The U.N.'s current projection is that humanity will number 9.3 billion individuals in 2050 and then hit 10.1 billion by 2100. Meanwhile, our energy resources are dwindling, and droughts threaten our food supplies.

Humans have continued to evolve quite a lot over the past ten thousand years, and certainly over 100 thousand. Sure, our biology affects our behavior. But it's unlikely that humans' early evolution is deeply relevant to contemporary psychological questions about dating or the willpower to complete a dissertation.

As fears about the energy and environmental crises reach a fever pitch, we're all searching for solutions. And one possibility is that we could fix everything if we'd just shrink our population back down to about 2 billion people - which would put us roughly where we were at 80 years ago.

The U.N.'s current projection is that humanity will number 9.3 billion individuals in 2050 and then hit 10.1 billion by 2100. Meanwhile, our energy resources are dwindling, and droughts threaten our food supplies.

Millions of nerdy kids who grew up in the 1980s could only find the components they needed at local Radio Shacks, and the stores were like a lifeline to a better world where everybody understood computers.

There can be problems with extended families, and it can get a little close for comfort. But for the younger generations, it's clear that this option is becoming almost as appealing as living alone.