But did humans and Neanderthals have “heat” cycles? Humans can mate at any time of the cycle, up to and including shortly after delivery.
I’ve always blamed the long, flat, bumpy skull, prominent orbital ridges and extremely deepest eyes I inherited from my dad (along with blue eyes, reddish blondish hair, and fair super-sensitive skin) on Neanderthal genetics. Funny to see it might not be entirely a joke.
Not as such. However, nursing an infant depresses fertility in humans. Killing any breast-feeding infants will increase the probability that the female will conceive sooner. In any case, unrelated dependent children are a burden without a genetic benefit to a male, and so any small children might be killed.
That, and most parents of small children can tell you just how much opportunity and desire Mom has for sexy time when she’s been pawed at all day and night…I can’t imagine that that was any better for more primitive humans.
Re: breastfeeding and fertility, the stimulation of oxytocin in a nursing female also depresses desire (biologically, at least). To the body, it’s as though you’ve already done the deed that day.
Depends on what you mean by “heat” cycles and “mate”. We know that female chimps advertise their estrus cycle prominently and the males find it irresistible-- something that modern humans do not do (or at least do not do is such an obvious way). It’s unlikely that Neanderthals were more like chimps, but we really have no way of knowing.
OTOH, bonobos, at least, seem to be more than willing to “mate” approximately every 15 minutes. 
I put mate in “” because a lot what they do is genital rubbing (no penetration) and a lot of it is done between same sex partners.
Are the percentage calculations even looking at the same thing? Looking at percentages by base-pairs and by genes will give very different numbers.
Given ten genes, each with 10 base-pairs, and one base-pair difference total, the comparison of base-pairs would say 1% difference, but the comparison of genes would say 10% different.
Now that we know the non-coding dna really is actually coding for stuff - seems like any calcs about % similar can’t be just gene based, although that might give a substantially close number.
How common is/was this in primitive human groups?
I’m not advocating for the model suggested in TruCelt’s post, that is of males taking over a group and killing existing infants to bring females into reproductive condition more rapidly. I was just commenting on what happens in other mammals.
Based on recent primitive societies, I think it would be far more likely that Neanderthal genes might have gotten into sapiens through the occasional adoption of young captive or orphaned Neanderthal females into sapiens bands, than by male sapiens taking over a Neanderthal band in order to breed with females by killing the males and infants. As I said above, in some primitive societies it was common to take captive females or children from raids into the band.
There are many different ways of calculating % differences between DNA samples, and they’re all measuring very different things. These numbers are pretty meaningless unless you examine exactly how they were calculated, which is usually buried somewhere in the Materials and Methods section, if you’re lucky and they didn’t just reference another paper, which referenced another earlier paper, and so on.
Neither am I really. If I had to state a preference it would be for the attraction/protection model. My point is just really that I don’t see the need or any substantiation for the “mule” model.
Actually, there is more specific genetic evidence from the Nature study:
This is consistent with a principle of genetics known asHaldane’s Rule;
In humans and other mammals, males (XY) are the heterogametic sex.
Previously it was thought that because there is no trace of Neanderthal mitochondrial DNA (which is inherited purely through the female line) in modern humans, this indicated that most hybridization would have been by Neanderthal males crossing with sapiens females. However, Neanderthal mtDNA lineages could have died out purely by chance.