why DID we evolve into humans?

quote:

---

But, I wasn’t really concerned specifically the eye, or how or why it evolved, but the order it evolved. Our bodies are so complex, when did all that complexity get there?

​

According to evolution, was it before our last common ancestor (common to all mammals, and maybe even fish and insects), or did all the mammals etc develop all this complexity independently from each other?

​

In other words: was there some creature that had eyes, ears, liver, heart, spleen, (all that good stuff), and through mutations, some gradually became giraffes, others become people, or cats, bears, etc?

​

I understand no one claims we went from (for example) bacteria to human in one step, that every change was very gradual, so please don’t get sidetracked on my language above.

---

Well, to pick just one example of yours, I think complex eyes first appear in some ancient fish. Its descendants (which includes modern fish, amphibians, dinosaurs, and of course people) inherit the complex eyes and theirs evolved further to suit their particular needs. It's a valuable inheritance, so creatures didn't lose it.

I’m not an expert in autonomy, but I know that many creatures share some of the same organs that we do. Many different creatures have ears, eyes, liver, and kidneys. I’m sure that there are many more.So you are saying these organs evolved in our common ancestor (maybe a fish, in your example), meaning we had a biologically complete common ancestor. I don’t know of any organs we have that no other creature has, so a complete ancestor means biologically, they had all the organs we do now, they just weren’t human.At that point, we had a non-human ancestor with everything it needed to change into a human. So it then grew legs (over small steps, not in one big jump), arms, etc, learned to stand upright, and then became smart (to become human)Others could have evolved into dogs, lions, etc. through the same small step evolution process.So does that sum this up?

You got it correct. Of course the whole process took about 400 million years and the fish common ancestor did not just produce humans, but others.

We are what we are because we made more use of what we needed daily and the more we used parts of our bodies the more they evolved. Giraffes needed to stretch their neck to reach higher and higher branches and over millions of years their necks and legs evolved because they used those parts of their bodies more. We have eyes because our bodies were bombarded with light waves so we developed organs to sense light. We were bombarded with sound waves so we developed organs to sense sound. A common ancestral path of evolution may have provided the building blocks but usage and in turn greater usage made our eyes or other body parts what they are. Animals that relied on their eyes to hunt or avoid being hunted mostly have better eyesight than herbivores or animals with minimal threats.Likewise, we used our hands more and more and they developed to be more useful to us. We used our brain more and more so it evolved more that other primates. We used our voice box so it evolved and carried with it the ability to enunciate a wider arrange of sounds. We stopped hanging from trees upside down so our tails disappeared and our toes evolved to meet our desire to walk upright. And this happens over millions upon millions of years. Evolution is a game of use it or lose it.We could only guess what path evolution could take us on if we happen to by some slim chance provide for a habitable environment on this planet for another million years. Our brains could evolve much further so we use more of it than we do now and unlock its true potential and it might be much more common place for the masses to comprehend complex ideas?

That is not a correct statement of how it happens.This message has been edited by NosyNed, 08-10-2004 04:07 AM

What would a correct statement of how it happens be?I believe the constant stretching to reach food higher on the tree tops over the course of generations upon generations would in fact give rise to stronger neck muscles, stronger leg muscles, longer necks, and longer legs. Its no different then the brontosaurus and the T-rex. T-rex evolved to have lots of sharp teeth and brontosaurus to have long necks because over hundreds of thousands possibly millions of years the physical form evolved to suit the environment.This message has been edited by nipok, 08-10-2004 04:22 AM

I belive that the mistake you are making is assuming direction and purpose.What seems to be happening is something subtly different. Our hands did not evolve because we used them more. Rather, by chance, some humans were born with a slightly different hand that allowed them to do things that others could not. Them that could had an advantage over them that could not and so had a greater chance of living to reproduce.In the case of the giraffe, one was born that could reach a food source that others could not reach. Again, just random chance. Having a food supply that the others could not reach was an advantage, so the longer necked critters had a better chance to live long enough to reproduce.JMHO & YMMV.

---

Aslan is not a Tame Lion

No, because those changes aren't carried to the offspring.If you cut the tails off of rats, it doesn't matter how many rats you do it to, for how long - none of their offspring are born without tails.The environment causes selective pressure, but the environment doesn't itself create new morphologies to select. (That's a function of random changes at the genetic level, called "mutations", though we wouldn't know that till much later.) This thinking was Darwin's great breakthrough; it replaced the thinking you exampled above, called "Lamarkianism", named for its most famous proponent.

It can't though, as those changes are not passed on to offspring.If I lose my arm in a war, my children are still born with arms.

quote:

---

If you cut the tails off of rats, it doesn't matter how many rats you do it to, for how long - none of their offspring are born without tails.

---

Do we know that for sure? Lets do it for a thousand years and then see.

We certainly know that for grass. You would think after getting cut weekly for several decades it would learn to keep its head down.

---

Aslan is not a Tame Lion

Fair point.Although, wheat is a grass that has been substantially modified by its coexistance with humanity. Now, I'm not suggesting that Lamarckism is right, I guess the case can be made that the human intervention merely creates a probabalistic space into which evolution can design, as it were.This message has been edited by contracycle, 08-12-2004 08:39 AM

The only hitch would be getting the grant application approved. But once you had it through, you're off the hook for a millenium!!

Assuming that you do it surgically, and there's little to no risk of death for the rat, then yes, I think we can conclude that we will not, as a result, have a population of rats without tails.If we used rusty scissors and most of the rats died during the procedure, we'd go through a lot of rats, but we might have a population of tailless rats, because we would have a selection pressure against rats with tails.I realize that you probably knew that, but this was for the benefit of the audience.

Assuming that the death rate was due only to the act of cutting off the tail, and the initial length of the tail had no effect on the morbidity, then we would have to wait, I suppose, for a mutation that would produce no tail at all, all at once.