Sapiens by Yuval Harari defines "human" as "any member of the genus Homo". I don't know how common or accepted this definition is.

It could become problematic if, as has been suggested, some or all of the other great apes are reclassified as Homo rather than Pan, Gorilla or Pongo.

I think that this is the usual definition of "human", but I also think that it doesn't agree with the layman definition of "human". https://en.wikipedia.org/wiki/Human

For a layman, an "human" is a "modern human", i.e. "Homo sapiens sapiens", i.e. me.

There are two difficult problems here. The first is how to classify animals species (including humans, whatever it means). The taxonomy classification is somewhat arbitrary. It's very useful for discussions between biologist, but arbitrary.

For an easy example, what is a kingdom looks like an easy question, but https://en.wikipedia.org/wiki/Kingdom_(biology)#Summary

Currently Homo, Pan, Gorilla or Pongo are different "genus" of the Hominidae "family". (I hope I got all the notation correctly.) The genus is somewhat special, because it's written in the name of the specie, but we could have agree to write the family in the name two. We could have been "H. H. sapiens sapiens" and chimps could be "H. P. troglodytes"

The second problem is that we all agree that the sentence for killing a "human" should be different of the sentence for killing a cow or a pig. But the decision of what "human" means in that sentence is a political one, not a scientific one. Should we consider killing any great apes as bad as killing me? What about other apes? Why? Why must we use the taxonomy classification? What about whales and dolphins? Octopus?

> We could have been "H. H. sapiens sapiens" and chimps could be "H. P. troglodytes"

Tangent, but if we ever genetically engineer some eldritch horrors, I vote to classify them as "H. P. lovecraft".

There's a traditional of using Latin names for species classification, so maybe H. P. Lovecraftus

True they are genetically different but that's not the definition of a 'species'. There is a level of politics in biology over what constitutes a species and what does not.

Technically a 'species' is something that interbreeds but does not breed with members outside of it's species and mating produces reproductive offspring. (at least this is the old mayr definition that everyone uses)

The problem is that neanderthals and humans matings produced viable offspring. So is 'neanderthal' a species or not?

The same issue is a problem with the Galapagos finches, which are the holy cows of darwinian genetics. By Mayr's definition they should not be able to interbred and produce viable offspring. However, apparently they can interbreed and therefore are not technically different species.

No one in science want's to badmouth the masters, so Darwin's theory of Galapagos finch species will quietly be put back in the Victorian cabinet while we invent a new 'genetics' based theory of 'species' that makes everyone happy. However, life is not easily classified. Viruses? Species? Bacterial plasmid replication?

There is a lot of politics in the life sciences. Naming a new species or having your name on a species is a big deal. It reminds me of Cope/Marsh and the dinosaur finds (https://en.wikipedia.org/wiki/Bone_Wars) of the early 20th century. They both screwed up the identification of many species so that they could out publish the other and left the mess for future scientists to clean up.

My feelings on this is that we still don't have enough evidence about the genetic makeup of humans to really make any conclusions on anything. Example: What is the blood type in the reference sequence for the human genome?? We know that there is A, B, A/B and O which represent 4 different genotypes (an AA sequence, a BB sequence, an AB sequence and a missing sequence from both alleles).

If I sequence a neatherthal with blood type A and a human with blood type O, are we genetically divergent?? How can you come to this conclusion unless you know the plasticity of each genome. (i.e. I can't identify a nucleotide change in blood type gene for a type O human because the gene is absent)

It looks like most of the research has been on mtDNA which is passed from mother to child. If we can't find a mtDNA match, it might just mean that there is no maternal linage that can be traced back to that sequenced individual. (i.e. all the children of that mother died out at some point)

Different species? That's a question for politics imho. I personally think that life shuns classification. BTW sorry for the ramble :0

Then you have ring species[1] that blow a nice big hole in the interbreeding based definitions of species.

Species and race are vague terms we use for convenience. That's all. I think keeping them vaguely defined is a feature not a bug, because it could help prevent people assigning too much weight or meaning to them. If people get the idea that race and species can be precisely defined, then maybe they can be measured? Maybe we can use that to derive tests or policies? But trying to precisely define race and species is futile, like trying to put light in a box. I'd rather knowingly and consciously keep the ambiguity, to remind myself that the terminology isn't the reality.

[1] https://en.wikipedia.org/wiki/Ring_species

One definition of a "market" is people with the same needs who reference each other (i.e. talk to each other). This transmission of information ("word of mouth") is important for marketung [...though perhaps a bit different today, with referencing internet reviews.]

Similarly, the definition of species as individuals that breed with each other has importance for transmission of genes. By this rationale, transitive gene transmission makes ring species a "species".

A biologist told me that species are defined, not by theoretical interbreeding, but by actual breeding...so that a single species divided somehow in different environments, is now two species, even when no genetic change has occurred.

By this strange extrinsic definition, the human races were different species before global travel... and now are one.

And that SV hackers who only breed with other SV hackers, are a different species (and the rise in autistism incidence evidences a genetic effect - in a few million years, interbreeding will be impossible!). Similar for classes, the 1% etc.Though there is crossbreeding in practice, so at most these are ring species.

> BTW sorry for the ramble :0

No, that is the best kind of ramble. Thank you for the interesting and thought-provoking comment!

No, it's just logic. Inclusion of populations in species depends on breeding ability. And there's no way to test that for fossil individuals vs each other or vs modern humans. So they can't be classified as the same species, or part of a species ring.

Your answer gives no explanation beyond "because they are not humans". How do you know that?

Because we have extensive samples of the Neanderthal genome extracted from bone fragments, and before that from morphological studies of the Neanderthal skeleton which display far greater differences from humans than any differences in skeletons between human races. Even 18th Century observers were able to see that.

Yes there is no one universally agreed definition of species, but Neanderthals were vastly more different from living humans than and differences between living human populations.

BTW is there a good comparison for how big the anatomical differences are between Neanderthals and modern Europeans, compared to the differences between modern Europeans and modern, significantly distinct populations such as Congo pygmies?

https://en.wikipedia.org/wiki/Congo_Pygmies

(Anatomic differences are perhaps not as important as cognitive and psychological differences, but the latter are very hard to find out about extinct populations.)