There are many different species of mostly the same animal… That differ only in the slightest details…
But humans despite evolving separately for a very long time are still the same species regardless of the race.
In: Biology
Species are usually defined as organisms that could breed and positive viable offspring that can itself procreate. Humans can obviously do that despite our differences, so we’re definitely the same species.
However, it can get tricky. Horses and donkeys can produce mules that are sometimes fertile. On the other end, some species are genetically perfectly able to procreate, but don’t with certain members who have different pigmentation out different mating calls (eg grasshoppers). If they could breed but don’t, are they the same species? I guess it depends on how you want to define the term and for what purpose.
There used to be different human species. Ours outcompeted them and they died out. The humans that exist now have only been diverging for no more than 90,000 years, and still interbreeding with each other for a significant chunk of that time, with the exception of certain isolated groups. There hasn’t been enough time or opportunity for Homo Sapiens to split off into multiple species.
It’s not the slight external details that mark a species but genetic or physical incompatibility with other groups. Those happen over a long time and can partially depend on the luck of the draw.
A simple definition is the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring. But it’s really useless in some cases, for example Polar and Grizzly bears can and do produce fertile offspring but they are very different in habit and appearance and it’s far more sensible to name them as separate species.
Generally speaking a population with significant enough genetic, physical or habitual differences that normally breeds independently is regarded as a separate species even if they have no trouble interbreeding with another species.
Humans are very genetically similar and almost no populations have really had enough time to evolve seperately. The whole of Afro-Eurasia is connected and there has always been at least some flow of genes so even relatively isolated peoples like the Khoisan have some cosmopolitan genes.
Australia was probably always connected to the mainland a little bit by the Torres Straight Islanders. The first Americans arrived about 13,500 years ago and were cut off by the seas rising at the end of the ice age, but there was another large prehistoric influx of Inuits from Siberia about 5,000 years ago and some evidence of contact thereafter so for both native Australians and Americans the separation wasn’t perfect and since humans are slow growing animals 13,000 years or even 50,000 years aren’t so long as they might be: Evolution is measured in generations rather than time which is about 26.9 years for a human, whereas it would be 12 weeks or so for a house mouse.
There is no single definition of species that applies to all groups of life, it’s just a sensible category. For example, there are way more bacteria out there evolving more quickly than we could ever categorize them, so when we work with them we sometimes use “operational taxonomic units” rather than species. These can be defined based on a similarity threshold, like everything of 97% sequence similarity being grouped together.
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