Most species originated at the same time?


(Phil) #1

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.
http://www.techtimes.com/articles/228798/20180530/massive-genetic-study-reveals-90-percent-of-earth-s-animals-appeared-at-the-same-time.htm

It states that many species arose about the same time as humans, about 100- 200 thousand years ago. What is the significance of that, I wonder?


Did 90% of Animal Species Appear about the Same Time as Human Beings?
(Phil) #2

Here is the link to the original article. While I am most interested in what the original article means, and for someone not involved in research, the significance is difficult for me to grasp, it is also quite interesting to see the evolution of original article-news story-christian news story- and probably will eventually get to the YEC and ID pages next.

I finally got the time to read through the above article, and it is worth the time. Good stuff, at least from my perspective.


(George Brooks) #3

@jpm

So, let’s imagine doing this kind of analysis, starting with all the animals we can look at today, right now.

If we start ticking the Genetic Clocks back into history, we are looking for when 2 (or 3 or a dozen) cousin “branches” of existing species merge into a common ancestral population.

What this is telling me is that 100,000 to 200,000 years ago, very broad ecological shifts, and even shifts in geographical territories, were “hitting” existing populations hard … and thus creating the necessary changes in selection pressures needed to “expose” the sudden value of other adaptations!

150,000 years ago, all the existing populations had their baggage of variant alleles - - in a genetic “come as you are” party! Some populations had a lot of them, and some didn’t have as many. We know that every time a population becomes environmentally stressed, it exposes the hidden value of all sorts of configurations of alleles - - and configurations of alleles - - that never really mattered before.

So… what might do that? Well, for 800,000 years, Earth has been globally subjected to Ice Ages - - pretty much one every 100,000 years!

This makes good sense, yes?

Only surviving populations are available to analyze. So I can only surmise that each one of these Ice Ages created its own batch of “new surviving” populations.

And from these new populations created anywhere from 800,000 to 300,000 years ago, the most recent ice ages (100,000 or 200,000 years ago) produced the “spanking new” populations with genes we can analyze!


(Phil) #4

Makes sense. It also correlates with the graphic example of bacteria growing across the gradation of increasing antibiotic concentration. When put into stress, a few individuals are better adapted, and their genes later bloom like the bacteria and become the dominant population, only the petri dish is the whole environment.


#5

First, I think “most species originated at the same time” is a bit misleading on the part of Tech Times. At least from my reading, the authors found that mitDNA lineages coalesced to about the same time period for the modern populations they looked at and with the data they had at hand.

Population genetics isn’t my strong suit, but the first question that pops into my head is to ask if this is what we would expect to see with your run-of-the-mill populations. IOW, would you expect a continuous population to have mitDNA lineages that coalesce to 100,000 years before present as a consequence of standard population dynamics? If our resident pop gen experts could chime in I would be really interested in what they have to say.


(George Brooks) #6

@T_aquaticus

Do you mean this?:

Let’s suppose you are the Prometheus aliens, salting a planet with 10 different kinds of life forms.

And you set up the robotic sensors to detect when a speciation occurs.

In approximately how many years would we expect the first speciation to occur, the last speciation to occur and the average speciation?

As my earlier post indicated, all of this depends on changes in the ecological niches where these life forms are.

If it was Earth during the Jurassic Age, for example, it might take millions of years before speciation to occur… and not everywhere.

Earth during the last 800,000 years had 8 massive ice ages, which reached out and “bear-hugged” huge swaths of the planet. In the northern hemisphere, there wouldn’t be a population not affected! - - high or low, fast or slow, vegan or meat-eating.

The 100,000 to 200,000 time range is actually pretty impressive. Because it means, say, 30% of the resulting species (in the here and now) were speciated 2 ice-ages ago, and, say, 50% of the resulting species in the here and now were speciated 1 ice age ago. This leaves a small group that comes from before 2 ice ages ago. Even if you want to fiddle with the percentages, I think you get the jist !


(Ryan weatherly) #7

We are not separate from the world around us , what effects us , effects everything around us …
Pressure on us , is also pressure on birds , snakes , deer , squirrels , amphibians , insects , etc etc etc —>

It stands to reason if pressure from stimuli effected us , it effected other species too


(George Brooks) #8

@1god

Agreed. Keeping in mind how big is the influencing factors, and how likely it is to embrace everyone.
In the Cambrian, the factor was oxygen. That’s pretty much going to touch everyone.

The interesting thing about the article was the oddly specific time range 100k to 200k. I kept staring at those numbers, wondering why they seemed so familiar. And then I realized that I had just written a long post elsewhere about 8 ice ages in 800,000 years… and that the times would elegantly reflect those new species populations that emerged from the most recent ice age … AND reflect another group of new species populations that emerged from the ice age before that!!


#9

That’s not what I am picturing.

What I am picturing is a continuous population that hasn’t speciated and has had a relatively constant population over the last 1 million years. If we look at their mitDNA today we see that it coalesces to a most recent common ancestor who lived about 100,000 years ago. If we were able to get some ancient DNA from ancestral fossils of that same continuous population we would find that their ancient mitDNA coalesces to a most recent common ancestor who existed 100,000 years before them. It just so happens that the emergence and extinction of mitDNA lineages over time tends to create MRCA’s that existed about 100,000 years prior to the living population. That’s what I am picturing (which could be completely wrong).


(George Brooks) #10

@T_aquaticus,

Since I’m not very familiar with the current genetic lab jargon, let me ask a question that will clarify what you mean in my mind:

This coalescent factor, would you use the same terminology if you were estimating when two marsupial populations in Australia shared a common ancestor?

The carnivorous Tasmanian Devil and a vegetarian mole, very different kinds of marsupials, present genetic configurations that indicate they both descend from a common marsupial population (a more generalized species) that migrated from the future South America, through the iceless future Antarctica, to Australia, while the continents were still hugging each other in a Pangea-huddle.

Would you use the same terminology and methods to estimate when they diverged from the shared lineage?

In this experiment, the conditions of a diaspora into an empty continent offer the reverse conditions of a common population that finds itself subjected to the environmental stress of an oncoming Ice Age! In the Australia example, competition for resources creates a bonus for any outlier sub-groups that can specialize its exploitation of a eco-niche; every facet of Australia’s environment becomes a potential bonanza for any animal that happens to have a genetic predisposition to live well in that environment.

In the Ice Age example, the cold and ice is coming, and the groups that can best cope with the temperatures and changing food supplies don’t travel as far for survival as the groups that are least capable of living that way, which creates the geographic separation necessary for speciation.


#11

Essentially, yes.

With mitochondrial DNA it is a bit different. Over time there are mitDNA lineages that go extinct and others that flourish.

Over time you will have one lineage that dominates, but it doesn’t mean that there was a bottleneck in the population at that time. It simply means that some females didn’t have female offspring of their own and that distant cousins will inevitably have offspring together (i.e. pedigree collapse).


(George Brooks) #12

@T_aquaticus

I am attempting to apply your terminology to the problem at hand… estimating when two populations diverged.

So I can’t tell how relevant your mitochondria observations are, but I’m pretty sure your bottleneck comment is for a different situation.


#13

I will again start with the caveat that population genetics is not my strongest topic, so others should feel free to correct me.

There are many generations between the descendant population and the ancestral mtDNA most recent common ancestor (MRCA). Mutations occur in between the ancestor and descendants, and if you know a bit about the population size, generation times, and mutation rate you can come up with an estimate for the time between ancestor and descendants. This is known as the time to coalescence since the different mtDNA lineages branching off from the MRCA meet up, or coalesce, in that time period.

What I am saying is that you can have a single shared ancestor for mtDNA without a bottleneck. Therefore, it may not make sense to say that a species “started out” 100,000 years ago simply because the coalescence calculations put the MRCA at 100,000 years before present.


(George Brooks) #14

@T_aquaticus

Ahhh… I thought there was something “odd” happening with one of your sentences.

So… since mtDNA can survive unchanged as it passes along from one population to subsequent “new” or “speciated” populations (that’s interesting, isn’t it!)… then for the purpose of calculating speciation timelines, mtDNA should be ignored - - with one exception: if the mitochondrial DNA shows a persistent change… then we have to be ready to find any other indicators that tell us whether: a single species has broken into 2 different mitochondrial groups … or that the shift in mitochondrial DNA is actually part of the evidence for a “new” population (aka: a population that is a new species).


#15

mtDNA does change over time which is how they are able to calculate time to coalescence. However, just because many mtDNA lineages coalesce to a single ancestor does not mean that this single ancestor is representative of the founding of a species. This is where this diagram comes into play:

There are the same number of individuals in each generation, and it is a continuous population. There is no reason to think that the species started with the black individual at the top of the diagram just because that lineage became dominant in later generations. There are also tons of different genes throughout that population’s genomes that coalesce to a different person in different generations, so it is also a bit arbitrary to use mtDNA as the sole indicator of when a species started in the past.


(George Brooks) #16

@T_aquaticus

A similar analysis has been done with surnames… especially in China. If we, for the purpose of this discussion, conclude that there are more families named Lee in China than any other surname, some might conclude that an early Lee male was particularly “fruitful”, and had more and more offspring with fruitful Lee males.

But math shows that when you have a system where there is gender-dominance (female-only survival of mitochondria, or male-only survival of surnames), even when all other factors are equal, it is a ‘random walk’ regarding the winnowing out of perfectly good mitochondria or surnames. Eventually any diverse mixing becomes increasingly less diverse in a “winner take all” dynamic!


#17

Precisely. You don’t need to have the “start of a species” in order to get these MRCAs. They will naturally occur in any continuously reproducing population. What a bottleneck would produce (if my understanding of pop gen is correct) is a lot of alleles with the same time to coalescence. After skimming the paper in the opening post I don’t think they looked at a lot of different genes across the entire human genome and instead focused on mtDNA, but I could be wrong.


(Phil) #18

This topic was automatically closed 6 days after the last reply. New replies are no longer allowed.


(Matthew Pevarnik) #19

(George Brooks) #20

Too much of so much ?

Here is the live link to the article:

LIVE LINK TO CE-DEBATE ARTICLE

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