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From: Ernest Major <{$to$}@meden.demon.co.uk>
Newsgroups: talk.origins
Subject: Re: The egg or the chicken
Date: Fri, 8 Nov 2024 07:44:04 +0000
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On 07/11/2024 20:41, RonO wrote:
> On 11/7/2024 10:43 AM, Bob Casanova wrote:
>> On Thu, 7 Nov 2024 09:39:14 -0600, the following appeared in
>> talk.origins, posted by RonO <rokimoto557@gmail.com>:
>>
>>> https://www.sciencedaily.com/releases/2024/11/241106132114.htm
>>>
>>> This news article claims that nature could create eggs long before it
>>> invented chickens.
>>>
>>> There is a single celled eukaryote (Chromosphaera perkensii) that
>>> branched off from animal cellular life forms a billion years ago before
>>> protists evolved.  It is a single celled organism that can form balls of
>>> two types of cells that look like early stage embryos, and it exists in
>>> these balls for about 1/3 of it's life cycle.
>>>
>>> The article claims that single celled animals could form embryo like
>>> cellular complexes long before multicellular life forms evolved, but the
>>> most their work indicates is that the genes that could be used to evolve
>>> multicellular life and future embryos may have existed that could allow
>>> the evolution of the convergent trait in two divergent lineages
>>> separated by half a billion years of evolution.  It branched off from
>>> the lineage that led to multicellular life a billion years ago and some
>>> time during it's evolution since splitting off it evolved the means to
>>> form these balls of cells.  A half a billion years after the divergence
>>> the lineage of multicellular animals evolved something similar.  For all
>>> we know the lineage of multicellular animals evolved embryos half a
>>> billion years ago, and the independent lineage of C. perkensii evolved
>>> their ability more recently, unless they have evidence that these embryo
>>> like structures existed a billion years ago.
>>>
>> You don't have to go that far back; even if we have no
>> fossilized eggs of fish or amphibians (due to the lack of
>> hard shells) we do have fossilized reptile and dino eggs,
>> which preceded chickens (or any other avians) by quite a few
>> million years. So I'd rate the article as "interesting, but
>> nothing really new regarding the old question".
>>>
> 
> They are claiming that they have what preceded eggs.  This is before 
> sperm and egg produced embryos.
> 
> Ron Okimoto
> 

A preprint of the paper is available on BioXRiv. What the paper actually 
claims is that the Chromosphaera division phase parallels early 
embryonic development.

They report a life cycle of ~65 hours of a growth phase of single cells, 
followed by a division phase of ~30 hours during which the cell divides 
repeatedly, resulting in hundreds of cells, without a further increase 
in volume. On termination of the division phase the cells are released 
presumably to start the next growth phase. They report that the released 
cells are of 2 or 3 types - mitotic (aflagellate, capable of division) 
and flagellate/amoeboflagellate. They don't go on to investigate the 
roles of the different cell types in the life cycle.

Different forms of borderline multicellularity occur in several other 
holozoan groups. I'd doubt that the state in Chromosphaera represents 
the ancestral state, though they do make a case for the involvement of 
the same genes in animals and Chromosphaera. (It's been known for some 
time that the basis of the tool kit for animal multicellularity is 
present in other holozoans.)

They don't make much of this, but the Chromosphaera life cycle could 
still be ancient, which casts doubt on the animal interpretation of the 
Doushanto "embryos".

-- 
alias Ernest Major