Visitors at the Museum for Prehistory in Eyzies-de-Tayac look at a Neanderthal man ancestor's reconstruction.
Just by looking at fossilized fingers, a group of British scientists say Neanderthals were, well, promiscuous ancesters.
In the paper, released in the scientific journal Proceedings of the Royal Society B, scientists argue that the relative size of fingers can tell us a lot about sexual activity. I'll let Rosemary Joyce over at Psychology Today's What Makes Us Human do the explaining:
When infants in the womb are exposed to high levels of androgens — steroid hormones that contribute to formation of male sexual anatomy — the lengths of fingers are affected, so that finger length ratio is a proposed ("putative") sign of this exposure.
Since we have no access to actual measures of androgen levels in the bodies of ancient human ancestors (let alone to their fetal levels), the durable finger bones provide an indirect (hence "putative") measure of relative levels of androgen exposure.
In studies of living monkeys and apes (haplorrhines), the ratio of forefinger (2D) to ring finger (4D) is correlated with forms of sexual pairing: species that form durable bonds between a single male and female have higher 2nd to 4th digit ratios as a result of having lower exposure to androgens in the uterus. The reverse is true of species where males mate with multiple females: they have lower 2nd to 4th digit ratios, indicating they were exposed to higher androgen levels.
BBC Mundo adds that when the scientists compared Neanderthal fingers to human fingers, they found that that 2nd-to-4th digit ratio was lower in our ancestors than in most modern-day humans.
Anthropologist John Hawks throws some cold water on the whole thing, though, reminding us this is simply a correlation not a cause.