The Green Beard Hypothesis

If you read books, watch television or go to movies, you know that every story has to have a hero. And maybe you’ve noticed how many of those heroes die young. As you furtively dabbed the tears from the corners of your eyes, perhaps you’ve wondered:

If an attribute such as heroism, by definition, puts heroes at risk of losing more than they gain then why would such a characteristic be carried down in the population?

Shouldn’t heroic genes be buried with heroes? Shouldn’t heroes die out burned at stakes or crucified on crosses, leaving us mercenary types to carry on the species, bequeathing our selfish genes on down through the generations?

Science can be so cold-blooded when it comes to the sublime.

But wait! Actually an evolutionary rationale for the survival of heroic genes has been described mathematically in this way:

The ratio of benefit for the recipient of a heroic act, to the cost for the hero, must be greater than the reciprocal of the coefficient of relationship.

i.e., k>l/r, where k = ratio of benefit to cost, and r = coefficient of relationship.

(The coefficient of relationship is the probability that two persons have in common a gene that came from the same ancestor.)

What does this mean?

If I share 50% of my genes with my son, 25% with my niece, and 12.5% of my genes with my first cousin, and I lose my life in an act of heroism, I would have to save e.g. at least one son and one niece or nephew plus two first cousins to preserve 100% of my genes in the population.

A shabby bit of rhetoric? Wait. It gets worse.

Imagine that I had a green beard and my wife, enamored with that attribute, married me for that green beard (and those were inheritable attributes). Then our children may be endowed with genes for green beards but also with genes for a preference for men with green beards.

How does this help our hero?

If three of my children (each containing 50% of my genes) are caught in a fire and I can save one child at the loss of my own life, then half of my genes would be carried on into the propagation market. If I saved two, then of course double that percent survive; but if I can save three, even at the loss of my own life, then 150% of my genes would be carried on with the potential for reproduction—the ultimate imperative for a gene.

And should my wife have selected me for that altruistic characteristic then our children might have two inheritable characteristics: one for heroism and the other for preference of heroism, my wife’s attribute.

Quite a profit!

My children then might tend to be heroic and also might tend to be attracted to heroism as a characteristic in a mate.

But “Aha!” you say. ‘What if, on the other hand, your wife was attracted to ruthless selfishness and you were an extremely ruthless and selfish (non-heroic) individual? Your children would then be predisposed to ruthless self interest and have a tendency to be attracted to that characteristic!”

But that way—without the gene for heroism—when that fire starts, there’s no way that I’ll jump in after the kids! The result, a conflagration of genetic selfishness.

So nature demands our concern for each other, rewarding altruism geometrically for mothers and sons, nieces and nephews, all the way down through 52nd cousins.

Down the slide of diminishing relationship goes diminishing concern and altruism.
But the blood of green-bearded heroes flows in all of us.