Why are there so many species of most living beings but only species of humans?

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Why are there so many species of most living beings but only species of humans?

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In the past there used to be other species that, arguably, could be called humans. Neanderthals, denisovans, closely related hominids like that. They have gone extinct, but as of yet no one is completely sure why. Some people guess that we (*Homo sapiens*) killed them all off, but there is evidence that there was a little interbreeding, so some guess that we coexisted and they all died for some other reason.

This is less a question about biology and more about human categorisation. We see quite a lot of distinction between ourselves and our nearest relatives (apes), in no small part because we’re extremely familiar with ourselves and the differences between us and apes are a pretty big deal as far as our priorities are concerned. When we compare, say, a red fox and a grey fox (which are from entirely separate genera – *Vulpes* and *Urocyon*), the differences don’t seem all that significant to us. They have a similar shape and similar enough behaviour as far as we care, so we dump them in the box labelled ‘fox’. Most of the time we don’t really care which kind of fox a fox is. Most of the time we care quite a bit whether something is a human or an ape!

(In fact, many of those categories are specific to a particular language, and things one language considers ‘the same animal’ may be quite separate to speakers of another language. Japanese, for example, has no one word for ‘otter’ – it has *kawauso* for river otters and *rakko* for sea otters.)

It *is*, however, reasonable to ask why there’s only one extant species in the genus *Homo* (which humans are in), when other genera have many more species. This is in large part because humans have outcompeted or otherwise outlasted our nearest relatives, and other species that are conceptually closer to us than living apes are all gone now. It’s also in part because genera are *also* human categorisation tools, and as much as they’re intended to be independent of human bias, we don’t always know what should be in the same genus and what should be in separate genera. It’s not infrequent for genera to be split (or merged!) after taking another look at them. Really, the criteria aren’t all that straightforward, and it’s not uncommon to come across situations where there’s no clear line at all between one species and another or one genus and another. What counts as ‘one kind of living thing’ versus ‘another kind of living thing’ ultimately is a purely external categorisation decided on by humans, even if the differences those categories are based on are real differences.

There aren’t. There are breeds of dogs but only one species of dog – canine

Same with every species – its what defines a species.

And if you mean breeds – there are very few mammals with multiple breeds. And most of those are human engineered thru purposeful cross breeding (horses, cows, pigs, chickens, cats, dogs, Guinea pigs, etc.)

There are seven layers of taxonomic classification of creatures :

https://basicbiology.net/biology-101/taxonomy?amp

The narrowest is species.

It’s also possible you’re misnaming groups as “species” when those words are really larger classes of organisms in the upper levels of Domain, Kingdom, Phylum, Class, Order, Family, Genus, and finally most narrow term: Species.

So insect for example is a “Class” under which there are orders, families, genus’ and then species.

Humans are a species “sapien” of the genus homo, family hominid, order primate, class mammals, phylum chordata, kingdom animalia, domain eukarya…

From phylum up to domain, humans and insects share the same categories…

It’s easier to check out the charts in the link…

There were others. We absorbed and/or killed the others.

There are neanderthal genes mixed in with the cro-magnon.

There are two things humans are really good at: having sex with anything that isn’t up on the trees fast enough – and killing anybody who is “not one of us”. As a result, other human species have either been absorbed into the general gene pool (like the Neanderthals) or simply killed off (most of everybody else).