No, there are three (or possibly one) species of human on Earth, but definitely not two.
We tend to think of the closest relatives of Homo sapiens, the two members of the genus Pan, as being non-human, or sub-human. But when we try to provide an objective reason why, we uncover an uneasy truth. We are very similar to both Chimpanzees and Bonobo Chimps. There are striking similarities in our brains, internal organs, diet, behaviour, skull structure etc. We tend to emphasise those differences we do find because we want to be unique. We notice the differences between chimps and our own species more than the differences between, for instance, dolphins and porpoises, or finches and wrens, because we know ourselves so well.
You might think this is just a sort of reverse sentimentalism, that I am saying we should be kinder to animals by admitting we are animals too, or emphasising broad similarities just to make a smart-aleck point. But what I am talking about is not just a subjective matter of listing superficial similarities and differences.
Scientists studying the genomes of the members of the genera Homo and Pan have found that we are very closely related. In fact, if such a close similarity were found between any other two genera, they would probably be merged as a matter of course without too much fuss. But we are hesitant in the case of Pan and Homo precisely because it goes against our subjective feeling that we are not "mere apes".
Here are just a few articles citing genetic studies that find that both Pan troglodytes and Pan paniscus should be part of genus Homo (or alternatively, that Homo sapiens should be moved to genus Pan):
- National Geographic: Chimps Belong on Human Branch of Family Tree, Study Says
- Science Daily: DNA Demands Chimps Be Grouped In The Human Genus, Say Wayne State Researchers
- Guardian: Closer to man than ape
Links to the actual academic studies:
- Implications of natural selection in shaping 99.4% nonsynonymous DNA identity between humans and chimpanzees: Enlarging genus Homo
- Sister grouping of chimpanzees and humans as revealed by genome-wide phylogenetic analysis of brain gene expression profiles
So the answer to this question comes down to the definition of "human". If you define humans as members of the species Homo sapiens, then by definition there is only one human species. Your question can't mean that because then it would be circular and meaningless. If you consider man to mean "a member of the genus Homo" (which means 'man' in the sense of 'human'), then there are, arguably, three living, human species on the planet: Homo sapiens, Homo troglodytes and Homo paniscus. But there definitely aren't two.
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Edit: I wrote this answer two years ago. Since then, many people have commented (thank you) and about half of those who have commented have misunderstood what I am saying. I am most certainly not saying that Homo sapiens, chimpanzees and bonobo chimps are one species. I am saying that, while they are traditionally grouped into two separate genera (genus Homo and genus Pan), some scientists consider the two species of Pan to be so close to Homo that the three species really should be in the same genus together. Since Homo is means human, you could potentially treat the three species as different species of human.
Thank you to all those who have helpfully pointed out that we can’t interbreed with chimpanzees or bonobos and therefore aren’t the same species. If you have read the above paragraph and understood it, you will realise that this is not relevant as I’m not saying we’re the same species at all. If you have just read this and are tempted to write a comment reiterating the textbook definition of a species, then you have not understood the question and I will ignore and probably delete your comment.
I am also aware my answer does not reflect the common, intuitive understanding of what a human is or how genus Pan relates to this category. That’s the point. Faced with a question that is bizarre to the extent of almost being incomprehensible, I felt that there were two options: to state the common-definition consensus (Homo sapiens is the one and only human species) or to attempt something a bit more provocative and hopefully thought provoking. I thought the latter would have more chance of adding value to Quora.
I hope this makes it a bit clearer to those who didn’t follow my line of reasoning in the main answer.
And finally, since someone asked for it, here is a clarification of primate taxonomy:
Class: Mammalia
Order: Primates
Superfamily: Hominoidea (Apes - excludes monkeys, tarsiers, lemurs and lorises) [Hominoidea means ‘like humans’]
Family: Hominidae (Great apes - orangutans, gorillas, chimpanzees, bonobos and humans) [Hominidae means ‘like humans’]
Genus: Homo (‘human’, our genus) and Pan (chimps, two species). Or, as I have suggested in my answer, one genus containing three species.
Species: Homo sapiens (humans), Pan troglodytes (chimpanzees) and Pan paniscus (Bonobo chimps). Or, as I have suggested, perhaps Homo sapiens, Homo troglodytes and Homo paniscus.
In order to be classified as a species, the members of the group have to be able to interbreed to produce offspring. That means that there were, at one time, probably three species of “humans” - the Neanderthals in Europe, the Denosivans in Asia, and the homo sapiens - ie. modern humans. We know now that modern humans, the sole surviving members of the species, can carry trace amounts of either Neanderthal and/or Denosivan genes - which tends to indicate interbreeding and hence membership in the same species.
A species is the most exclusive taxonomic classification - hence the requirement to be able to interbreed and produce offspring in order to remove any doubt. Such is not the case with humans and apes - I will never be a monkey’s uncle.
There is a complete examination and answer to this question at:
The Truth About Human Species <http://www.aoi.com.au/bcw/Human/...>.
What is explained there is that all the "species" of human described now or in the past 5-million years or so are all one species (they could potentially interbreed). These "species" are best described as Land-races (eg Homo "Neanderthal").
It's also explained there why humans differ essentially from the higher-ape species. Humans have 23 pairs of chromosomes, all the rest have 24 pairs.
So while there's only one species of human alive on the planet now, there is another whose genetic legacy still lives on in us.
There is currently only one species of the genus Homo that is still living, H. sapiens. These are anatomically modern humans, and the majority of our DNA are the same as all others of the species. There used to be other human species, such as H. s. idaltu or H. neanderthalensis. But as for now, anatomically modern humans are the only human species on earth
There is only one as of now. Long ago during the Quaternary period there was several more; Homo Sapiens-which can be divided into subspecies as Homo Sapiens Sapiens, Neanderthal, and Densivonan; Homo Erectus; Rhodesia Man; Homo Florienses; and Homo Habilis. Over time these groups were gone and we are left with just Homo Sapiens Sapiens. However, if you’re not pure African there’s a chance you have some Neanderthal or Densivonan in you.
Seriously, speciation occurs so gradually that it's impossible to pin point when it occurs. You can't just take a bunch of wolves and point at them and say "oh 2 of these 10 wolves have evolved to be dogs". It doesn't work like that. Traits appear slowly over many many generations.
It could happen that humans evolve to be 2 separate species 10,000 years from now. That process might already be occurring. However, you cannot point to certain humans and call them non-humans. It doesn't work that way.
You'd have thought by now (given all of the advances in genetic science) that somebody would have sat down and started the long hard slog of creating a more "reality-reflecting" system than the binomial Latin system, which was begun even before the birth of Charles Darwin. Systems of classification exert a disproportional gravity on the area of study that they are applied to, and it feels as if the binomial system gives rise to a lot of binary thinking in an area (evolution) that is exponentially not a binary phenomenon at its very core. In that context, such questions as this sound like the question of how many angels can dance on the head of a pin.
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