Some people have argued they were a subspecies instead for this reason. But I didn’t want to get into that because it doesn’t change the overall picture. Whatever you want to call them, they’re far more distinct than human races today. Races aren’t distinct enough to be labeled at any taxonomic level that’s used to describe distinct taxonomic groups within non-human species. This didn’t stop early racist thinkers from trying, but the picture has become clear after more than a century of scientific research on the topic
But yeah the difference between species and subspecies can be a bit fuzzy as well. We used to define species such that they couldn’t interbreed, but then we learned that lots of clearly distinct species can interbreed too.
In some cases, species can be maintained by natural selection rather than reproductive barriers. A classic example is oak trees. Many oak species can easily cross with their close relatives and do so very frequently. However, since each species is adapted to a different ecological niche, the hybrids end up in ecological no-mans land, doing worse than either pure parent in their respective habitats. Because of this, they rarely reach maturity or contribute much to the gene pool, and the species remain distinct.
However, in some very specific environments they can, and this has been very important for oak evolution since it allows entire clusters of species to occasionally share genes, aiding in their evolution. This is thought to be one reason why oaks have adapted to almost every temperate treed environment in North America.
Some people have argued they were a subspecies instead for this reason. But I didn’t want to get into that because it doesn’t change the overall picture. Whatever you want to call them, they’re far more distinct than human races today. Races aren’t distinct enough to be labeled at any taxonomic level that’s used to describe distinct taxonomic groups within non-human species. This didn’t stop early racist thinkers from trying, but the picture has become clear after more than a century of scientific research on the topic
But yeah the difference between species and subspecies can be a bit fuzzy as well. We used to define species such that they couldn’t interbreed, but then we learned that lots of clearly distinct species can interbreed too.
In some cases, species can be maintained by natural selection rather than reproductive barriers. A classic example is oak trees. Many oak species can easily cross with their close relatives and do so very frequently. However, since each species is adapted to a different ecological niche, the hybrids end up in ecological no-mans land, doing worse than either pure parent in their respective habitats. Because of this, they rarely reach maturity or contribute much to the gene pool, and the species remain distinct.
However, in some very specific environments they can, and this has been very important for oak evolution since it allows entire clusters of species to occasionally share genes, aiding in their evolution. This is thought to be one reason why oaks have adapted to almost every temperate treed environment in North America.