Has human evolution stopped?

First, I’m amazed at how many people seem to subscribe to the bizarre delusion that “the environment” and “human society” are somehow innately distinct. That’s as stupid as saying that “the natural world” and “human society” are innately distinct.

Evolution has not stopped because it cannot be stopped. Evolution is NOT the same thing as natural selection. Go back to biology 101 if you don’t know the difference. Evolution is merely the name of a change in the frequency of alleles in a population over time. Natural selection is but ONE mechanism of evolutionary direction. Even in a “pure” random walk system, it is possible to have evolutionary direction, by the same method whereby an N-dimension random walk may end up having a post hoc direction in relationship to the starting point at any given moment.

Now that that is out of the way, we move to the next part of the matter: Has our EEEEEEEEEEEEEEEEVIL CODDLING of those vile weaklings made or shall it make us into a race of untermenschen? This question begs the following questions that must first be answered:

What specific settings would these people be “inferior” in?
Is a trait that some people might consider to be “inferior” necessarily and absolutely “inferior” in all cases? (Is it an inferior trait to have sickle cell in your population?)
Do all responses require some daft and daffy Mad Max scenario be activated?
Like it or not, society and coddling the “weaklings” is specifically the evolutionary response our species has to the stresses of life. Indeed, it may very well be the one thing that makes us human. Argue against it and you argue against our species as a whole.

Evolution is still occuring. Consider Wilt Chamberlain, who is said to have slept with over ten thousand women in his lifetime. Undoubtedly, he left behind at least a few hundred children. This means that, in terms of evolution, he was very successful. And the factors which led to him being so successful are at least partly genetic. So the generation after Wilt has a few hundred more individuals prone to being good basketball players. Whatever genes are responsible for being good at basketball are therefore slightly more prevalent now than they were before The Stilt came along.

We can’t tell. It could select for people with an inherited immunity to synthetic progesterone for example. Since this would limit the efficacy of many forms of birth control it would provide a large reproductive advantage.

As others have pointed out, exactly the opposite is true.

Can you provide some evidence that inbreeding has any effect whatsoever on the rate at which mutations occur?

The question is flawed in itself. A trait needn’t be genetically based in humans, it simply needs to be genetically linked. There is a large interplay between memetic and genetic evolution, with one reinforcing the other. Mormonism for example isn’t genetically based, yet it tends to run in families and so is genetically linked. And Mormonism provides an evolutionary advantage in terms of fecundity.

It’s impossible to say conclusively if there are any directly genetically linked factors, since simply knowing they exist can cancel them out. But they doubtless exist. All one needs do is look at what factors are correlated with increased fecundity and see if there is any genetic component. If there is then you have a winner.

To use one controversial example: intelligence. This is partly genetic. Exactly how much so we don’t know, but it doesn’t need to be much. There is a strong correlation between intelligence surrogates such as IQ and education and fecundity. So intelligence (or lack thereof) is a genetic based variation that provides and advantage.

There are numerous other factors that impact on fecundity in western societies, all driving evolution one way or the other. The only way evolution could even slow is all people had exactly the same number of offspring. Far from this occurring we id a greater disparity in reproductive success now than ever before.

Cultural memes also influence human evolution. Any cultures that embrace celibacy for all (Shakers) or self-sacrifice by suicide bombing (Palestinians) will tend to weed themselves out of the gene pool or at least whatever gene makes for a “tendency towards self-sacrifice.”

Not at all. If suicide bombing were a successul way of getting your tribe (ie, those people most similar to you genetically) to be in a dominant position over another tribe, that gene would acually be selected for rather than selected against.

Of course the idea that there would be a “suicide bomber” gene is pretty ridiculous, but a gene that predesoposes some people to self sacrifice for closely related people is not at all ridiculous. There have been many studies of social insects that show exactly how this works (see E.O. Wilson and his work for details).

Did I say a gene for suicide bombing or a gene for self-sacrifice? I’m aware that self-sacrifice can an evolutionary advantage but not necessarily. If that self-sacrifice is expressed by a cultural meme that expresses itself in the form of a behavior not tolerated by others, it might lead to it’s own culling. How about a gene that makes one more susceptible to brainwashing or taking actions that are highly contrary to instinct? With cultural memes like suicide cults and Shakerism that gene might tend to doom itself.

Shakerism, yes, because it has no clear benefit for your relatives.

Suicide cults, if they are directed at preserving your living relatives, might be selected for. It all depends on the purpose of the meme or gene. All that matters is whether or not the gene (or meme) makes it into the next generation at a higher or lower frequency.

The gene doesn’t care if it’s transmitted thru you or thru your brother or sister. In fact, it’s more useful to look at evolution from the standpoint of the gene, not from the organism. As depressing as this may seem, you and I are just vesels that allow genes to replicate themselves. Not the other way around. And the genes (or memes) can get from one generation to the next in any number of ways, not the least of which is to sacrifice you for the sake of the larger family.

Blake, of course you are right. The mutation rate is totally unaffected by who the parents are. Even the prevelance of a deleterious gene is unaffected. Let’s see if I can get this right:

The expression of a phenotype different enough from the norm to be considered a mutation is more likely in a highly inbred poplulation, at least until gentic purging occurs.

Not really. Selection occurs at multiple levels, from gene to species, and the locus of selection may vary from characteristic to characteristic. By and large, examining phenotypes - how the genome is expressed - is more useful than looking at individual genes. Not every gene can be selected in isolation; ultimately, it is the organism which must survive to reproduce, or fail to do so, which determines the fate of not just any specific gene possessed by that organism, but its entire genome. We are, so to speak, more than the sum of our genes.

Some genes are not expressed, or their expression is selectively neutral. It becomes much more difficult to explain the persistance of such genes if one were to examine solely the gene itself (not the least reason of which is that it seems that one must overly rely on anthropomorphization in order to explain anything from the viewpoint of a Dawkinsian “selfish gene”), without respect to its effect on the organism as a whole.

Granted, it may boil down to personal philosophies on the matter, but it has been my experience that the “big picture” of evolution in general, and natural selection in particular, makes more sense from the perspective of organisms than it does individual genes.

The changes in relative frequencies of alleles (one form of “change in heritable traits”) can occur without mutation, but those alleles themselves are a product of mutation. There are also instances of non-genetic changes in traits which are heritable, but those represent a statistical minority, and play little role in the overall evolution of life. Although, instead of “mutation”, a better requirement for evolution in the biological mold would be “variation”.

Natural selection may not be evolution, but it is the primary mechanism by which it operates, and the end results of an evolutionary process absent any variation (and by extension, selection) would be would quite different.

Two words: Punctuated Equilibrium. And I’m sure you’re well acquainted with that effect. There is every reason to believe that we, as a species, are in the Equilibrium phase.

That’s actually exactly why I put that word in quotes. I hope that shows up in the rest of that section. I’m aware there’s no goal or mechanism behind evolution, and that it ultimately ensures nothing. What I was trying to do is explain why the fact that people with disabilities are surviving does not run contrary to evolution or mean that it has stopped or will stop.

Any observer of popular culture can attest to the fact that evolution has reversed itself. Pardon my elitism.

Probably a better question would be: Have humans stop speciating? Genetic drift and evolution of certain traits within a species are always going to occur. But a widely dispersed species, like H. sapiens that does not have geographically or reproductively isolated populations will tend to exist as a single species. This is contrary to what our lineage has experienced in the past-- where it was comon for more than one species of the genus (Homo, Australopithicus, or other) to exist at any given time.

Of course all of this is more than likely to be rendered moot once we start engineering our genes to the point that certain individuals may not be able to mate and produce fertile offspring without manipulation of the egg and/or sperm in the lab.

To say that people predisposed to have large families are more successful at propagating their genes is true, if you look merely at the first generation.

In my experience, large families skip generations. My grandmother has six children (none of whom are planning to have more children) and six grandchildren; over just two generations, the family is not significantly larger than average, and this is without the influence of death or genetic disease. All of her children were reluctantly convinced by their spouses (from small families) to reproduce. On the flip side, single children are the only people I have met who actually want large families – the ones I’ve spoken to usually intend to have four to ten kids.

Stepping away from the anecdote. Ahem. Since 1970, the average number of children has dropped from 2.5 to 1.8 ( http://www.ericfacility.net/ericdigests/ed256475.html ). This would not be possible if people from large families were genetically predisposed to also have large families, since we’ve all seen that two-child families remain quite popular. (IE, it’s not eight kids or none, there’s something of a distribution going on.)

Even in communities where there is not adequate health care or education for the majority, family sizes are shrinking. In many asian and latin american countries, the average family size has dropped from six children to three in the past 25 years ( http://wildcat.arizona.edu/papers/old-wildcats/fall95/August/August23,1995/18_2_m.html ).

Fertility is genetically influenced, true, but it seems that personal preference is far more dependent on environment. And believe me, large families take away a lot of the appeal of having any kids, let alone six of them.

On the issue of intelligence, believe it or not, as a species we continue to become more intelligent. http://pespmc1.vub.ac.be/FLYNNEFF.html

“For one type of test, Raven’s Progressive Matrices, Flynn found data that spanned a complete century. He concluded that someone who scored among the best 10% a hundred years ago, would nowadays be categorized among the 5% weakest.”

Not a complete quack. He got a few pages in my psych book (although that only proves that he’s a popular quack :rolleyes: )

Punctuated equilibrium does’t postulate or required reduced rates of evolution. The concept refers to rates of speciation, not rates of evolution. Humans may indeed be within an equilibrium phase. That doesn’t in any way suggest that evolution isn’t occuring just as rapidly.