Sibling Deidentification

I didn't know it either: It's a fancy term for not doing the same stuff that your brothers and sisters do:

The idea is that siblings need to avoid competition.  Sibling competition is nothing to take lightly.  Sibling colonies of bacteria secrete antibiotics that kill each other off.  The first African black eaglet out to hatch of its egg pecks the second one to death.  A quarter of spotted hyena pups are killed by their siblings.  The siblings are competing for their parents’ resources and attention, of which the parents have only a certain amount.  So the siblings are operating in a closed system...

But Cain and Abel aside, we humans can’t go killing off our siblings, so we agree to go our separate ways, we deidentify, we stake out separate niches.  To be honest, I don’t see how that makes the pie bigger or the parents have more resources; it just keeps us off each others’ backs...

And here’s the charm of it: a closed system might be lethal for competitors but it’s golden for cooperators. If my brother and I are one system and he knows statistics, I don’t need to; any statistic that needs to be done, he does. ... Closed-system cooperation is a great labor-saving device.

It's an interesting explanation for the differences between people that usually have essentially the same initial upbringing. I see this personally: my brother and I are very similar at our core, but have very different personalities and interests. Ann Finkbeiner goes on to say that the theory extends to spouses as well, which means that it's something that's learned, not hereditary. Fascinating. I'll have to ponder this more.