Evolution Simplified

How do we know this?

Observation. How many robin eggs in a nest? Baby possums in a litter?

Ok, I got that. What about the second fact?

Observation again. We aren't up to our eyeballs in robins or possums or even rats and roaches. There have been LOTS of censuses on many different critters for a century or more now - populations may cycle up and down, but the only long-term trends are down in species we humans are squeezing out, and up in ourselves and maybe housecats and cows.

What about in the past when there was no artificial influence from humans? Or does this fact only refer to present times?

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The larger theory does not attempt to explain this.

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- referring to the origin of life...I find this fascinating. Consider this quote from Menand:

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Darwin wanted to establish... that the species ” including human beings ” were created by, and evolve according to, processes that are entirely natural, chance-generated, and blind.

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To show this you have to show abiogenesis (I can't think of another option anyway). I've always assumed that was part of the ToE.At the very least the ToE has to include the first form of "life." And for the above statement to hold true, it should mesh with what we learn about abiogenesis. If life is that eager to start from bare chemicals then how hard can it be? (Ok, ok... I might be exaggerating a little.)

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it either means that life gets started quite easily, or that someone stepped in. considering that right now we cannot prove (or disprove the second), and that abiogenesis is looking like a real answer, then perhaps life does get started easily.

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Hmm, mayhaps we are not so unique after all.

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It seems to me that is one possiblity. I can think of three off the top of my head:1) Outside intervention at ~3.8 billions years ago. (This wraps a lot of possibilities into one.)
2) Life is "likely" and easily "erupts" given the "right" conditions. (Which raises the question why?)
3) Life is "unlikely," but developed in at least one case. (Which raises the question why?)(Ok, technically I can think of others but, IMO, they are exceedingly remote and I'm not going to list them.)I find #3 unlikely but definitely possible. What if we find that life needs conditions X to evolve. What if we find that, given much more knowledge than we have now, that the chance life to begin given those conditions during the life time of a sun is 1/Y. What if we find the # of planets in the universe that meets the conditions specified by X are Z and (1/Y)*Z is not so incredibly small? Not the most interesting possibility but I could buy it.

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There is a thrid possiblity. The way we knew it could 'support' life was that life happened. It could be that it could have supported life earlier, but none happened at that time.

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I grew up on science fiction novels so the idea that very different life forms could exist (like ones that could live in the clouds of jupiter or on the surface of a neutron star, etc.) is not foriegn to me. But it's one of those conjectures that has absolutely no evidence. And we all know that proving a negative is difficult. I'm going to make some assumptions about "life" until I have evidence to the contrary. First, that it's carbon based and, second, that it needs liquid water and oxygen. Yeah, yeah... I've become fairly skeptical in my old age. Provide evidence to the contrary or deal with it. (And I reserve the right to edit that list.)Also, it's not the first time such an argument has been used. Regardless of how unlikely something is (like someone with exactly my DNA make-up coming into existence) if the chances are not zero and it happens, maybe you shouldn't place too much significance on the occurance. But then there's the mathematician in me... if the chances of something happening is exceedingly remote then it's a good bet it won't. And if it did happen, there's probably other factors that increased it's probability that you don't understand (or your model is wrong in other ways).This is why if (1/Y)*Z ended up being < 10^-50 (to use a ridiculously low number) I just wouldn't buy it.

In "The Origin of Species" Darwin is talking about exactly that the origin of new species from old. If you read it you find that the origin of life is passed over in a single sentence and is not an issue for the theory.If you note the fundamentals of the theory it is apparent that it can not be talking about the origin of life. It involves the behaviour of imperfect replicators. It ONLY applies to imperfect replicators. "Imperfect replicator" is as good a rough definition of life as any other given how hard it is to define.The first "life" could have arisen in any way you most like: hand of god; alien invasion; time traveler's muddy boots; chemical inevitability; probabilistic inevitability (low chance but billions of worlds to try it on) and so on. None of that makes the tiniest difference to the nature of the theory of how life evolves after that.

You never played "rabbits and foxes"? It's pretty trivial to model the fact that organisms that need resources from the environment to survive reach an equilibrium with that environment, where their population size is balanced against the amount of the resource the environment can produce. We call the population size that the environment can support "K".

Thank you for that restatement. I believe I got it the first time. The quote from Menand is still interesting and why I assumed otherwise. Yes, yes, I know better now.

The way it's stated, it sounds like he's talking about the present.So your point is that all populations increase up to a certain point and then stabilize?

Well, I think he is, because he's trying to phrase these as observations. We observe that most populations have reached a plateau, and we have every reason to believe that those populations that haven't yet will. Yeah, pretty much.

Seems more like a deduction than an observation. I'm sure there's a whole lot of species we don't observe.

true. the thousands of beetles that have yet to be discovered. The untold thousands of new species of microscopic bacteria.It's all population growth curve. My ecology background is quite limited, but from what I understand, every population has an intial, slow increase in numbers, followed by exponential growth, at which point it exceeds the limit of the habitat and the numbers level off and there is a state of equilibrium.This equilibrium point is determined by the number of organisms in the population that the habitat can support. We do not know, as far as I've heard, when humans will quit our exponential growth curve and begin to level off. And if we make it into the stars, who knows if we'll ever level off.

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Seems more like a deduction than an observation. I'm sure there's a whole lot of species we don't observe.

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It says most species, not all. And I would think that it refers to historic observations as much as the present day in the strictest sense.
Given that, wouldn't the fact of population growth itself tend to make a species noticable ??

I was just trying to figure out if this is a deductive matter, that this state of affairs must be--except in cases in which there is artificial interference by humans.