YAEDA VALLEY IN TANZANIA—As we hike down a rocky slope, through thorny acacias that snag our clothes and past the emaciated carcass of a cow, we hear people singing. We are approaching a small camp of Hadza hunter-gatherers, and our Tanzanian guide thinks they must be celebrating something.

There are two kinds of sleepers in this world. Night owls who have energy well into the evening and go to bed late. And early birds, the ones who subscribe to the early-to-bed-early-to-rise regimen. You probably have a good idea of which category you fall into most of the time, but you might not know why or how to switch over into the other camp. Or even if you should.

It may not seem obvious at first, but the pollination prowess of bees affects much of what, how and why we eat. And it goes far beyond honey served from a jar.

We have a strange nostalgia for our hunter-gatherer days. Despite the fact that many of our ancestors died grim deaths at the hands of animal teeth and simple infections, we seem to cling to the idea that humans were somehow healthier and just, well, better when living off the land. It’s for this reason that many turn to diets based on what either ancestral humans or modern-day hunter-gatherers would eat.

Human behavioral ecologist Alyssa Crittenden of the University of Nevada in Las Vegas has studied the Hadza since 2004.

What does research suggesting we should focus on diet, not exercise to lose weight and the evolutionary reason we sleep less as we age have in common?

Much like the weather, some human stomachs change throughout the year. The gut microbes of the Hadza, a hunter-gatherer group in Tanzania, shift dramatically as their diet changes with the seasons, according to new research from Stanford University. When applied on a longer timescale, these trends could explain why industrialized populations have a less diverse set of gut microbes and more chronic disease relative to hunter-gatherer populations.

A sound night’s sleep grows more elusive as people get older, but what some call insomnia may actually be an age-old survival mechanism.