Friday, March 27, 2009

Evolution, Generations, and Deep Time

"My grandfather wasn't no monkey!", "You think we came from slime?!", and "man, if you want to believe your great^100 grandpa was a rock, be my guest...but it's STUPID!". The latter was actually left on a use.net forum awhile back. They're all too familiar to those of us who defend evolutionary biology from the constant onslaught of religious opportunists who prey on their theistic victims for personal or political gain.

Talk Origins contributor Aron-Ra and I take a stab at responding to these objections based on Aron's Post of the Month, July 2002.

In a "powers of ten" style look at deep time, "Dark Syde" looks at what science believes the ancestors of humans were.

I figure at 20 years per generation, 100 generations of grandfathers would equate to twenty centuries. That means the grandpa you're talking about was a contemporary of rabba Yeshua bar Yosseff just 2,000 years ago.
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Increasing the multiple, your great^1,000 grandpa would have had even shorter generation gaps, being about 14 or 15 years apart on average. He would have been a Paleolithic nomad in about 13,000 BCE, just shortly before the foundation of the most ancient cities like Jericho and Damascus. He still would have been fully human and already a member of the only surviving human species, Homo sapiens.
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Your great^10,000 grandpa and grandma would have been everyone else's great to the Nth grandparents too. (Everyone alive today that is) He would still have been definitely human and visibly different from his Neanderthal neighbors. Whether he would be considered Homo sapiens yet 140,000 years ago or still classified as H. antessesor or heidelbergensis doesn't really matter. All are still obviously people and no more ape-like than any of the more isolated aboriginal primitives still around today.
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Your great^100,000 grandpa might now be called Homo ergaster or erectus having lived some 1.3 million years ago
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And his great^10,000 grandfather would have been called Homo habilis or rudolfensis. Any or all of them would have appeared to be a bit more ape-like than the most monkey-faced modern guy, but he still would have been definitely human, especially when compared to the other fully bi-pedal apes that were wandering around a million and-a-half to a couple million years ago.
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Your great^1 million grandpa on the other hand is quite a leap away from Homo erectus....There were no definite humans yet, but there were other hominids even though none of them could walk on two legs for very long.
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At six or seven years between generations, your great^10 million grandpa would have been barely recognizable as a primate, looking almost as much like a squirrel.
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Your great^100 million grandpa was a shrew-like mammal darting through the Jurassic underbrush 170 million years ago.
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Your great^1 billion grandpa would have lived under water along with everything else, including trilobites and some really alien beasties a few hundred million years ago and at least a couple hundred million years before the first dinosaur.
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The world of your great^10 billion grandfather wasn't much different from that which was already described, although there were a lot fewer trilobites then. And he wasn't a swimming worm yet. He would have been a roundworm, if he would have been considered a worm at all. He may have looked more like a jellyfish with a sense of direction.
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Your great^100 billion grandfather may not have been an animal yet, but a sort of co-op of bacteria living inside a single membrane: The mitochondrion, Golgi apparatus, nucleus, and other bacterial endosymbionts, all of which have their own individual ancestry.
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Your great^1 trillion grandfather would have been various bacteria before they learned to cooperate in a single eukaryotic cell.
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And your great^10 trillion grandfather would have been bacterial too.
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Your great^100 trillion grandfather may have been an even simpler chemosynthetic protien in an inhospitable world unrecognizable as Earth.
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Even earlier, with 'generations' now coming every few minutes and represented by chemical hypercycles, your 'ancestors', for lack of a better word, would have been macromolecular cycles in which the end result of a given chemical reaction is the constituents to fuel the next leg, which ultimately circles back around to any one reaction. This is the earliest we can go back in terms of proto-biology (Abiogenesis) and it's chock full of speculation at that. We are now at just over 4 Billion years ago.

Before that, we have the formation of the Earth, of the solar system, of the galaxy, and the universe. Of course, before about four billion years ago, the whole notion of "generations" has long since ceased to have any meaning.

But it's quite a tale.

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