Sex with Other Human Species Might Have Been Secret of Homo Sapiens’s Success

[n2doc]

By Michael F. Hammer

It is hard to imagine today, but for most of humankind's evolutionary history, multiple humanlike species shared the earth. As recently as 40,000 years ago, Homo sapiens lived alongside several kindred forms, including the Neandertals and tiny Homo floresiensis. For decades scientists have debated exactly how H. sapiens originated and came to be the last human species standing. Thanks in large part to genetic studies in the 1980s, one theory emerged as the clear front-runner. In this view, anatomically modern humans arose in Africa and spread out across the rest of the Old World, completely replacing the existing archaic groups. Exactly how this novel form became the last human species on the earth is mysterious. Perhaps the invaders killed off the natives they encountered, or outcompeted the strangers on their own turf, or simply reproduced at a higher rate. However it happened, the newcomers seemed to have eliminated their competitors without interbreeding with them.

This recent African Replacement model, as it is known, has essentially served as the modern human origins paradigm for the past 25 years. Yet mounting evidence indicates that it is wrong. Recent advances in DNA-sequencing technology have enabled researchers to dramatically scale up data collection from living people as well as from extinct species. Analyses of these data with increasingly sophisticated computational tools indicate that the story of our family history is not as simple as most experts thought. It turns out that people today carry DNA inherited from Neandertals and other archaic humans, revealing that early H. sapiens mated with these other species and produced fertile offspring who were able to hand this genetic legacy down through thousands of generations. In addition to upsetting the conventional wisdom about our origins, the discoveries are driving new inquiries into how extensive the interbreeding was, which geographical areas it occurred in and whether modern humans show signs of benefiting from any of the genetic contributions from our prehistoric cousins.

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http://www.scientificamerican.com/article.cfm?id=sex-with-other-human-species-might-have-been-secret-homo-sapiens

[undeterred]

1. How is a "species" defined?

I thought it had to do with the inability to interbreed.

[Lawlbringer]

2. you can cross breed

amongst species and even genus if in the same family, but while the former works out well, the latter generally does not.

[stopwastingmymoney]

3. What I remember from Anthro class

Was the ability to breed and produce fertile offspring.

[Enrique]

4. that was my question

would this mean Neanderthals would no longer be considered a separate species?

[Geoff R. Casavant]

5. That's the general definition, but there are always exceptions.

Life is in such a broad and fine spectrum that when certain species are closely enough related, the distinctions can become blurred.

There are certain "ring species" such as a salamander in California, which live in an incomplete ring around the San Joaquin Valley. Each subgroup in the ring can easily interbreed with the subgroups on either side of it, which would lead one to believe they are the same species. But the subgroups at the ends, for example, are so different they cannot interbreed and so are truly distinct species.

[Yo_Mama]

6. No

For example, polar bears can interbreed with other bear species.

The "species problem" debate has gone on for a long time, and the ability to analyze DNA has actually changed species designations:
http://en.wikipedia.org/wiki/Species_problem

The commonality among species definitions would be reproductive isolation and different characteristics, but the reproductive isolation doesn't have to be biological. It could be mostly geographic or adaptive.

The combination of locally adapted traits and some degree of reproductive isolation is what maintains separate species even if they can interbreed. Take polar bears. They are known to successfully interbreed with brown bears and grizzlies. However, the adaptations that the polar bears have to their environment maintain the advantage that their genome has against brown bears and grizzlies in their range, so the species remain separate.

http://e360.yale.edu/digest/unusual_number_of_grizzly_and__hybrid_bears_spotted_in_high_arctic/3567/

[Scootaloo]

7. It's really not

"Species" is essentially just a sorting tool to make the lives of taxonomists a little easier. There are no actual walls that define "species" in nature.

Many "species" are totally interfertile with one another (the Canis genus comes to mind) and are separated only by geography. Some others are separated by behavior... which can become interesting when you find out you have two identical organisms that behave differently and thus tend to not breed together (some species of frogs, for instance are the same all over, but have different ribbets... mostly). And then there's that whole "ring species" phenomena, which illustrates that there is no "break" in evolution where one species clearly stops and another clearly begins.

Species is a wibbly-wobbly descriptor that is vaguely based off Platonic idealism and partly off pre-molecular biology and mostly off taxonomists not wanting to have to deal with three or four extra categories after Genus

[pscot]

8. Illuminating post .

Thanks.

[Orsino]

9. It would have made a great pick-up line, anyway. n/t

[formercia]

10. When you're drunk, they all look good.

[Fumesucker]

11. There's even a word for it already

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