Until quite recently conventional scientists were adamant that there was no hybridization between H. sapiens and H. neanderthalis. Then, Svante Paabo upset that apple cart with the Neanderthal Genome Project concluding that people with ancestry outside of Africa share 1% to 5% of their genome with Neanderthals.
Now, the plot thickens as genetic studies begin to show that breeding with brutes had its benefits, especially when it came to disease resistance:
http://www.newscientist.com/article/mg2 ... nline-news
Denisovans are also mentioned in the above article. The trek out of Africa must have been one big love fest.
