A good summary of so called human evolution.

Astrophile writes:

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Can you, or anybody else, either refute this argument, for example by identifying other fossil candidates for human ancestry, or by showing that living things can come into existence without having parents?

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Define what you mean by "living."It isn't that easy to do. Currently, we can create self-replicating, auto-catalysing, homochiral molecules that evolve.Are they "living." Is a virus "alive"?You start your post with this:

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We all know that all life comes from life (and usually from life of the same kind), that every living thing (including ourselves) has parents, grandparents, great-grandparents, great-great-grandparents, and so on in an unbroken lineage that extends indefinitely far back into the geological past, through the Pleistocene, Pliocene, Miocene, Oligocene, etc.

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You are making an invalid, post hoc ergo propter hoc assumption: That because all the life we currently see is the product of a reproductive process of another living thing, that means that life necessarily comes from other living things.Well, unless you are going to say that life has always existed, that necessarily isn't true. Even if you are going to invoke magic to zap-poof life into existence, that requires that at some point in time, there wasn't any life and after that point, there was and thus, life does not need to come from living things.But that said, we can't even make the claim that "life comes from life" because casual examination of life shows that it actually comes from non-life: You eat things, break them down into non-living components, and then engage in chemical reactions that incorporate them into the living thing. Remember, you started life as a single cell. You now have trillions of cells. They didn't magically appear and they aren't accumulations of other living things. They were created because that cell took in non-living material and converted it into other cells.So clearly, there is a chemical pathway by which non-living material can be turned into living material.Unless you're going to say that there's some magic in that old cell wall they found. For when they placed it around the nucleus, it began to dance around.But back to my point: The fact that life as we know it now comes from reproductive processes of other living things doesn't mean that life necessarily requires it. It may simply be that it's much easier to make new life once you have some than if you're starting from scratch.Take the creation of water, for example. Suppose you have two moles of hydrogen gas and one mole of oxygen gas. You mix them at STP. You're not going to get any water out of it because there isn't enough reaction energy to start a reaction.But once you do spark the mixture, you get a huge reaction...much more than the energy of the spark that got it started. That's because the energy released from one set of molecules reacting is sufficient to get another set of molecules reacting which then cascades throughout the mixture. If you had a huge volume of such a mixture such that the reaction could be sustained for a significant time, then you might conclude that in order to create water, you need to have a reaction of water nearby. After all, all the water that we see is the result of a previous water reaction. We never see water coming into existence in an area where there wasn't a water reaction going on.But that's not because it can't be done. It's simply because it's easier to get hydrogen and oxygen to react if they're next to a reaction. At the beginning, it was a different chemical reaction that started it which then found a much easier pathway to continue.We don't know how life got started. We have some intriguing suggestions that evolution is showing us and our knowledge of biochemistry is pointing in, but we don't really know.But just because life today always seems to use a biological process to produce new life doesn't mean that's the only way.

Astrophile responds to me:

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This thread is supposed to be about 'so called human evolution', not about defining life or about the origin of life.

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I agree that it was a bit of topic drift. You're a bit new here so let me introduce myself: I'm one of the local pedants who likes to pick at things, even if I agree with the general statement. I like to think of myself as congenial, but I understand that I can come off as an ass.Nice to meet ya.

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My argument was that we must have had Pleistocene, Pliocene, Miocene, etc. ancestors

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And here's me nit-picking even though I agree with you:If you think god zap-poofed life into existence, then no, there is no justification that we had such ancestors. In fact, there are many creationists who make that very claim. They talk of "ages of the earth" and create scenarios where god created, for lack of a better term, "test" animals and these other fossils aren't related to humans at all.Now, I certainly agree that if one presumes that there is a connectedness to life, then surely our ancestors go all the way back to the first life. But creationists don't have that assumption. There is no interconnectedness and certain organisms simply zap-poofed into existence. They'll claim that these fossils that show strong deviation from a typical human are either some form of ape or are merely a deformed human and don't represent a different species of human at all.

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You appear to be raising the alternative possibility that Homo sapiens originated directly from non-living organic or inorganic matter by some sort of spontaneous generation, without evolutionary ancestors. Do you actually believe that this is possible, or is this merely a jeu d'esprit, or have I simply misunderstood you?

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What? Me state my case in less than crystal clear terms? Why the nerve! But since you brought it up...Genesis does say that god makes Adam out of the dust of the ground....But seriously: No, I am not saying that humans were created de novo out of clays around a hot spring. Human life is "too complex" for that. Instead, humans evolved from previous ancestors that go all the way back to the first life. We don't rightly know how life got started in the first place, but it certainly seems to be the case that it started chemically since life is, after all, just a particular set of chemical reactions.As Dobzhansky said: Nothing in biology makes sense except in the light of evolution.