This first part is largley in response to hramyaegr, with his arguments paraphrased in italics:
A great many people mistakenly believe that natural selection implies that it only takes place if they who are perceived to be less valuable or somehow deficient are removed from the gene pool.
Natural selection DOES only take place when individuals that are less suited to their environment are removed from the gene pool.
If people with trait X who would otherwise die are helped to survive by people without trait X, that's natural selection.
No, this isn't how things work. The population as a whole does not drastically shift behaviors. If dominant trait X begins to develop in a population, and the affect of this trait is that people with trait X need to be cared for by people without trait X, some people without trait X will care for them, and some won't. Suppose we assign the label “trait Y” to the gene that makes you care for those with trait X.
If the people with trait Y are caused to overburden themselves and consequently die, that's natural selection.
Yes. If trait Y (caring for people with trait X) is a survival advantage, the people with trait Y will come to dominate the gene pool. If it isn't, they will be gradually removed, as will the people with trait X because they don't have anyone to care for them.
If the increase in population from the survival of people with trait X overburdens the system so it can no longer support the population and it consequently dies, that's natural selection.
No, this isn't how things work either. Environments do not have a specific capacity, beyond which massive dieoffs suddenly occur. If the population begins to exceed the environment's ability to sustain it, resources will become scarce. Suppose food becomes scarce. People will begin to die from hunger until the population has been reduced below the level of the environment's ability to support them. The ones that die will depend on which genes are better suited to deal with the situation, thus natural selection.
If people with trait X breed more than people without it and eventually dominate the population, that's natural selection.
Yes. But this will only happen if trait X allows those with it to better survive in the environment. If trait X is impotence or total brain death, it will probably never become dominant in the population.
If you have trait Y and help person with trait X, and do not breed because of it, that's natural selection.
Yes. Trait Y will eventually be wiped out, as will trait X, if people with those two traits are less likely to reproduce.
The issue addressed in this
node is whether or not natural selection is now acting upon us. If a group of
identical pink bunnies have a total of one gene, and it is exactly the same for all of them, and they
mate for
life, always producing two
offspring, and there is sufficient,
identical food to sustain them and there are no
accidents,
violence, or
enmity in this bunny world, no natural selection will take place. Natural selection only ceases to act if the gene pool remains
static -- that is, if everyone reproduces equally.
Obviously, this isn’t happening. Our collective gene pool is continuing to change, and always will be. However, we have greatly slowed the effects of natural selection through the use of
technology. The range of genes that are
irrelevant toward reproduction is constantly widening. Every new wonder
drug we develop renders a few more irrelevant, reducing the
diversity of the population and making us more like those pink bunnies. There are too many raw
variables for us to ever reach pink bunny status and totally stop natural selection, but we have slowed it... for now, at least.
Lith: As far as the
obesity scenario is concerned, it would become prevalent in the short term. In the
long term, natural selection would undo this "
alien mind zapping" or whatever caused women to become attracted to obese men, because obesity puts you at higher risk for
heart disease, and heart disease prevents you from passing on as many
genes.