Along our evolutionary journey from monkey-like primates to bipedal apes to big-brained humans, we have had the company of an extraordinarily loyal companion: Pediculus humanus, otherwise known as the human louse.

And all the while, the lice have recorded this journey in their genes. A new study, for example, found that some lice in the Americas are hybrids of those carried there by Native Americans and others ferried across the Atlantic by European colonists.

Continue reading “Lice Genes Offer Clues to Ancient Human History” →

For biologists, menopause is baffling. If natural selection favors genes that produce more descendants, why don’t women remain fertile their entire lives? What’s the evolutionary benefit of living for so many years without having more babies?

The mystery has only deepened as scientists have looked for menopause in mammals in the wild and found clear evidence of it only in a few species of whales. “It is very, very rare,” said Kevin Langergraber, a primatologist at Arizona State University.

Continue reading “Chimpanzees Go Through Menopause, Too” →

An international team of scientists has mapped the human brain in much finer resolution than ever before. The brain atlas, a $375 million effort started in 2017, has identified more than 3,300 types of brain cells, an order of magnitude more than was previously reported. The researchers have only a dim notion of what the newly discovered cells do.

The results were described in 21 papers published on Thursday in Science and several other journals.

Ed Lein, a neuroscientist at the Allen Institute for Brain Science in Seattle who led five of the studies, said that the findings were made possible by new technologies that allowed the researchers to probe millions of human brain cells collected from biopsied tissue or cadavers.

In more than 1,500 animal species, from crickets and sea urchins to bottlenose dolphins and bonobos, scientists have observed sexual encounters between members of the same sex.

Some researchers have proposed that this behavior has existed since the dawn of the animal kingdom. But the authors of a new study of thousands of mammalian species paint a different picture, arguing that same-sex sexual behavior evolved when mammals started living in social groups. Although the behavior does not produce offspring to carry on the animals’ genes, it could offer other evolutionary advantages, such as smoothing over conflicts, the researchers proposed.

In the 1970s, soft-shell clams started mysteriously dying off in Maine and the Chesapeake Bay. Years later, scientists identified the culprit: a bizarre form of cancer that spread like an epidemic.

When people get cancer, it typically arises when some of their own cells gain mutations and multiply out of control. But the clams were being invaded by free-floating cells that came from other clams. The alien cancer cell multiplied inside its new victim, and then some of its descendant cells escaped to attack other clams.

Continue reading “Bizarre Cancer Has Been Spreading Among Shellfish for Centuries, Studies Find” →