The fact that some people leave many descendants while others do not does not necessarily imply the existence of strong selective pressure, particularly selecti

The fact that some people leave many descendants while others do not does not necessarily imply the existence of strong selective pressure, particularly selective pressure for genetically heritable traits. For example, it could be mostly random, resulting in genetic drift that has essentially nothing to do with external environmental factors. By most definitions genetic drift is not natural selection, because it doesn't select for any particular attributes in the species, outside of preserving basic functional requirements (e.g. members of the species must be able to reproduce at a reasonable rate). "Desire to have children" is a good example of something that does not obviously select for any particular genes. Many people who don't have children (or have only one) simply don't feel they can afford it, or (e.g. in China until recently) live somewhere where having extra children is a liability; while money is indeed heritable, selection against the poor or legally disadvantaged is not natural selection. Similarly, selecting for people who believe in a particular religion that encourages reproduction, etc. These things are not correlated with genetic markers to begin with so this "selective" process will just lead to more drift, or (if the population shrinks sufficiently) result in bottleneck events that lead to even more genetic homogeneity without selecting for any useful traits. I'm not saying sexual selection isn't a thing, incidentally--but I am saying that there's very little evidence that sexual selection is the primary driver of whether humans reproduce. This is qualitatively different from "real" natural selection, which requires a combination of any or all of: significant external stressors, significant untapped resources, a lot of generations, and a high population or mutation rate. We can see that humans are not under especially significant selective pressure when we consider that despite huge death tolls and a very strong negative effect on ability to reproduce, it will take a very long time (IIRC, on the order of 1000 years) before a large majority of people in any area of the world are naturally resistant to HIV.