Why is there only one human species?

[dipsydoodle]

Not so very long ago, we shared this planet with several other species of human, all of them clever, resourceful and excellent hunters, so why did only Homo sapiens survive?

Huge debates rage about human origins, but the broad consensus among scientists is that all the different species of human that have ever existed were descended from ape-like creatures that walked upright in Africa more than six million years ago.

These creatures had many descendants, most of which became extinct, but the first creature we would recognize as human first appeared in Africa two million years ago.

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Yet Homo erectus was slightly bigger and more powerful than Homo sapiens, so why did we thrive when they did not? The most obvious answer is that we had bigger brains - but it turns out that what matters is not overall brain size but the areas where the brain is larger.

http://www.bbc.co.uk/news/science-environment-13874671

For anyone who can get it :

Planet of the Apemen is on BBC1 at 2000BST on Thursdays from 23 June or catch up afterwards via iPlayer at the above link.

[LeftinOH]

1. There was another one until recently (geologially speaking): Neanderthals- but

knowing humanity, we probably wouldn't have gotten along very well.

[Somawas]

2. Neanderthals are alive and well

and vote Republican and listen to Fox and Rush.

[sarge43]

4. Nope.

There's evidence that the Neanderthals took care of their injured, sick and elderly. They were more evolved than Repugs.

[Orsino]

9. And Homo floresiensis hung on nearly into historical times. n/t

[n2doc]

3. Republicans are another species, IMO. n/t

[dipsydoodle]

10. Distiguishable in general by

their women having better legs. http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=439x1344809

[n2doc]

11. You tell me- Doesn't she seem like a different species?

[dipsydoodle]

12. Starey eyes

Spooky. :)

[nichomachus]

16. Never mind Tiffany's. They need a line of credit at the Botox salon.

[flying rabbit]

22. She is one of the Reptilians! nt

[xchrom]

5. recommend

[Uben]

6. Only one "known" species

.....to say there is only one species is hypothetical. Just because another species has not been yet identified doesn't mean they do not exist. I have strong doubts about whether Michelle BAchmann is human. I think she may be linked to the once thought extinct species Homo Ignoramus.

[dmallind]

7. Single species genera are not that rare. Now single species ORDERS....

...of those I can only recall one. I'm certainly no great biologist and quite possibly among the enormous diversity of beetles etc there sre plenty. But in the "animals-non-specialists-care-about-because-they-have-seen-pictures-or-zoo-exhibits-idae" category I think it's unique.

Anybody care to guess - it's an animal with which all are familiar? Not a platypus by the way....

[hunter]

13. (Spoiler!) Started thinking about freaky animals, guessed one, got curious, and found another...

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wikipedia

wikipedia

[dmallind]

14. beat me by one - could only think of your first example Cool. nt

[sharesunited]

8. Sasquatch strenuously objects.

[LaurenG]

15. When I was small I used to wonder that and why only male and female genders.

There are so many animal species ye we get stuck with only one and surely we could have a couple or three other genders to make it interesting. :shrug:

[mike_c]

18. a biologist's perspective is somewhat different....

Species are arbitrarily defined-- by biologists-- to make it easier to study biological diversity. There really isn't any such natural unit as a "species." It's a construct we use to organize biological diversity. It's better to think in terms of there being a wide range of genetic diversity and change through time-- mostly, it's biologists who sort and classify the outcome of those processes into "species," and even though the species is a fundamental unit in biology, we don't agree on how to define it, in fact, no definition of the term can be applied to all, or even a majority, of the "species" we recognize as distinct from other species. So questions like "how many species of human are there" are pretty meaningless from a biological perspective, even while they absorb lots of scientist's time and energy. That's one of the greatest paradoxes in biology, IMO, and an indication that our thinking is still too incomplete to comprehensively understand living organisms and their place in the universe. I personally tend to regard "life" as little more than complex chemical machines-- evolving, diversifying, and adapting to new environments through genetic and phenotypic variation along pathways that are likely fundamental to matter in our universe wherever conditions are amenable (a notion that promises some remarkable discoveries in "life-bearing conditions" that we recognize, but especially elsewhere where we might one day find other systems that exploit those same fundamental properties of matter in ways that are utterly alien to our thinking about "life" as we currently understand it-- can that level of complexity and diversity self assemble from non-organic organizing pathways, for example?).

The gender question seems to be a matter of parsimonious adaptation. Two genders is enough to fully exploit sexual genetic recombination, so there is little impetus toward more than two. On the other hand, if achieving reproductive fitness is the be all and end all of biological goals-- getting the maximum number of one's genes possible into viable members of future generations-- then ANY amount of sexual recombination represents a partial defeat. On average, sexually reproducing organisms in a two gender system achieve 50% transfer of their genes to their offspring, while asexually reproducing organisms can achieve 100% transfer. The benefits of sexual recombination are sufficient to make that 50% loss of genetic fidelity adaptive by exploiting genetic variation to solve adaptation problems and increase the chances of offspring surviving, but it's apparently not enough to support expansion into three or more genders, each of which would sacrifice even greater degrees of genetic inheritance in favor of increasing genetic recombination.

on edit-- remember too that "gender" is ultimately based on distinctions between gametes, not on distinctions between adults (except in so far as they produce different sorts of gametes). Thus "males" are the producers of microgametes (usually) while "females" produce megagametes. One can imagine a third way to have multiple genders that still only requires 50% loss of individual reproductive fitness when mating, e.g. three or more "genders", any two of which can partner to produce offspring would limit reproductive fitness loss to an average of 50% of genes no matter how many genders existed, but like "species," "gender" is a somewhat arbitrary notion that recognizes (easy to observe) phenotypic differences in place of (difficult to observe) gametic differences. At the gamete level, it's hard to imagine how some "third gender" might work. If sperm and ova are necessary for sexual recombination, what would a "third gender" produce other than sperm or ova, and wouldn't that make the third gender actually male or female no matter what their other differences?

Fascinating questions, aren't they?

[gtar100]

20. Awesome post. Thanks!

[nichomachus]

17. The other species

took one look at us and got the hell out.

[Odin2005]

19. We killed the others, just like we killed all the megafauna.

[sofa king]

21. Ruthlessness, collective warfare, assimilation.

I think just those three things could have spelled the difference, though there's no way for me to currently guess whether any of those are the things which actually played a role.

But humans definitely fight in a way that's different from other primates. We are able to perceive the things that are essential to the functioning of a healthy society, and during wartime (and other times), we focus our attacks on those things, apparently out of instinct or some deep-seated need to destroy even at our own expense.

Thus, we crap in springs and creeks, kill all the men and carry away the women, pull down or burn structures that could be of later use to us, disrupt the local economy through looting, chop down the trees, and so on. We are all Vandals.

If, for example, the Neandertals were more individualistic, maybe even smarter, they might have had central locations which they did not protect as well, even though they did not range as far from them. Humans would naturally attempt to evade the formidable warriors and go straight for the women and loot in the camp.