[ExI] evolution problems

[Dan TheBookMan]

On Sep 14, 2018, at 1:11 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?

I wouldn’t call that abiogenesis — which isn’t about how multicellular organisms evolve, but how life itself gets started. By the time you get to multicellular life, it seems the origination is (in the standard view) already more than a billion years old. But, yeah, the origins and development of multicellular life is puzzling and an active area of research — no matter what the correct label is.

> It's easy to see how you can go from unicellular creatures to colony creatures with tissue differentiation. And it's easy to see how you go from unicellular creatures reproducing via fission to unicellular creatures reproducing sexually.
> 
> The problem seem to be that, once you're a multi-cellular colony creature with differentiated tissues, it's very hard to see how you get the DNA from all the subspecies back into a single subspecies of gamete cell. Conversely, it's also difficult to see how, if you're a unicellular species that reproduces sexually, how to you accumulate and absorb other species for tissue differentiation?
> 
> Summing up, it's easy to see how one feature (tissue differentiation) or the other (gametes) evolves, but I've never heard an even remotely convincing narrative about how you end up with both features in one species.

I believe the evolution of differentiated tissues and of germ line cells long predated the Cambrian Explosion. I believe the latter is more the evolution of easily preserved multicellular organisms... probably because of the evolution of protective layers and maybe if vision.

However, this doesn’t answer how differentiated tissues themselves evolved.

> Speculation: however it ended up happening, I strongly suspect it's the single innovation that caused the Cambrain explosion. And given how late the Cambrian explosion was in our planet's prehistory, it may have been a seriously difficult hump for evolution to get over. And may therefore be a prime candidate for the Great Filter.

It might be, though the presumption then is life has to basically follow the same progression and timeline elsewhere as here. Given we don’t yet have any data on how life evolves elsewhere and our data on how it evolved here is fairly sketchy, it’s highly speculative.

Regards,

Dan
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