This is scientific American's 60 second science. I'm Christopher Intalyata. Got a minute?

Homosapians may dominate Europe and Asia today, but hundreds of thousands of years ago, long before we got there, the land was ruled

by our now extinct cousins, the Neanderthals and Denisovans.

I think one important thing to realize is that given that

the Neanderthals and Denisovans had lived in Europe and Asia for such an extended time,

they were probably quite well adapted to the local conditions.

Janet Kelso, a computational biologist at the Max Planck Institute for Revolutionary anthropology.

So they were well adapted to the pathogens, to the foods that were available to the climate.

The invading newcomers probably found themselves less well adapted to the local conditions.

So when Homo sapiens shacked up with their close evolutionary relatives,

it gave them a shot at picking up some advantageous genes.

Kelso and her colleagues hunted modern human genomes for strings of DNA that closely

resembled those known to be from Neanderthals and Denisovans.

And indeed, on human chromosome number four, they found a stretch of archaic DNA, 140,000

bases long.

The genomes of many non-African humans today have this sequence, which includes a cluster of genes that code for toll-like receptors or TLRs, a type of immune protein that sniffs out pathogens.

And it turns out that archaic variants of that gene

are associated with lower microbial loads in present-day humans,

a trait that may have been quite valuable to our ancestors as they settled new lands.

The study appears in the American Journal of Human Genetics.

Problem is that increased immune vigilance, it has a side effect, allergies.

A speculation is this is some kind of trade-off, right?

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