General Question

El_Cadejo's avatar

Are there multiple species of humans?

Asked by El_Cadejo (34477points) October 8th, 2010

A couple nights ago me and my lovely girlfriend were talking and we came around to a particularly interesting conversation. Are humans actually multiple different species? Part of the confusion comes in the fact that the definition of species is something that isnt universally agreed upon, but my understanding and definition is when one animal branches out and gets isolated from the others and takes on some sort of mutation changing its physical features or colors while still being very similar to whatever it branched off from. Based on this definition I would have to say yes there are many different species of humans. I mean sure we all started in africa, but as humans moved out and were isolated from the rest of the populations we all changed. You will never find someone from africa that looks like someone from asia or america. Bone structure, skin tone, hair, and many other things are completely different and unique to each.

Is race just a nice way of saying species without stepping on people toes? I mean I can see how racist people could really take something like this and run with it but from a strictly scientific standpoint im quite interested in the answer.

I also realize that now humans have completely covered the earth so everything just gets blended to a million shades of gray, but I would still think this to be even more different species or subspecies even. So….what say you fluther?

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67 Answers

Simone_De_Beauvoir's avatar

I really really have to say no. Race is a social construct. All humans are virtually the same, genetically with slight variations due to demographics of their ancestry.

JilltheTooth's avatar

Species:
The major subdivision of a genus or subgenus, regarded as the basic category of biological classification, composed of related individuals that resemble one another, are able to breed among themselves, and produce fertile offspring, but are not able to breed with members of another species.

ninjacolin's avatar

All members of a species can mate and reproduce. That’s what makes them a species.

sometimes people use species as a misnomer when referring to dog breeds. Maybe you could say humans have different breeds but we’re definitely all one species.

ninjacolin's avatar

You might also find it interesting that there’s a biological event referred to as “speciation” where a mutation in the progeny of a population restricts the new borns from reproducing with the parent species. This is how a new species is born.

El_Cadejo's avatar

@ninjacolin so then youd say there are multiple breeds of human?

im also caught up on cases where scientists always thought two animals to be the same species but later find out due to some genetic difference theyre two different species. seems to happen a lot with fish

iamthemob's avatar

It really depends on what context you’re using the word “species” in – the various definitions can be found here. The definition is much, much more complicated than most, including me, realize.

Regardless, I don’t know if there’s really a useful reason to discuss whether racial differences should be attributed to “speciation.” It seems a more loaded issue that doesn’t necessarily provide us, nor seems capable of providing, significant scientific benefits…and will only end up confusing sociological, psychological, and anthropological discussions in my opinion.

@ninjacolin

Speciation in some contexts does not require, apparently, that the organisms be unable to mate – but that they have been reproductively isolated from each other. Therefore, the changes in morphology can be based on selection as opposed to mutation.

GeorgeGee's avatar

There is currently only one species, “Homo Sapiens Sapiens,” but there have been quite a few within the Homo genus, including Homo Neanderthalensis (Neanderthals) and Homo Erectus. More details:
http://en.wikipedia.org/wiki/Homo

marinelife's avatar

One species.

@ninjacolin hit it.

ninjacolin's avatar

Thanks, @iamthemob. Morphology it seems has been the most common way to tell species apart but I favor the reproductive ability distinction as a minimum requirement.

Rarebear's avatar

@GeorgeGee is absolutely correct. There have been multiple species and some recent evidence to show that H. Neanderthalensis and H. Sapiens may have interbred

Plucky's avatar

There is only one species of homo sapiens sapiens (the current human). If anything…race could be referred to as “breed” but nothing else :)

iamthemob's avatar

@ninjacolin as do I – and I think it’s the most common “layman” understanding of what speciation is and species are

GeorgeGee's avatar

Actually, the ability to mate and reproduce is common between many different species, for instance horses crossed with donkeys, but tends to produce sterile offspring, mules in this case. Lion-tiger “Ligers,” Coyote-dog “Coy-dogs,” and Polar Bear-Grizzly “Grolars” are among the commonly interbred animals.
http://www.scientificamerican.com/article.cfm?id=recipe-for-high-bpa-exposure
These aren’t merely the result of human tinkering either. Wild Grolars have been spotted and photographed:
http://www.mnn.com/lifestyle/pets-animals/stories/first-wild-polar-grizzly-bear-hybrid-offspring-discovered
and Coy-dogs are common.

Axemusica's avatar

I’m not a pure bred, I’m a mutt! I’m not disappointed at all. :D

ninjacolin's avatar

That’s cool, @GeorgeGee. Some more thoughts: When it comes to ability to mate and reproduce: If two “Breeds” are so different from eachother that they simply WON’T mate, and hence reproduce without human tinkering then they are effectively, if only through behavior alone, distinct species.

Also I would want know whether the child mixed-breed can successfully reproduce with both parent breeds. In the case of the gowlers, as long as the gowlers could still mate with both parent breeds, then I would say they’re all one species with different breeds just like dogs.

And again, we already know that visible morphologies were the archaic way of defining a species. It was the easiest way before science got better at it’s own game. I think it’s probably a good idea to improve on our definition.

CaptainHarley's avatar

If the offspring of any two creatures is able to mate and bear offpsring of its own, the original parents are the same species. Sometimes creatures can mate, but produce no viable offspring, such as a donkey and a horse… they can produce a mule, but the mule is always sterile; thus donkeys and horses are two different species.

Race is a convenient way for some people to categorize humans, and nothing more.

MissAnthrope's avatar

Humans are one species. If you compare DNA, you will find that genetic differences are really very minimal. Having different morphology doesn’t make a different species, nor does it even indicate a different ‘breed’ (I can give examples if necessary). It simply indicates different morphology. Humans are a pretty diverse species when it comes to that, but it makes sense because we’ve had to adapt to a wide range of environmental and cultural conditions.

GeorgeGee's avatar

Speaking of morphology, a very slight genetic mutation produces albinism, which occurs in every race and every species. The visible morphological changes are huge, but outside of coloring, really not much else is different. It’s a reminder that we can fairly easily be fooled by what we see or think we see.
http://www.francesfarmersrevenge.com/stuff/archive/oldnews2/albino/gallery.htm

CaptainHarley's avatar

Great answer, @GeorgeGee ! : )

Mikewlf337's avatar

There are diffent types of humans which we call races. Diffrent races same species.

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CaptainHarley's avatar

@Mikewlf337

Race is a myth perpetrated by lazy people who want bogus categories into which they can conveniently place other humans.

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Cirbryn's avatar

Currently there is only one species of human, but as recently as about 30,000 years ago (which is yesterday in geologic time) there were five: Homo sapiens, Homo neanderthalensis, Homo erectus, Homo floriensis and Homo denisova

@CaptainHarley wrote: “If the offspring of any two creatures is able to mate and bear offpsring of its own, the original parents are the same species.”

Response: Nope. The defining characteristics of a species are the evolution of reproductive isolating mechanisms that prevent significant gene flow. That doesn’t mean members of separate species can never produce fertile offspring, it just means they generally don’t. Lions and tigers can produce fertile offspring if coaxed into mating, but that doesn’t mean they’re the same species.

@CaptainHarley wrote: “Race is a myth perpetrated by lazy people who want bogus categories into which they can conveniently place other humans.”

Response: So do you feel there are no valid categories below the level of species for every lifeform, or are you just applying this to humans?

CaptainHarley's avatar

@Cirbryn I have neither the patience nor the inclination to argue the finer points of speciation with you, nor am I sufficiently conversant with the subject to do so, but, just by way of interest, Homo neaderthalensis was able to mate with Homo sapiens and it’s now estimated that a detectable amount of the DNA of almost everyone alive today is inherited from Homo neaderthalensis, which would make them the same species as us.

Rarebear's avatar

@CaptainHarley I don’t understand why you’re being argumentative. @Cirbryn is a biologist with a specialization in evolution and ecology and he’s teaching us something. I thought, like you, that speciation was where two species can’t produce offspring. I realize that I am wrong and I learned something.

Cirbryn's avatar

@CaptainHarley “Homo neaderthalensis was able to mate with Homo sapiens”

Yes I know. What I’m saying is that doesn’t make us the same species, any more than it makes lions and tigers the same species, or coyotes and wolves, or llamas and dromedaries.

iamthemob's avatar

@Rarebear

I’m with @CaptainHarley on this one a little bit – it’s the approach more than anything. The question to him reads very much like bait, even if not intended to. It was clear that the statement was commenting on the fact that when people try to place humans into species categories…there may be some ulterior motives and there will more than likely be some negative reactions.

The thing is, sometimes we’re talking about evolution, sometimes we’re not – even when evolution is a theme, sometimes its more of an analogy. I do the same thing sometimes when people use legal analogies – I start debating their perceptions of the law, and that’s not necessarily what we’re talking about.

ETpro's avatar

I was going to say that there used to be, but they held a big contest, and we won. But I see that @Cirbryn beat me to it and also explained it in far better terms. :-)

Even humans as different as 4’ 3” pygmies and 6’ 9” tall Maasai tribesmen are part of the same species, Homo Sapiens. Granted there are numerous deffinitions of the definition of the word, species, but none that are accepted broadly by science would find human racial differentiation to be a significant enough variation to qualify as speciation.

iamthemob's avatar

@ETpro

Why not? In the case of the Amazon and the Massai, there has been thousands, arguably tens of thousands of years of reproductive isolation. Perhaps multiple millions of generations.

If we’re working with a BSC concept, might that qualify?

Cirbryn's avatar

@iamthemob Well you certainly wouldn’t have “multiple millions of generations” of reproductive isolation. Just 2 million generations would be about 40 million years. Our ancestors of 40 million years ago were early monkeys.

The question of whether a Pygmy and a Massai could be different species is best resolved by looking for reproductive isolating mechanisms and also for intermediate populations with which each can interbreed and thus maintain genetic exchange. A reproductive isolating mechanism would be something like different mating seasons or cues. Inability to produce fertile offspring would of course count as well. Pygmies and Massai don’t have that. Put the two cultures within travel distance of each other and presumably you’d get some interbreeding.

iamthemob's avatar

@Cirbryn
CRAP! You’re right. I multiplied by a standard generation rather than divided. Damn….

mattbrowne's avatar

Not in 2010.

Mikewlf337's avatar

@CaptainHarley Race is not a myth. Different races have different features that are significantly different from the other races. I’m sure many people on here will label me a racist for my views but I am not.

Cirbryn's avatar

@Mikewlf337 You’re only a racist if you think you can judge the worth or mental characteristics of a person based on race. That said, for race to be a valid taxonomic group, each race would have to include the common ancestor of all its members. So African Blacks and Dravidian Indians and Australian Aboriginals can’t all be in the same “Black” race, since Dravidians descended from lighter skinned Indians and Aboriginals descended from East Asians.

mattbrowne's avatar

@Mikewlf337 – I disagree. Science revealed that there are no significantly different features. Take a group of 55 chimps and look at their genomes. There’s more diversity present in this group compared to all of the 7 billion people on our planet. Humans are almost identical genetically. Comparative genomics finally terminated the ill-conceived concept of race in the same manner as quantum mechanics terminated the concept of a deterministic universe.

Skin color or eye color or hair color isn’t what makes us human. It’s the structure of our brains, our sophisticated hands and our bipedalism.

Cirbryn's avatar

@mattbrowne
> Humans are almost identical genetically.

Not as identical as cheetahs. Yet cheetahs have at least 2 subspecies.

> Comparative genomics finally terminated the ill-conceived concept of race in the same manner as quantum mechanics terminated the concept of a deterministic universe.

Here’s a link to a genomic comparison of about 1,000 people from about 50 worldwide populations. (You have to download it): http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121.5610&rep=rep1&type=pdf

Check out page 1101: there are definite identifiable differences across populations.

Now what that paper is comparing are differences caused by genetic drift. You could theoretically find little or no such differences but still note morphological differences between populations that were caused by natural selection. And typically, morphological differences that are linked to particular geographic locales are what you need to identify sub-specific groups such as races or subspecies. So if this paper didn’t find clear differences that wouldn’t put the nail in the idea of races. But the fact that it did find clear differences does, I think, show that there’s been more than enough time and genetic variation for subspecific-type differences to develop.

And don’t count the deterministic universe out of the running either. :-) There’s a difference between not being able to find a determining variable and establishing that no such determining variable exists.

> Skin color or eye color or hair color isn’t what makes us human.

Sure, but they could be characteristics that help identify subspecific groups of humans, just as they help identify subspecific groups of birds and fish and other animals.

Mikewlf337's avatar

@mattbrowne you have a good point as well. Perhap ethnic group is more appropriate than race.

mattbrowne's avatar

Of course the genomes aren’t identical. Let’s carry out a simple test related to the three important human features mentioned above:

We’ll take 500 white and 500 black test subjects and carry out fMRI scans asking them to listen to some speeches, answer certain questions, let them look at pictures, ask them to describe objects, carry out some simple multiplications and so forth.

We also use 1000 X-rays of the test subjects hands (key feature) and pelvis/hip bones (bipedalism key feature).

Now like during a Turing test you have to decide black or white. Can anyone do this and find out about the race of the test subjects? Or the ethnic group (which is indeed a better term)?

El_Cadejo's avatar

@mattbrowne what about skull structure? A forensic scientist/anthropologist can look at a skull and easily tell if it came from a white male or african male

Cirbryn's avatar

@mattbrowne Why are you applying methods for identifying subspecific groups in humans that you wouldn’t use to identify such groups in any other species?

mattbrowne's avatar

@uberbatman – These minor differences in skull structures aren’t relevant when we try to define what makes us human. The Broca and Wernike areals in the brain are. The metacarpal bones of our hands and the relative length of their digits are. Language and tool-making capabilities are key.

Again, skin color or eye color or hair color or the shape of our lips or our noses isn’t what makes us human. It’s the (1) structure of our brains, our (2) sophisticated hands and our (3) bipedalism.

Therefore I was talking about a Turing-type tests for these main characteristics.

El_Cadejo's avatar

@mattbrowne but im not saying others arent human… im just saying different. There are different species of bear yet they all contain the main aspects of a bear, its the smaller differences that set them apart as a species

Cirbryn's avatar

@mattbrowne wrote: “Again, skin color or eye color or hair color or the shape of our lips or our noses isn’t what makes us human.”

Response: It’s not what makes a cheetah a cheetah either. But those things are still used to identify subspecific groups of cheetahs. So why are you trying to apply different methods for humans and other animals?

@uberbatman wrote: “its the smaller differences that set them apart as a species”

Response: Well in the case of different species, as opposed to different subspecies, it’s the reproductive isolating mechanisms that set them apart. There aren’t any populations of humans that are set apart from other human populations in that manner.

El_Cadejo's avatar

@Cirbryn but what about some of these different species that are, once introduced to eachother able to breed with one another?

Cirbryn's avatar

@uberbatman Generally the introducing involves situations where the reproductive isolating mechanisms are counteracted. For instance an isolating mechanism might be one frog species mates in the water and one mates on reeds or plants near the water. Introduce them in an area without such plants and the second species may make do. A common isolating mechanism is simple (but strong and universal) female preference for the markings or smells of members of her species. Introduce them such that her only mating option is a member of another species and she may take it, or alternatively may not be able to get away from the other-species male in confined quarters. Wolves typically keep coyotes out of their territories, but human hunting may disrupt pack structure so badly they can’t do that, and also leave individual wolves with no other mating options. One species may typically migrate at the time another species is undergoing its mating season, but if you keep them both together in an enclosed area such that migration isn’t an option, then they may mate.

El_Cadejo's avatar

@Cirbryn Right, I get that, but you were saying that different species can not mate. But then in that example you said they could and this was why. Now why wouldnt that same situation apply when humans less densely populated the earth? They were all isolated after all. Its only because how successful we were as humans that we all ended up coming into contact with all the other cultures. But if it were any other regular animal for those periods of times in isolation wouldnt you be able to call them different species?

Cirbryn's avatar

> Right, I get that, but you were saying that different species can not mate.

Hmm. Well if I said that I was wrong. Some different species can’t successfully interbreed at all, but that level of isolation isn’t required to define a species. You just need reproductive isolating mechanisms that prevent significant genetic exchange under normal circumstances in the wild.

> Now why wouldnt that same situation apply when humans less densely populated the earth? They were all isolated after all.

The idea is that the reproductive isolating mechanisms have to be genetically produced. They’re intrinsic to each species, not simply an accident of geographic separation.

El_Cadejo's avatar

@Cirbryn “The idea is that the reproductive isolating mechanisms have to be genetically produced. They’re intrinsic to each species, not simply an accident of geographic separation.” So are you saying this is something that can happen due to separation but didnt happen with humans or its something that just happens? I dont really follow because i mean there were quite a few animals that when Pangaea split they became isolated and were then two different species. Where humans not isolated long enough for that to happen or what?

Cirbryn's avatar

The development of reproductive isolating mechanisms requires at least two steps:

1) Incidental genetic isolation, which usually comes from geographic separation but could also come from other things as using a different mating ground or mating at a different time.

2) Differential evolutionary changes. So both populations have to start evolving in different directions, due to differing pressures from natural selection, sexual selection, or genetic drift.

3) If the populations have or regain the possibility of interbreeding again before the differential changes cause them to be too different to interbreed, then they may produce hybrids that are less able to survive or to reproduce with either parent population. If that happens, then any mutations that help prevent individuals from wasting their resources producing hybrids will tend to be naturally selected. So reproductive isolating mechanisms that prevent interbreeding will be selectively favored.

In humans there was some differential evolution, due to both selection and drift, but the populations re-established significant levels of interbreeding before Step 3 occurred.

El_Cadejo's avatar

@Cirbryn ahhh i see, thank you for clearing that up GA. Would you say there are different breeds of humans though?

Cirbryn's avatar

Well the term “breeds” usually refers to domestic animals. The technically correct term would be “subspecies”, which can refer to just about any amount of distinctiveness. For instance the Eagle Lake rainbow trout has two extra chromosomes compared to regular rainbow trout, along with other important physiological differences, whereas the Sacramento Valley tiger beetle (which just recently went extinct) was distinguished primarily by having swoosh marks on its shoulders that were a little swooshier than in other subspecies.

The problem is that most people hear the word “subspecies” and think of something that’s very distinct – almost a species in its own right. So that being the case, I think “race” is actually a pretty good term.

And I do think it’s reasonable to claim there are different races of humans, so long as we all understand that the term just refers to the existence of a few distinguishing characteristics of populations, and does not imply significant evolutionary separation or differences of worth or ability between members of any given races.

As to what those races would be, I think there are actually several reasonable ways to split them up, depending on what factors you focused on and whether you’re a lumper or a splitter. That’s not uncommon when identifying subspecies of other species either. The paper I linked earlier used seven groups, other papers I’ve seen have used five. You can’t really use the Black-White-Asian breakdown though unless you put the dark-skinned Dravidian Indians in with the Whites and the dark-skinned Australian Aboriginals in with the Asians.

My job involves listing species as endangered or threatened under the Endangered Species Act. The ESA defines “species” to include subspecies as well, so I tend to look at any purported subspecies from the point of view of asking whether it’s unique enough that we wouldn’t want to see it go extinct. When you look at it that way it’s pretty hard to say human races don’t exist.

Cirbryn's avatar

Some additional sources on this topic that are really good are:

Ernst Mayr on Race (Mayr was a developer and the best known supporter of the Biological Species Concept); and

Lewontin’s Fallacy (Lewontin claimed races don’t exist because there is much more genetic diversity within purported races than across them.)

mattbrowne's avatar

@Cirbryn – The question was not about identification of variations in the human species. There are thousands of even smaller variations compared to the skull shapes you mentioned. Comparative genomics can even reveal that the Viking males took plenty of English females with them when they began to settle on Iceland.

Another interesting research effort is about lactose tolerance:

http://en.wikipedia.org/wiki/Lactose_intolerance#Lactose_intolerance_by_group

http://en.wikipedia.org/wiki/Lactose_intolerance#History_of_genetic_prevalence

It’s one of the few human features with evolutionary change over a relatively short time span.

El_Cadejo's avatar

@Cirbryn ahh I see. thanks for clarifying that.

I love fluther for answers like the ones I’ve been getting in this thread…

Cirbryn's avatar

@mattbrowne > “The question was not about identification of variations in the human species.”

Well, the question was about whether there are multiple human species, and my position is that at the moment there’s only one human species, but there are human subspecies, which we call races. Subspecies are geographical populations that differ from each other morphologically.

If your point is that it’s a bit arbitrary what constitutes a “morphological difference” then to some extent I’d agree. But remember it needs to be linked to a particular geographic area. Lactose tolerance shows up independently in several geographic regions, and can be fairly variable even within such regions.

It’s also not something that would ever be likely to develop into a reproductive isolating mechanism, although that’s not strictly required of characteristics used to identify subspecies. But subspecies that eventually become species all pass through a stage where they have incipient isolating mechanisms that allow members of different subspecific groups to identify each other.

@uberbatman My pleasure.

mattbrowne's avatar

@Cirbryn – Well, let’s agree that we disagree. I reject both the notion of human subspecies and the term race. To me, all we got is ethnicity. And as of this moment 6,878,298,840 human genomes that are almost identical.

Cirbryn's avatar

@mattbrowne > “I reject both the notion of human subspecies and the term race.”

OK, but why just humans?

mattbrowne's avatar

Because of this

http://en.wikipedia.org/wiki/Subspecies

http://species.wikimedia.org/wiki/Homo

To my knowledge the subspecies homo sapiens sapiens and homo sapiens neanderthalensis are considered outdated.

So for the genus homo there are the following species:

H. sapiens – †H. antecessor – †H. cepranensis – †H. erectus – †H. ergaster – †H. floresiensis – †H. georgicus – †H. habilis – †H. heidelbergensis – †H. microcranous – †H. neanderthalensis – †H. orientalis – †H. platyops – †H. rhodesiensis – †H. rudolfensis

There is an extinct subspecies called †H. s. idaltu, but homo sapiens and homo sapiens sapiens are identical.

There are no homo sapiens white skin, homo sapiens black skin, homo sapiens skull shape 1, homo sapiens skull shape 2 and so forth.

Even the entry http://en.wikipedia.org/wiki/Caucasian_race reads

“the term Caucasian race has been used to denote the general physical type of some or all of the indigenous populations of Europe, North Africa, the Horn of Africa, West Asia, Central Asia, and South Asia.”

which doesn’t sound like a scientific definition, but popular use of a term.

Cirbryn's avatar

Alright, it sounds like you’re saying that human races don’t exist because none have been formally described. Do you have the same opinion regarding dog breeds?

mattbrowne's avatar

@Cirbryn – Yes, no dog subspecies. But dog breeds. Breed and subspecies are not exactly the same thing.

Cirbryn's avatar

Dog breeds are different in that they are no longer linked to a particular geographic area, because they can be bred by humans wherever the humans decide to do so. But they aren’t different from subspecies in terms of physical characteristics because the only formally recognized taxonomic rank below the level of species is subspecies. (See Article 45.5 here). As Mayr writes: “The terms “subspecies” and “geographic race” are used interchangeably in this taxonomic literature.”

So just because a group hasn’t been formally described, that doesn’t mean its physical differences from other groups aren’t legitimate. Such differences have to be judged on their own merits.

The reason human races haven’t been formally described is that the common interpretation of a subspecies is of a group having greater differences than human races have. But that’s an incorrect impression. There would also be the problem of what to call those individuals that don’t fall within a defined race. That generally isn’t worried about with other species, but would probably become an issue with humans because the term “hybrid” has negative connotations.

mattbrowne's avatar

@Cirbryn – I realize that there’s a gray area ;-)

amberrae's avatar

Two species… men and women…lol… very different creatures indeed!

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