With all of the medical advances in healthcare, have humans simply stopped evolving? We don't live in a "survival of the fittest" world anymore. There are a lot of genetic problems that we can fix with surgery - getting our wisdom teeth removed is practically a guaranteed surgery now, braces correct dental problems, medicine maintains diseases - but once we reproduce those genes are still there in our children, and so we are keeping weaker genes in circulation. I have horrible eyesight without my contacts and would not have lived long had I been born hundreds of years ago so I am glad we've come a long way, but I'm just wondering if by making all these advances are we really weakening our genes to the point where it's impossible for us to evolve further as a species.
The answer I am sure is No. Having said that of course modern medicine and technology are having an effect on the "direction of travel". It is important to remember that the rate of mutation of the human genome with time is either not altered by our modern lifestyle or possibly even increased due to chemicals and nuclear materials. Thus there is no reason to think that over time we will not slowly be evolving/changing. The real question therefore is how does modern medicine affect the pressures for positive and negative selection, and at the moment I think it is impossible to answer that. To paraphrase desiderata:-
And whether or not it is clear to you,
no doubt our genome is unfolding as it should.
humans are definitely still evolving - just look at the reports of immunity to HIV in Kenya. We discuss the evolution of modern humans in a previous post (http://www.askabiologist.org.uk/punbb/v php?id=899).
For natural selection there needs to be variation and selection. At the moment in the "Developed world" lots of people are surviving despite mutations and genetic conditions that might be disadvantageous. This increases the amount of genetic variability, which may be worked on by selection processes in the future. Keep in mind that we cannot tell how selection pressures will be brought about in the future, so we really do not know if a trait might be benficial. Sickle-cell anaemia is a good example of a genetic disease that can confer an advantage against malaria in the heterozygous state. What may seem bad under one set of conditions may prove useful under another set...
To add to David and Paolo's points, it's important to remember that natural selection will favour any trait that leads to the production of surviving offspring. For most species, this means traits that help an individual survive to reproductive age and attract a mate once adulthood is reached. This was also true of humans, in our evolutionary past. At least in developed countries, however, the vast majority of individuals survive to adulthood and (because all developed countries are more or less monogamous) most of them can be expected to find a partner with whom they can have children if they so choose.
This does mean that the usual evolutionary pressures have been greatly relaxed, and in fact I think it's hard to avoid the conclusion that the people who have the most children in developed countries are simply the ones who WANT the most children. I wouldn't care to place any bets on whether or not some individuals are genetically more inclined to produce children than others... but if such genes exist, they may now be the predominant targets of natural selection.
Something else to be aware of: evolution =/= natural selection. In other words natural selection is not the only process that affects evolution. Genetic drift is a process by which a genetic variant randomly changes it's requency in a population; in other words, a certain mutation (e.g. purple eye colour) is not affected by selection pressures and increases or decreases in abundance unpredictably. This is therefore more significant where selection pressures are weak or absent, such as many parts of the human worls today.
Some evolutionary researchers even think that genetic drift plays a bigger role in all evolutionary change than natural selection does. For example, drift can accumulate large amounts of mutations, which are neutral under the prevailing conditions, but which may become not so neutral should the environment change and selection pressures increase.
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