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From: John Harshman <john.harshman@gmail.com>
Newsgroups: talk.origins
Subject: Re: Science has a news article up about "living fossils"
Date: Wed, 13 Mar 2024 06:28:17 -0700
Organization: University of Ediacara
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On 3/12/24 10:59 PM, jillery wrote:
> On Tue, 12 Mar 2024 09:04:22 -0700, erik simpson
> <eastside.erik@gmail.com> wrote:
> 
>> On 3/12/24 6:44 AM, John Harshman wrote:
>>> On 3/12/24 3:50 AM, Ernest Major wrote:
>>>> On 11/03/2024 23:28, John Harshman wrote:
>>>>> On 3/11/24 4:17 PM, RonO wrote:
>>>>>> https://www.science.org/content/article/these-gars-are-ultimate-living-fossils
>>>>>>
>>>>>> Open access article:
>>>>>> https://academic.oup.com/evolut/advance-article/doi/10.1093/evolut/qpae028/7615529?login=false
>>>>>>
>>>>>> These researchers looked at Gar, but it also applies to sturgeons.
>>>>>> These two bony fish lineages seem to have a very slow rate of
>>>>>> molecular evolution.  The changes in their DNA accumulate so slowly
>>>>>> that two lineages separated for over 100 million years can still
>>>>>> form fertile hybrids.  3 million years is pushing it for species
>>>>>> like lions and tigers that can still form hybrids, but the hybrids
>>>>>> are sterile. Bonobos and chimps are around 3 million years divergent
>>>>>> and can still form fertile hybrids, but the claim is that these fish
>>>>>> evolve orders of magnitude more slowly than mammals.
>>>>>>
>>>>>> The Science news article claims that mammals accumulate 0.02
>>>>>> mutations per site per million years, while these fish averaged only
>>>>>> 0.00009 mutations per million years.  For the 1100 coding exons that
>>>>>> they looked at for this study these fish evolve much more slowly
>>>>>> than mammals.
>>>>>>
>>>>>> The news article notes that other "living fossils" such as
>>>>>> coelacanths (0.0005) evolve faster, but slower than amphibians
>>>>>> (0.007).  It sounds like terrestrial animals evolve faster than fish.
>>>>>
>>>>> If it's repair mechanisms they hypothesize as the cause of slow
>>>>> evolution, they really should be looking at junk sequences rather
>>>>> than just 4-fold degenerate sites. I suggest introns. And if the
>>>>> introns aren't alignable, well, that kills the theory right there.
>>>>>
>>>>
>>>> Tree species thought to be separated by tens of millions of years are
>>>> known to hybridise. For example Platanus orientalis and Platanus
>>>> occidentalis, and also with Tilia, Quercus and Aesculus. In the case
>>>> of Tilia I suspect that multiple rounds of introgression has served to
>>>> limit the amount of divergence between species. However Tilia does
>>>> appear as a short branch in cladograms, supporting the hypothesis that
>>>> forest trees have a lower rate of evolution.
>>>>
>>> Then again, ducks that are thought to be separated by tens of millions
>>> of years are also known to hybridize, and their rate of evolution isn't
>>> particularly slow.
>>>
>> All sorts of seemingly long-separated species (both plant and animal)
>> are observed.  What determines whether the hybrid offspring are fertile,
>> infertile or sterile?  I found an article on Big Think
>> https://bigthink.com/the-past/soviet-human-ape-super-warriors-humanzee-ivanov/
>> describing an unsuccessful attempt to produce a "humanzee".  Fortunately
>> it didn't work.  The chromosome count is different in humans and
>> chimpanzee, but does this imply that it's essentially impossible?
> 
> 
> My understanding is, the limiting factor is the compatibility of mtDNA
> with nuclear DNA.  As species evolve, mtDNA mutates faster than
> nuclear DNA, but they still need to maintain compatibility with each
> other.  Organisms where the two are poorly compatible fail to thive or
> even to survive.  Over time, isolated populations can evolve mtDNA
> that are no longer compatible with nuclear DNA from other populations.
> ISTM infertility between isolated populations would be a natural
> though not necessarily inevitable consequence of having two separate
> DNA pools.
> 
> *********************************
> Zhang C, Montooth KL, Calvi BR. Incompatibility between mitochondrial
> and nuclear genomes during oogenesis results in ovarian failure and
> embryonic lethality. Development. 2017 Jul 1;144(13):2490-2503. doi:
> 10.1242/dev.151951. Epub 2017 Jun 2. PMID: 28576772; PMCID:
> PMC5536873.
> **********************************

That's one of several possible reasons for incompatibility. Some others 
have already been mentioned.