort (Steve Schaffner)]

I’m not fond of the leap from “most recent mitochondrial ancestor” to “bottleneck”. There was a most recent mtDNA ancestor with or without a bottleneck. That the times of the most recent common ancestors seems similar for a lot of species might be telling us that many of them went through a bottleneck around the same time, or it could be telling us that they have similar effective population sizes, or it could be telling us that the effective population size of mitochondria is limited by natural selection. Since humans fall into this group, and human nuclear genomes show no sign of a major bottleneck in the relevant time period, bottleneck should not be the default explanation. @Joel_Duff

[T_aquaticus]

@glipsnort

I’m not fond of the leap from “most recent mitochondrial ancestor” to “bottleneck”. There was a most recent mtDNA ancestor with or without a bottleneck.

The other potential problem that jumps out at me is relying on a single 600 bp stretch of mitochondrial DNA to give us an accurate picture of population dynamics over the last million years. I tend to agree with the authors that DNA barcoding does appear to be a useful tool for identifying species, but I also have my doubts that it can be useful in mapping past population dynamics.

[DennisVenema]

@glipsnort

I’m not fond of the leap from “most recent mitochondrial ancestor” to “bottleneck”. There was a most recent mtDNA ancestor with or without a bottleneck. That the times of the most recent common ancestors seems similar for a lot of species might be telling us that many of them went through a bottleneck around the same time, or it could be telling us that they have similar effective population sizes, or it could be telling us that the effective population size of mitochondria is limited by natural selection. Since humans fall into this group, and human nuclear genomes show no sign of a major bottleneck in the relevant time period, bottleneck should not be the default explanation.

It’s for this reason that I can’t figure out why people (including the authors) suggest a bottleneck to explain their observations. A more interesting calculation (IMO) would be trying to understand how likely it is for a population (of a given effective size) to maintain mitochondrial diversity over a longer timeframe.

That and equating “last common mitochondrial ancestor” with “beginning of a species” - uh, excuse me?

[Joel_Duff]

I’m in the Canadian hinterlands for the next few days so I’m not checking my mail much. I agree with your assessment here. I meant the bottleneck to be one example of several possible explanation for their data. In chopping down the article it was left that simple example of how some mDNA lineages could be eliminated leaving the last common ancestor much more recent than the species origin. Certainly, no all species, or even most, underwent population bottlenecks but there are many other ways in which mtDNA lineages are sorted over time resulting in many lineages going extinct. So, yes, my article is skewed to that single example to make the main point clear about species vs mtDNA ages. @T_aquaticus @DennisVenema

[skavanagh326 (Steve)]

Why is it surprising that intra species variation of mtDNA is very small? Selection pressure in this critical organelle would presumably be highly intolerant of mutation. I expect it would take many hundreds of thousands of years to show any significant degree of change. Which is of course the timeline we expect for speciation. I would argue that a bottleneck isn’t needed to explain anything, everything in this paper just seems consistent with millenial evolution.
It would be interesting to see results from other areas of mtDNA as well as areas of somatic chromosomes.