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From: jillery <69jpil69@gmail.com>
Newsgroups: talk.origins
Subject: Re: Science has a news article up about "living fossils"
Date: Fri, 15 Mar 2024 03:45:24 -0400
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On Wed, 13 Mar 2024 06:28:17 -0700, John Harshman
<john.harshman@gmail.com> wrote:

>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:
>>=20
>>> 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-fo=
ssils
>>>>>>>
>>>>>>> Open access article:
>>>>>>> =
https://academic.oup.com/evolut/advance-article/doi/10.1093/evolut/qpae02=
8/7615529?login=3Dfalse
>>>>>>>
>>>>>>> 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.=C2=A0 The changes in their DNA accumulate so=
 slowly
>>>>>>> that two lineages separated for over 100 million years can still
>>>>>>> form fertile hybrids.=C2=A0 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.=C2=A0 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).=C2=A0 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-iv=
anov/
>>> 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?
>>=20
>>=20
>> 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.
>>=20
>> *********************************
>> 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=20
>have already been mentioned.


My understanding is there are likely several causes for genetic
incompatibilities.  My impression is chromosome count is among the
least of them.  As long as the important genes line up during meiosis,
it doesn't really matter if the chromosomes are in multiple pieces.
That's why for example the chromosome 2 fusion wasn't as big a problem
for our ancestors as some claim.

OTOH mtDNA/nuclear DNA incompatibility is an insurmountable problem.
Since the original endosymbiosis billions of years ago, mitochondria
have transferred much of their DNA into the nucleus, in order to speed
their duplication, while keeping for themselves most crucial genes,
for example to regulate ATP synthesis. =20

Having two separate pools of DNA with different mutation rates
necessarily means that from time to time some gamete fusions will
combine two incompatible pools.  Breeding long-isolated populations
makes that even more likely.  And once two populations are
biologically isolated, for any reason, they necessarily evolve
independently of each other.

--
To know less than we don't know is the nature of most knowledge