Menopause is a puzzle for biologists. Why would the female of a species cease to reproduce half way through her life, when natural selection favors characteristics that help an individual's genes survive? A study of killer whales — one of only two mammals apart from humans to undergo menopause — is providing clues.
When you think of sand, you might think of something brown, or white, if you're lucky. Maybe black if you're on a beach on Hawaii's Big Island. But the reality is sand is a melange of colors as varied as the rainbow.
As summer ends, people are cramming in that much-needed vacation in increasing numbers. But not everyone is taking them, indeed a quarter of American workers get no paid time off. And that's a problem for our brains.
No one quite knows when humanity's direct ancestors — the Homo genus — first evolved, but a fossil discovered in Ethiopia in 2013 may provide clues. And according to new studies, those clues point back further into time than was previously thought.