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His question is what I was answering. Have we weakened ourselves as a species by interfering and keeping alive, through various means, those with physical or other disabilities/vulnerabilities? He provided the Japanese crabs as an example, the implication is that what if these crabs were not the ones who would have survived on their own, so we've doomed that species.

My response is that the process works differently for humans, where physical strength, and being able to resist various ailments/viruses, etc. is not key to the survival of the species, brains and skills on the other hand are.

I don't care if Hercules re-appears, he will not be able to stop a meteor, human brains on the other hand may be able to develop a way to stop that particular event, which could really save the entire species.

yes, i'm agreeing with you pacisdream. our unique ability to think, predict, create is the very trait that has allowed us to survive as a species, and it doesn't seem possible to me that we can set those skills aside and allow natural selection to breed us into a physically hardier race, because, as you say, even hercules cannot stop a meteor, so brawn is ultimately less important to our survival than brains. if we abandon "intervention" we will likely die out.

Late to the discussion, too much pondering aliens lately :)

I think it's undeniable that we're weakening the species from a purely physical perspective. For example, I have weak eyesight, most of my extended family has weak eyesight to some degree. In times past we would have been predator food as well as ineffective hunters. Now it doesn't matter.

Evolution is usually expressed as "survival of the fittest" but in reality, survival is only a filtering prerequisite. The real driver is sexual selection and actual frequency of reproduction. While it is tempting to believe that evolution in humans will proceed toward greater intelligence, the casual observation that brainy folks tend to delay reproduction and have few kids while the trailer parks are lousy with youngun's would seem to argue against that.

Finally, it is my understanding that macro-evolution is driven by a process whereby a sub-group becomes isolated from the main population -- through geography for instance -- and due to particular environmental pressures develops characteristics different from the main population. I don't see that occurring in humanity unless we engage in some radical kind of migrations like interstellar colonization.

Dutch

One nitpick here (but one I think is important), natural selection and evolution are two different things.

Your eyesight is bad due to either hereditary or environmental issues (working in office environments, we tend to use our eye muscles less, and those muscles get weaker). The one I think is more pronounced is wisdom teeth.

I am not sure I follow the trailer park example. Yes, economically disadvantaged folks seem to have more kids, but this says nothing about the economically advantaged and more educated/more intelligent ability to survive. In fact, our own American experience should serve as proof that this is not the case. A smaller number of technologically advanced Europeans wiped out most of the human inhabitants of this continent (and some animal species as well). Another example is how the US armed forces, inferior in numbers but superior in technology and know how, easily defeated the Iraqis (not a comment about the war).

Did you mean Macro or Micro evolution? There are a few examples of human Micro evolution in the jungles of Brazil.

Pacis,

Our eyesight issues are hereditary, no doubt.

As to your second paragraph, you seem to be equating the social/cultural with the biological. While we do have various sub-populations within the human species, those differences are VERY minor and don't constitute anything like sub-species. The different racial groups simply weren't isolated enough, or for long enough, for anything like speciation to occur.

So I guess I'm talking about Macro evolution. And I imagine that any significant evolution of our species stopped with the advent of agriculture or shortly thereafter. At least the selection pressures have shifted so that now, if anything, our primary pressures will be socio-economic. It's my understanding that survival is one pressure, whereas sex is another. The survival selection works mainly to cull the herd -- eliminate unhealthy variations -- while the sexual selection is what can induce change within otherwise genetically stable populations.

Of course, I'm not an evolutionary biologist so I could be completely hose in all this... :-P)

Dutch