"If humans turn out to be near the Kondrashov limit —that is, if on average every gamete has one bad mutation created during the lifetime of its producer— it is obviously not going to be nearly enough to test a baby for the subset of the few hundreds or so of well-characterized genetic defects"

“The incursions of barbaric pastoralists seem to do civilizations less harm in the long run than one might expect. Indeed, two dark ages and renaissances in Europe suggest a recurring pattern in which a renaissance follows an incursion by about 800 years. It may even be suggested that certain genes or traditions of the pastoralists revitalize the conquered people with an ingredient of progress which tends to die out in a large panmictic population for the reasons already discussed. I have in mind altruism itself, or the part of the altruism which is perhaps better described as self-sacrificial daring. By the time of the Renaissance it may be that the mixing of genes and cultures has continued long enough to bring the old mercantile thoughtfulness and the infused daring into conjunction in a few individuals who then find courage for all kinds of inventive innovation against the resistance of established thought and practice. Often, however, the cost in fitness of such altruism and sublimated pugnacity to the individuals concerned is by no means metaphorical, and the benefits to fitness, such as they are, go to a mass of individuals whose genetic correlation with the innovator must be slight indeed. Thus civilization probably slowly reduces its altruism of all kinds, including the kinds needed for cultural creativity”

“Conceptual simplicity, recursiveness, and formal separation of levels of selection are attractive features of these equations. But, of course, being able to point to a relevant and generally non-zero part of selective change is far from showing that group selection can override individual selection when the two are in conflict. Moreover, even the possibility of devising model circumstances in which a positive group-selection term outweighs a negative individual selection one , gives no guarantee that ‘altruism’ can evolve by group selection: we have to consider whether the population can get into the specified state, and, if it can, whether its present trend will continue.”