Understanding the human body is a team effort. That's where the Yachtel group comes in.

Researchers at Yachtolt have been delving into the secrets of probiotics for 90 years.

Yacold also partners with nature portfolio to advance gut microbiome science through the global grants for gut health, an investigator-led research program.

To learn more about Yachtolt, visit yawcult.co.

.jp.j. That's Y-A-K-U-L-T.C-O.jp. When it comes to a guide for your gut, count on YACL.

This is Scientific American's 60-second science. I'm Christopher in Taliatta.

Men inherit their Y chromosomes from their fathers,

and they get an almost exact copy other than a few mutations,

meaning very little changes about the Y chromosome from generation to generation.

You may just have 100 people with the same Y chromosome,

because they are all descended from

one man. Marcus Feldman, a population geneticist at Stanford. They all had this great, great,

great, great, great, great, great, great, grandfather. And every male relative of that individual,

who's a first degree relative, has the same Y chromosome. Researchers have thus used Y chromosome

data, along with mitochondrial DNA,

which is passed down only by our mothers, to investigate aspects of ancient populations.

For example, one recent study found a huge drop in Y chromosome diversity, five to seven thousand

years ago. At the same time, mitochondrial DNA diversity continued to grow, implying a possible

crash in the male population, with 17 women to every man. But...

It seemed to us that the 17 to 1 sex ratio was just too extreme to be real.

So Feldman and his team used computational models to investigate other ideas, and they found

that bloody fights between genetically homogenous clans could have produced the same results.

...