This evening I explained what I believe about evolution, how there are no such things as discrete species (by the same logic, there are no such things as races), but rather those are arbitrary labels for a specific populations of living things who can interbreed at a specific time. When visualizing an evolutionary tree, two species alive today will have a common ancestor. Just as those two species are collections of individuals who can interbreed, that common ancestor is not one individual, but it is a collection of individuals who can interbreed. How do we ever get a new species? Think of a manydimensional chart where each dimension represents a gene. The DNA at that position, determining that gene, determines the position on the chart in that dimension (This needn’t even be linear… it could itself be manydimensional). Even if every living thing had exactly the same DNA at a given moment, individuals and offspring will diverge due to random mutation, and the individuals would pull away from each other on that chart. At first, everyone is close enough to everyone else to interbreed. But eventually an individual will be born far enough from another individual they won’t be able to interbreed. (This implies two individuals who cannot interbreed could possibly both still be able to interbreed with the same other individual? If all individuals have same potential genes, but it’s possible for some to not be able to interbreed with each other, is that just a result of particular genes? Presumably certain genes will be disadvantageous or even deadly, but the individual carrying those genes was still born, so its parents are the same species as each other, even if not the same species as the offspring (but that’s highly unlikely to be the case since the parents and children are so close on the manydimensional chart).) That marks a new species relative to the individuals it can’t interbreed with. As time goes on, that separation gets larger, and more individuals are considered a separate species from those further back in time or further away genetically.

But maybe that point about individual genes making the difference is more important than I think, and a child really could be a different species as his parents by virtue of breaking some critical gene that causes an incompatibility with some individuals but not all. In that case, it seems species isn’t measured by a threshold distance separating individuals on that multidimensional chart. Or, perhaps, the distance on the chart determines the likelihood individuals are the same species, but not strictly whether they are or not. Further away individuals are only less likely to be the same species. But that still doesn’t seem to match a universe where a child could be a different species as the parent by virtue of not being able to interbreed. Maybe that’s not the right measure for species. Maybe that random genetic problem preventing interbreeding with the parents is akin to a physical injury that prevents interbreeding. Maybe the individual will never be able to breed, but we can’t use that to claim it is a different species.

As for race, it certainly seems to match the manydimensional way of visualizing species, with none of the problems of sudden new species. I don’t see any corollary for sudden new races. Since race is genetic and species is genetic, it would seem they should have the very similar properties. This makes me hope the second paragraph of implications of the possibility an offspring couldn’t interbreed with the parents is based on a possibility that can’t happen. I’m nervous to google it and find out.