Natural selection means some get left behind. Humans work very hard to avoid that.
And you believe that none are? When did the death rate for those under 80 reach zero? I some how managed to miss the announcement! [/sarcasm]
Of course humans work to avoid that. That doesn't make them 100% successful at it. Plenty of people die before or without reproducing, and those people were "selected" against whether as a result of disease, war, bad luck, lack of desire to have children, or their own stupidity. We are not as heavily culled by "natural" events as we might be, or once were, but that only means that we've increased our genetic diversity.
Some of those genes have demonstrable down sides, but it is common in evolutionary studies to see a widening of the gene pool when selection pressure is reduced. This is a natural part of evolution as the species begins to differentiate to take advantage of different ecological niches. Furthermore, there are most definitely internal selective pressures at play as well.
Western countries have become nuclei of successful people, with hot bed (like silicon valley) acting as concentrators of certain phenotypes (the stereotypical borderline and high functioning autistics that are the engine of computing progress). That those traits may have been an evolutionary disadvantage in pre-computing days does not change their current value today, or their current effect on those individuals chances of reproducing.
Diabetes, cancers, gastric disorders (Celiac, e.g.), endometriosis, fibromyalgia, and any number of other increasingly common disorders would contradict that
1. Diabetes is no longer fatal, and many who have the more mild form could control it without insulin if they just ate a healthier diet.
2. Cancer has always existed for those who live long enough
3. gastric disorders, if not fatal or don't reduce ones chances of reproduction, are not inherently relevant to survival even without modern medicine
4. endometriosis, has also always existed. it can be seen in non-domesticated species
5. fibromyalgia is vague pain. Again, pain by itself is not fatal and does not reduce ones odds of reproducing even in the absence of modern medicine. Especially if it frequently does not occur until one is past their prime reproductive years.
6. poor eyesight has not been a selection pressure in centuries, even before the development of optics or the widespread availability of corrective lenses. Again, especially in those cases where it does not appear until after the person has passed their prime reproductive years. Most people who wear glasses at younger ages do so to correct relatively minor defects in their vision.
7. IVF has risen in prevalence in part due to changes in human culture. Many women who might have been able to conceive naturally in their teens and 20's need IVF in their 30's and 40's because of non-genetic problems, and therefore are irrelevant to the discussion of selective pressures.
Whether that's a gene that results in sickle cell or juvenile diabetes or whatever, that's what I mean by a "bad gene".
Being heterozygous for sickle cell is a BENEFIT if you live in a malaria rich region of the world, so to categorically state that it is "Bad" is myopic. This is exactly the point I've been trying to drive home. The value of a phenotype is situation dependent, and just because it confers no benefit in one situation does not mean it could not under different circumstances. The sickle cell trait spread as widely as it did in African populations in spite of the problems being homozygous for the trait can cause because the heterozygotes were better adapted to frequent exposure to malaria.
Tell a child with leukemia or diabetes that his "trait" is actually beneficial in some way. Tell someone who is badly nearsighted and can't see anything without glasses that his trait is beneficial in some way. Tell the child who is born with a cleft palate that you aren't going to do cosmetic surgery because his trait is actually beneficial.
In the current environment, no none of these are beneficial. However, that does not mean they could not be under the right conditions or when paired with other genes in a different individual. Also, cleft palate is not always genetic in origin. Far more of those who develop a cleft palate have no genetic predisposition and they could have developed the phenotype due to environmental reasons (maternal nutrition, physical trauma, exposure to a chemical that interferes with midfacial development. Furthermore, evolution is not about the individual, but the species. Using the Sickle Cell example again, homozygotes with the sickle cell allele generally die, but their heterozygote siblings survive much better than those who are homozygous for the non-sickle cell allele.
Let the Down Syndrome kids use their beneficial trait to make good lives on their own.
You have obviously never heard of the neurodiversity movement. I've worked with special needs kids and there are some with down syndrome that are quite capable of surviving on their own. More capable than many non-down-syndrome individuals I know.
when you remove natural selection from the process of evolution, evolution no longer works
It is exceedingly arrogant to believe that humans are somehow exempt to selective pressures. As long as reproduction rates are not evenly distributed across the entire human population (ie 2 children per couple, and all children live to have 2 children themselves infinitely), then there will be evolution as some genes become more or less prominent in the overall population. To believe otherwise is to seriously misunderstand the underlying mechanisms of evolution.
No, I really don't care, because that's so far in the past that it was before existing civilizations and thus before current efforts to defeat natural selection that it is completely irrelevant to this discussion.
No it is not irrelevant. It is an example of the loss of an ability that on it's face would be a negative (like the ability to digest lactose or gluten), yet turned out to be irrelevant to the survival of the species. You seem to operate under the false assumption that any loss in evolutionary "fitness" for past selective pressures is an unequivocal negative for our evolution as a species. However, the fossil record of all species is littered with examples of lost traits that were essential during one era, but unimportant to survival later on.