In order not to quote a short text in the whole, let me just summarise it a bit and say that, according to research conducted by Doctor Lahn from University of Chicago, modern humans have likely interbred with the more archaic species, such as Neanderthals (note: Neanderthals were sapiens also). Such interbreeding is thought to have been rare, if not a single occurence, as it seems that an allele present in 70% percent of modern humans comes from a single source situated 37000 years ago.

Here (http://www.pnas.org/cgi/content/abstract/0606966103v1) is the article.

This was something that was hypothesized over 20 years ago. The anthropological trend was that homo sapiens combined with homo sapiens neanderthalesis to make the true homo sapiens sapiens (humans today).

It's interesting that genetic technology is capable of validating that theory.

It is more than likely that in areas that were inhabited by neanderthals that they were partially absorbed into cro-magnon populations that were moving in to europe and the middle east, as there are numerous locations where it is seen that anatomically modern humans and neanderthals co-existed for thousands of years. There are also finds of individuals from known locations of co-habitation exhibiting a combination of neanderthal and cro-magnon features. This is not really suprising since the neanderthal population seperated from the main human lineage, and the same has happened with wolves and domestic dogs. They are clearly seperate species with differing, albeit similar, behaviour patterns, yet they can readily interbreed. However, if the gap between two off-shoots of the same lineage is too great, interbreeding cannot happen. Such can be seen with domestic cats being unable to breed with cheetah, with both species having a common ancestor - one that differed from the common ancestor of the panthera species.

I read once that a possible genetic carry over from neanderthal and cro-magnon inbreeding is the gene for red hair...

This is not really suprising since the neanderthal population seperated from the main human lineage, and the same has happened with wolves and domestic dogs. They are clearly seperate species with differing, albeit similar, behaviour patterns, yet they can readily interbreed.Um - you realise that the definition of 'separate species' is that they can't produce fertile offspring, right? If they can do that than they are clearly not separate species.

Donkey and horse are seperate species, and from time to time they produce fertile offspring. Lion and tiger are seperate species, and from time to time they produce fertile offspring.

Donkey and horse are seperate species, and from time to time they produce fertile offspring. Lion and tiger are seperate species, and from time to time they produce fertile offspring. AFAIK, the offsprings of horses and donkeys, in other words "mules", are not fertile, they can't reproduce. But I don't know if there are any exceptions.

http://en.wikipedia.org/wiki/Mule#Fertile_mules

If it can happen with mules and hinnies then it could have happened with humans and neanderthals etc.

Also just found a hybrid of sheep and goat, two seperate families of animal that are unrelated.

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

[ November 11, 2006, 15:00: Message edited by: Nataraja ]

Um - you realise that the definition of 'separate species' is that they can't produce fertile offspring, right? If they can do that than they are clearly not separate species. No. Some species can cross-breed and produce fertile hybrids, for example: D. silvestris and D. heteroneura.

When two seperate species cross I think its called a chimera.

A chimera (generally) refers to an organism which contains genetically different cell populations, derived from different zygotes.

@ Aik
The definition of a species (unlike what we were taught at school) is pretty loose. There are no definite boundaries.

Chimeras have more than one DNA. Some of their tissues have one DNA and the others have another DNA. It is like two creatures in one body. Its main reason is the uniting of two different zygotes in uterus somehow in the early days of pregnancy, IIRC.