leroy
Well-Known Member
Thanks for sharing.Hi Leroy. I realize that you are battling Sheldon. I don't have any interest in defending Sheldon, but the old biology major in me did find this thing you wrote interesting.
I think that's very likely true. Even the simplest prokaryotes (bacteria and archaea) are almost fantastically complex when one gets into their detailed molecular biology. So the chances that they popped fully formed out of some "primordial soup" seems to me to be vanishingly small. That suggests that they are descendents of simpler precursers that no longer exist today (why?). If we speculate about what those hypothetical precursers might have been like, we get to things that probably don't deserve the title "living thing", such as naked chemical replicators (nucleic acid strands?) without cell membranes or any sort of protein synthesis or energy metabolism.
In other words, I hypothesize an extended period of chemical evolution that proceeded the advent of biological evolution, in which the structure and machinery of the simplest cells was hammered out.
Yes, I think that's true of what we can tell of the history of life on Earth.
Yes, that's my working assumption. I can't really say that it's something that I actually know, it's more along the line of an explanatory hypothesis. It's the best explanatory hypothesis that I know at this point, certainly the best at not raising more questions than it answers. (Explanations seek to reduce the unknown to the known and not multiply the unknowns.) It seems to be consistent with a huge body of observed evidence, from the fossil record to comparative genomics. But it isn't "proven" in any apodeictic (logically necessary) sense.
It's probably wrong to say that natural selection has a "preference". That's anthropomorphizing things. But I do think that evolutionary processes tend towards greater complexity as time goes on.
If a chemical replicator is able to form many different chemical permutations, and if some of those permutations increase the ability of the replicator to successfully replicate and other permutations reduce that ability, then subsequent iterations/generations will increasingly display the successful permutations. These kind of changes are cumulative, they add on each other. That's how I imagine the first cells appearing.
Then if all the cells are doing is reproducing, new changes that enhance the reproduction will tend to accumulate. We see that with the bacteria and archaea, which have continued evolving down to the present. Their new innovations have generally been metabolic, the appearance of an amazing variety of new metabolic pathways that enable them to exploit new habitats.
That growing complexity needn't happen at a steady rate. We might see evidence that it doesn't in the "Cambrian explosion" (or the preceeding Edicaran period, where the plant and animal lines seem to have diverged and large multicellular organisms make a sudden appearance.) Cells had been living in colonies since the very beginning and colonies provided some advantages. But at some point developmental biology took off (stem cells) and the genetic code began to code sequential functional differences in the cells being reproduced as particular genes are turned on and off in order. So we start seeing organisms composed of organized functional collections of differentiated cells. And once the new innovation of developmental biology was in, we have multicellular life, Life 2.0, and we see a sudden explosion of new complexity: body plans, organs... the earliest ancestors of arthropods, molluscs, annelids, chordates all make a sudden appearance.
It's not really a matter of "proof". All evolutionary theory is is an explanatory hypothesis. Evidence for it consists of how well it makes sense of what is observed in all of the biological sciences, from molecular cell biology to biogeography.
So i guess my point is :
Natural selection aims at survivability and reproduction
Natural selection doest aims at complexity
So why do we see an increase of complexity?
To me the answer is simple, Natural selection is not responsible for the increase of complexity there most be an other mechanism. .... or perhaps ancient life on average is as complex as modern life.
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