[ExI] evolution problems

John Clark johnkclark at gmail.com
Sat Sep 15 22:12:30 UTC 2018

On Fri, Sep 14, 2018 at 4:14 PM Darin Sunley <dsunley at gmail.com> wrote:

> One thing that's always puzzled me about the standard abiogenesis
> narrative: how do unicellular creatures evolve into multi-cellular
> creatures with tissue differentiation, that also use gamete cells for
> reproduction that contain the DNA of all of the tissue types?

A single celled animal doesn't just keep getting bigger, when it gets to a
certain size it divides in half, and then the 2 halves don't instantly
divide again, they wait for it to get bigger.  So even single cells must
have some mechanism that tells it when it should and should not divide. I
can imagine a mutation where the cell divides but the 2 halves don't
separate but remain stuck together. However after a few doublings you'd
have a roughly solid sphere of undifferentiated cells and after it got
larger than a fraction of an inch or so diffusion would no longer be good
enough for the cells in the interior to receive nutrients and so the
creature would die. Thus another mutation would be necessary that keeps
track of how many doublings have occured since it was a single cell
(restricting the animals size) or have the ability to detect the presence
of other cells around it and making the decision to divide or not based on
that (restricting its shape). After that yet another mutation tells the
cell that after N divisions, or N other cells in the immediate vicinity
surrounding it, to develop differently. Now that all the cells are not
identical and the creature has a definite shape and Evolution can treat the
entire thing as a segment and say "repeat this entire segment N" times. Now
you're starting to get structure and a body plan.

You've probably noticed I haven't mentioned sex at all and that's because
it's far more difficult to explain why  Evolution came up with sex at all.
Yes sex is good for the long term well being of the species but Evolution
doesn't know that because Evolution has no foresight so every change must
offer a immediate advantage or Evolution would not favor it. It takes a
great deal of effort to find a mate and even then only half your genes get
passed to the next generation, it would be so much less trouble to
reproduce asexually. and then all your genes enter the next generation, and
yet every multicellular creature engages in some sort of sexual
reproduction, with one baffling exception.

The Bdelloid Rotifers are a class of small (although big enough to be
visible if you have good eyes) freshwater worms that reproduce asexually
and only asexually and have been doing so for 80 million years. The
Evolutionary mystery isn't why they are doing it but why doesn't everybody.

 John K Clark
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