Bryan Caplan  

Evolutionary Psych and the Generation Gap

PRINT
Is Health Care Worth It, Con't... Freak Storm...

Watching War of the Worlds reminded me of one of the big puzzles in evolutionary psychology: Why do parents and their children disagree? "I only want what's best for you" is every parent's slogan, and if Darwin is right, how can that be wrong? It's one thing to say that evolution isn't perfect. But in the real world, we often see a son defy his parents to join the guerillas, or a daughter elope with a poor but dashing suitor. Not to mention the mundane struggle to make kids do their homework.

This is one of those questions where I humbly (?) suggest that a little economics goes a long way. Suppose a headstrong daughter defies her parents to marry beneath her station. (Forgive my archaic language, I'm re-reading War and Peace.) Is she the only person whose genes are affected by this decision? Hardly. There is an obvious negative externality for her siblings, who will see their opportunities in the marriage market diminish. And since your parents are equally related to all their children, but you are only half as related to your siblings as you are to yourself, the selfishly optimal choice for your genes differs from the selfishly optimal choice for your parents' genes.

Example: Suppose you will have 6 surviving children if you elope, but only 3 if you do not. If you elope, however, your siblings will have 12 children between them, but if you do not, their total will be 16. Then your genetic payoff from eloping (6 children plus 12 nephews and nieces who count for half equals 12) exceeds your genetic payoff from not eloping (3 children plus 16 nephews and nieces equals 11). But your parents maximize their genetic payoff if you stay, because (6+12)=18 grandchildren is less than (3+16)=19 grandchildren.

Thus, we should expect to see parent-child disagreement primarily when there are externalities for siblings. (Though the same principle holds of course if your parents are young enough to have more children, or if your behavior affects the reproduction of your extended family too). This is an elegant explanation for parents' hostility to promiscuous daughters. But it applies just as well to parents' hostility to sons' engagement in high-risk activities that might make his name (hence the son's temptation) or embarass the whole family (hence the parents' resistance). It also accounts for the mundane fact that parents push their kids more toward financial success than happiness: Every successful child frees up resources to help other siblings reproduce too.

But what about parents of only children? Aren't they often even more meddlesome? That's a tough challenge. My best answer is that humans evolved in conditions when almost everyone had large families, and where everyone knew everyone. Just as we now consume sugar and salt to excess (or so I'm told) because these were scarce during our evolutionary history, we ride our kids too hard today because we evolved in conditions when one bad kid could ruin the lives of his ten brothers and sisters.

Now if I could only explain why my identical twins can't agree on whether to watch Shrek 2 or Thomas the Train...


Comments and Sharing





COMMENTS (8 to date)
jaimito writes:

The methodology seems right, but what may be the reason why a girl eloping with a boy "from a lower station" would double the number of her surviving children? All along human history (the last 100 years being an exception), higher station meant more access to resources and more surviving children.

Parent know from experience things that eloping adolescents do not, like the high probability of being left by the eloper, being sold and or transferred to third parties, to slip in the slippery slope of social degradation. Eloped girls rarely if ever end married and well established.

It is interesting to me that dilemmas of Victorian novels a 150 years ago seem to be relevant today.

Mark Horn writes:
Suppose a headstrong daughter defies her parents to marry beneath her station. Is she the only person whose genes are affected by this decision? Hardly. There is an obvious negative externality for her siblings, who will see their opportunities in the marriage market diminish.
I'm not able to see the obvious negative externality. If there are X potential husbands in the daughter's "station", and Y sisters, then by marrying out of station, there are still X potential spouses but now Y-1 siblings. Each of the sisters has a slightly larger supply of potential husbands. How is this negative? I don't see how a sister marrying beneath her station has any impact (positive or negative) on her brothers.

Note my normal disclaimer: I'm not an economist and I don't play one on TV. I'm here hoping to learn.

Ramon writes:

"I'm not able to see the obvious negative "externality"

Courtship is a family enterprise. If the sister marries down, She is signaling low quality of the family's genes, which reduces other siblings' chances of getting a high quality partner.

Diseases, bad decisions, everything any member of the family does gives information to potential partners.

Robert Schwartz writes:

The idea of rebelious youth originated in romanticism after the French Revolution, was promoted by writers in the 19th century and became a staple of marketing in the 20th. It is not a time honored tradition, and there is no particular reason why it has to continue.

Mark Horn writes:
Courtship is a family enterprise. If the sister marries down, She is signaling low quality of the family's genes, which reduces other siblings' chances of getting a high quality partner.
Really? I married a woman with 8 siblings. At no point do I remember deciding that the quality of her siblings' spouses impacted whether or not I was going to marry my wife. Nor do I recall any of my friends who have married commenting on the spouses of their future in-laws.

Is there data to back this up or is this one of those austrian "derived by logic" things?

Paul N writes:

WTF? Maybe you should re-read Becker instead of War and Peace!

I resent the implication that the parents are smarter than the kids about what's best for them - especially in the case of kids old enough to get married! I was rebellious because my parents were wrong - and 10-15 yrs later I still think they were wrong!

jaimito writes:

Paul, Can you know where would you be now if you followed your parents' advice? You can live only once, so no conclusion can be drawn. I cannot accept your opinion, because the recognition of the possibity that your parents were right and you wrong would cause a psychological pain for you.

At age 5: Father is a Giant. I want to be like him.
At age 8: Father knows everything.
At age 10: Father is OK.
At age 15: I am ashamed of the Old Man in front of my friends.
At Age 20: He knows nothing. A real monster.
At Age 30: You know, the Old Man is totally senile, but sometimes I like to hear his opinion.
At Age 40: Father was OK and in most cases, he knew what he was talking about.
At age 50: Father was a Giant.
At age 60: I want my Poppa!

Tracy writes:

Can't parents and children disagree simply because they have different takes on the world?

A parent cannot truly know what is going on their child's mind and vice-versa. Furthermore everyone has a unique history of their own and holds different sets of information. And, if we have free will, even with the same set of information we could make up our minds differently. Different people can also have different discount rates.

A parent opposing the poor suitor may see the suitor's poverty but not his affectionate care or his sly wit. The parent and the child may hold different opinions about the value of money vs. character.

Also different viewpoints can bias you. The parent would get the possible benefit of the rich suitor's support without having to live with the guy. A selfish parent, or one lacking in imagination, may oppose a poor parent out of self-interest or out of a different balancing of their interests against their child's.

And a parent has probably had more opportunities to encounter the knowledge of grief than their eager young son day-dreaming of joining the guerillas.

Comments for this entry have been closed
Return to top