One of the biggest surprises about our evolution revealed over just the last decade is the extent to which our ancestors engaged in amorous congress with the evolutionary cousins.
Bonking the Neanderthals, it seems, was a bit of a pastime for the distant relatives. It happened many times in Siberia, East Asia, the Middle East and Europe, and across a long period between 100,000 and 40,000 years ago.
In reality, we have no idea of course exactly how many times it occurred, nor the circumstances in which it happened. Who instigated it, us or them? Was it consensual? Did they pair for life? Or was it a casual fling?
Now, the consequences of interbreeding for us today are becoming all too clear from studies of the genome - theirs and ours - ancient and modern.
Somewhere between 1.5% and 2.1% of your genome was inherited from the Neanderthals, assuming your ancestry was non-African of course.
East Asians typically have more Neanderthal DNA because their ancestors partook in a little more afternoon delight than the rest of ours did.
For Indigenous people living around eastern Indonesia, and in New Guinea and Australia, their ancestors also took a shine to the ‘Denisovans’. In their genomes we find n extra 4% to 6% inherited from this mysterious species.
So far, archaeologists have found just two finger bones and a tooth from the Denisovans, thousands of kilometres away from New Guinea in southern Siberia, of all places.
Yet, the fact that the earliest New Guineans mated with the Denisovans only 44,000 years ago - as revealed by their DNA - suggests that all the action happened in the tropical climes of Oceania, not icy Siberia.
Don’t fret if your ancestry is African though, your ancestors found another human species or two to bonk.
Surprisingly, the genomes of the West African Biaka and Baka (so-called ‘pygmy’) people have revealed DNA from a completely unknown species, which found its way into the human genome only 9,000 years ago.
Other studies have found much wider evidence for interbreeding across Africa, occurring sometime around 35,000 years ago.
It’s fun to think about our surprisingly mixed-up heritage as a species. And may be even poke fun at a friend or two for their seemingly excessive amounts of Neanderthal DNA.
But there’s a serious side to all of this as well. The legacy of interbreeding is very real and seems to explain quite a few modern ailments, and some rather nasty diseases as well.
Neanderthal DNA is associated with an increased risk of developing skin corns and callosities, mood disorders and depression, overweight and obesity, upper respiratory and urinary tract infections, incontinence, hardening of the arteries and even smoking.
Then there’s those immediate risks that come with casual sex with your own, or in this case, another species.
Like catching a parasite such as body lice, or worse still, contracting a sexually transmitted infection.
Body lice are parasites that evolve in tandem with their hosts. Other mammals have them, but human lice species are unique to us, and spread through close contact such a sex.
A person can be infested with thousands of these blood suckers, each insect biting five times a day.
But worse, they also carry deadly bacteria. Diseases like endemic typhus are carried and spread by body lice and are said to have caused more deaths than all the wars in history put together.