There are many species on Earth whose lifespans extend only long enough for each individual to do their part in propagation. Why, then, have humans developed over the years to live well beyond our reproductive years? According to Bill Nye, our ever-expanding longevity can be attributed to the remarkable usefulness of tribal elders: patriarchs, matriarchs, grandparents, and mentors. We’ve evolved to live beyond our reproductive years because, as the saying goes, it takes a village.

Julie: Hi Bill. My name is Julie and I’m in my 50s so my reproductive years are behind me. Yet I expect to live for about 40 more years. So my question is why? What is the evolutionary advantage to living way beyond the years it takes to see your children born and raised? How has that been selected for and why does that happen? Thanks.

Bill Nye: So Julie, I’m sure you’ve heard this many times. Julie, Julie, Julie. No you have great value to the tribe as an elder. Every tribe, every human tribe around the world has elders. They look to elders for guidance, for experience. Furthermore what is every bumper sticker in certain neighborhoods about? Grandchildren. Grandkids love grandparents. Grandparents have a great role and how many times have you, Julie — I don’t know you — heard your mother’s words coming out of your mouth? It’s frustrating, I know. But you’ve heard it. It’s like, "I can’t stop it; my mother is speaking through me." I know. So you have great worth as an elder in the tribe. Don’t set that aside. And furthermore, I’m delighted that you expect to live 40 more years but until recently nobody lived all that long. So I mean not to be dismissive of 50, way to go. I’ve been there for years. But to get into the 90s is — a lot of people are doing it now, but they didn’t used to. So enjoy it. Carry on. Offer your advice.

Furthermore now I don’t know if this is people working backwards to get the answer they expected or if they really made the discovery here, but there’s a very reasonable claim that our brains change as we get older and we are not as excitable. We don’t fly off the handle as readily and this is the word that you would use in English is your judgment becomes tempered or managed or evened out. When you temper steel, you give it certain properties. As you get older, your brain develops certain properties. As you get older your brain develops certain properties. So Julie, carry on as a tribal elder. I mean I discourage you from going up to everyone you meet and just start giving them advice; you might have trouble with that. But I’m sure you’re a force in your family and if you have grandkids, I can guarantee you’ll be a force in their lives. So carry on Julie. That’s a great question.