Cecil did a column a while back that basically said humans are still evolving but I have this followup…
Nowadays most people in the western world will probably wind up with around 2.2 kids.
Does natural selection/evolution stop working in this environment? Say I have a genetic mutation that makes me impervious to communicable diseases can my genes spread throughout the population if I/my descendents only have small families? (barring some catacylsmic virus wiping out everyone else)
It would depend how much inbreeding is in your family.
There will be selection as long as different people have different numbers of children and the number they do have is at least partially determined by heredity. If the variation in the number of children is low or if the variation due to heredity is low, then the pace of selection will also be slow, but it will still be there.
Having a smaller size family only changes the speed that changes take place. Changes WOULD take place, just at a slower pace because it would take more generations for a trait to become more common in the population.
Sure it still works; for example, it’s quite possible those kids are the result of infidelity on the mother’s part. Thereby passing on genes for good looks or the capacity for good seduction ( from the lover ) and the genes for less than total marital fidelity ( from the mother ).
Also, many or perhaps most conceptions end in miscarriage; that’s an awful lot of natural selection going on right there.
People still die from disease, so yes. It wouldn’t spread as fast in the old days where people being wiped out like that was more common, but it’ll spread.
Then you have to consider is human choice natural selection?
We are influenced in our effective attempts to procreate by complex behaviors, social habits, laws, and tribal influences, war, plague, pestilence and famine. All of those influence who gets to have those 2.2 children, and how many of those children survive to procreate. However natural you consider it, it is certainly selection.
Tris
Assuming that seduction and infidelity are inheritable traits rather than learned behaviors or responses to the environment.
Put another way: Wilt Chamberlain is said to have slept with several thousand women, and I think it’s safe to assume that he ended up having hundreds of children as a result. Clearly, Wilt Chamberlain was much more evolutionarily successful than the average human male. And at least some of what made him so successful was presumably genetic. If current trends continue, then, the humans of the future will be a lot better at playing basketball than we are today.
And there’s no guarantee that beneficial mutations spread, even slowly. If you have a new mutation that makes you immune to all diseases, but you also happen to be a pathetic loser who can’t get laid, then your amazing new disease-proof genes won’t spread anywhere.
As long as people are reproducing, and there are natural selective pressures, then yes, natural selection does work.
As Der Trihs noted, one selective pressure is that once conceived, you need some kind of working system to get born/be viable at all. There are also still some genetic defects that make it very unlikely that you’d live long enough to reproduce.
But that’s not all; there are people who just don’t care about reproducing, or just can’t find a mate, or for whatever reason don’t reproduce. Other people might reproduce but don’t take good care of their children to the point that their children won’t have as good a chance to reproduce (they may leave them, or die, or even kill them). Some of all that will be influenced by genetics. Hence, evolution occurs.
In part they certainly are. Social skills have a known genetic component, as probably does infidelity ( there’s even a theory that women have orgasms in part to make cheating more efficient; it increases the chance of conception and is more likely with a lover than a husband ). Good looks are obviously heavily genetic. At least in part everything ( or nearly so ) humans do and are is at least partly genetic.
I’ve never understood why there’s so much speculation about the reason for female orgasms, when the simplest explanation is that they have them for the same reason that men do: People who enjoy sex are likely to have more children.
Because it’s unusual; the females of most species seldom if ever have orgasms. So why do women?
Of course it still functions. Why wouldn’t it? Natural selection isn’t something that can be “turned off”, unless it somehow becomes possible for any and all heritable variations to be equally beneficial. In which case, there will still be genetic drift, so there will still be evolution.
For any species, “unique” traits will take much longer to filter through the population, particularly a large population, assuming they do at all. There are many factors to consider, including just how the mutation benefits you, how (or if) it benefits your offspring when heterozygous (as it necessarily must be initially), how likely you are to find a mate in the first place, the size of the population, etc. In general, however, unless you and your descendants are particularly fecund, your super-special genes are going to be limited to a very small population, relative to the total size of humanity. So if we are limiting the discussion to 2.2 offspring per generation, it’s going to take a very long time before your mutant genes qualify as an adaptation. Odds are much better hoping for that cataclysmic event, really…
The point here is that adaptations do not result from unique individuals. They result from several individuals possessing beneficial variations of a particular phenotype. Those whose traits vary in directions which best benefit them in a given environment are, in turn, more likely to pass those variations on to future generations. In a very small population, such a unique individual might have more genetic influence, but in a large population, such as that of Homo sapiens, said individual’s genotype is more likely to get lost in the background noise of genetic mutations. And, you may well be immune to disease, but what happens if you get hit by a bus before you reproduce…? And there’s always the possibility that your immunity-gene mutates into either something detrimental or neutral within a few generations.
The average woman will have something around 2.2 kids - actually that number varies from place to place, and I think it’s a bit high for the Western World Average. But still, we’re talking about an average.
Some women have no children.
Some women have one child.
Some women have two children.
Some women have three children.
Some women have four children, and so on.
And the same is true for men, with some fathering no children, some fathering one child, and so on.
Right there is a mechanism for natural selection. In an age when we can to a large degree choose how many children we have, what leads some men and women not to reproduce (some of the reasons are under their control and some aren’t, of course), and what leads others to have large families?
I pity the woman who gives birth to that 2/10 of a child. 
In all seriousness, a lot of the changes in evolution do take hold due to cataclysmic events. If all but a few dozen members of a species die off, or more likely a few dozen are somehow isolated from the main gene pool, then their descendants are going to have a gene pool based on those original few dozen, including any novel or unusual genes those few dozen happened to have. Once the gene is established in the subpopulation, they might eventually meet back up with the main population and spread the gene back into them, or the original main population might go extinct (possibly by competition with the new population), or they might both stick around but become different enough that they’re separate species.
Indeed. Of course, the founder effect cuts both ways: you may get a population with super genes, but you can also get a population with decidedly less than super genes. See, for example, the inhabitants of the Pingelap atoll, wherein because of a typhoon that wiped out all but 20 individuals a couple hundred years ago – one of which was a carrier for achromatopsia – the frequency of carriers for the syndrome in that population today is about 30% (whereas it’s only about .003% in the U.S.).
So, small populations can definitely increase the rate of change for gene frequencies in a population, but those changes are not necessarily adaptive; such increased frequencies are often the product of genetic drift rather than natural selection.
This doesn’t really have anything to do with the question, but I’m tired and I’m going to post it anyway. There are also mechanisms that can lead to “bad” traits sweeping through the population. Let’s say that you have a mutation that gives you the ability to seduce women at a glance. Obviously, this trait is going to spread rapidly to fixation throughout the population.
Now let’s say that right next door on the chromosome to this mutation, so close that recombination is rarely able to separate them, is another mutation that gives you, let’s say, a mild but chronic headache. This is a trait that, by itself, would be selected against, because you’d always be saying, “Not tonight, I have a headache”. However, because of its physical linkage to the seduction mutation, you don’t get one without the other. The strong positive selection of the seduction allele far outweighs the weak negative selection of the headache allele, and so soon you’ve got a whole population of seductive but slightly headache-y men.
Selection only selects for traits that are more likely to reproduce, not necessarily what you might think of as better. A gene that makes you more resistant to disease is going to be a small difference to Westerners, where disease is low on the list of causes of death of fertile people. But a gene which makes it easier to deal with lots of electronic information would be just the thing to help with online dating.