MORE THAN YOU WANT TO KNOW ABOUT PATERNITY

Anna Nicole Smith November 28, 1967 – February 8, 2007

[It’s August.  Let’s take a break from anything political.  This Monday’s Archive  was originally published in TTP on April 11, 2007. Everyone back then knew of notorious Anna Nicole whose life had tragically ended two months earlier.  Yet her promiscuity turned out to be quite instructive. It still is.]

TTP, April 11, 2007

I can’t pass this one up.  DNA testing that shows among Anna Nicole Smith’s multiple lovers, a fellow named Larry Birkhead is the father of her daughter provides such an exquisitely teachable moment about paternity – well, it’s simply impossible for me to resist.

This is going to be fun.  We’ll start with a discussion of what scientists delightfully call “sperm wars.”  Let’s first discuss those conducted by chimpanzees.  They give the phrase “flooding the zone” a whole new meaning.

Chimpanzees are our closest primate relatives with whom we share a common ancestor.  That common ancestor lived a long time ago.  The human-chimp split took place around 5 million years ago (5 mya).

Chimps and humans have, however, retained certain basic behavior patterns in common – such as patrilocality.

Almost all primate species are matrilocal:  the females stay in their home territory while the males disperse out of the territory at puberty.  Except for chimps and humans which are patrilocal, where the female leaves her home community at puberty and joins another (in traditional human societies a wife moves away to live with her husband’s family).

Thus males form the basis of a home territory and much of chimp society is based on males defending it.  Any male from another community found in their territory is immediately killed.  Males frequently conduct raids on nearby rival communities with the purpose of exterminating the community – killing them all.

Sound bell-ringingly familiar?

But for other behavior patterns, chimps and us are really different.  Like sex.

The evolutionary purpose of sex, of course, is the replication of DNA or “reproductive success.”  Here’s how the chimps do it.  When a female ovulates, she advertises her condition with large pink swellings around the target area.  She then happily and publicly copulates with every male in her community.  Researcher Jane Goodall once observed a female copulating 50 times in one day.

Since male chimps will kill an infant he thinks is not his, the females strategy is to let all the males think a subsequent baby could be his:  “confusing paternity” is what biologists call it.

What, then, is the male strategy for best ensuring his genes get replicated?  Evolving huge testes.  Relative to body size, chimp testes are ten times the size of a man’s, with enormous sperm production to match.

Given the females’ promiscuity, the male who produces enough sperm to flood out his competitors’ wins in the replication race.  Thanks to “sperm wars,” chimp society is dominated by one alpha male and three or so of his allies who are the physically strongest and most aggressive of the community.  DNA paternity testing in chimp communities shows on average that the alpha male accounts for some 36% of all conceptions, while his allies account for another 50%.

Male chimpanzees are far larger than females, as were the earliest hominids, Australopithecines (the first walking apes, 4.4 mya) and Homo habilis (first tool-maker, whose brain size doubled that of chimps, from 400 to 800 cc’s, 2.5 mya).  This “sexual dimorphism” changed with Homo ergaster around 1.7 mya, the first hominid recognizably human.

Ergaster, unlike his ancestors, was capable of sweating as he had lost most body hair.  He was tall – a six-footer, with a barrel chest and small belly who ate a lot of meat (thus didn’t need a big belly to digest a diet of plants).  And his dimorphism was much reduced, for females had gotten bigger.

This reduction of dimorphism signals that the greatest revolution in human society was occurring:  pair-bonding.  One man mating with (usually or at least) one woman, the nuclear family as the foundation of a human community.

As great as the benefits of pair-bonding, the risks are great also – especially for the man, for if he is cuckolded, another man’s genes are replicated, not his.  Thus societies place a welter of imaginative restrictions on female sexual activity in attempts to solve the Eternal Paternal Problem:  “mother’s baby, father’s maybe.”

This ancient male fear of his wife’s baby not being his remains today, and with justification.  Human geneticists estimate that the biological fathers of at least 5% or more of babies born if the US are not who the mother says they are (the “father of record”).

Anna Nicole listed her lawyer/boyfriend Howard K. Stern as the father of record on her daughter’s birth certificate.  Yet she made no pretensions about being sexually monogamous.  Her promiscuity raises the question of sperm competition during her daughter’s conception.

It turns out such competition is surprisingly common.  Evidence for it is provided by the phenomenon of heteropaternity with fraternal twins.  Identical twins result from the splitting of one egg.  Fraternal twins result when the mother releases two eggs and both are separately inseminated.

Normally, the same man’s sperm inseminates both eggs.  DNA testing in paternity cases shows that in some 2.4%, the fraternal twins have different fathers, meaning the mother was impregnated by (at least) two different men within less than a day or so (sperm rarely survive for more than 48 hours and usually less).

Greek mythology celebrates heteropaternity with the legend of the twins Castor and Pollux (now the constellation of Gemini, the twins).  Their mother was Leda, Queen of Sparta.  Castor’s father was King Tyndareus, while Pollux’s was the god Zeus, who took the form of a swan to seduce her.

Evidently Howard K. Stern and Larry Birkhead (and possibly others) had sex with Anna Nicole in the same 24 to 48 hour time period of her daughter’s conception.  A sperm war then took place in her reproductive tract, direct competition between rival sperm fighting to fertilize her egg.

Larry’s won.  Now you know.