Gene Expression

There are reports coming out that Angelina Jolie is going into labor. This is improtant, because last year Armand Leroi spoke about the possible relationship between beauty and low mutational load.

Leroi has posited that one way to decrease the effect of load is hybridization. The logic is simple: assume that each human carries multitudinous deleterious alleles, that is, nasty grams on particular genetic loci. If one assumes that these are predominantly recessive so that their negative implications really manifest themselves disproportionately when they are found in two copies, then mating between closely related individuals will increase the chance of two copies coming together because they’re more likely to be shared. For example, to use an extreme case, imagine that a mother and a son “do the deed.” If the mother carries 3 lethal alleles at 3 loci, the expectation is 1.5 for her son. But since genetics is discrete he’ll have an integer value between 0 and 3, with 1 and 2 being more common (you can imagine it as a binomial distribution, E(X) = 1.5, Var(X) = 0.75). Now, at any given locus the mother can pass one of the lethals to her son, so….

at locus 1 there is a 0.5 chance of a lethal
at locus 2 there is a 0.5 chance of a lethal
at locus 3 there is a 0.5 chance of a lethal

The chance that mother will contribute a lethal at any given locus in a mating is 0.5, so, at any given locus a mother X son mating would have a 0.5 X 0.5 change of lethality, or 0.25. So, at any locus there is a 0.75 chance of viability (non-lethality). But, each locus is independent, so multiplying across you get a 42% chance of viability. Not so hot. The same logic, to a far diminished level exists with cousins, and to a lesser extent with races (e.g., whites have a 1 out of 25 or so chance of being cystic fibrosis carriers, non-whites have a zero chance).

Does this apply to interracial matings? I don’t know, and I don’t think anyone does. The a priori logic is clear, but as I said the risk of deleterious recessives can drop off rather quickly with increased genetic distance and one might encounter genetic incompatibilities once one starts to outbreed far enough.

Which moves me to Jolie & Pitt. They are very beautiful people, with high levels of facial symmetry and well developed secondary sexual characteristics. Evolutionary psychologist Geoff Miller, and Leroi himself, have proposed that beauty is a marker for genetic fitness, and this genetic fitness is just a parameter which to a large extent reflects mutational load. In fact, Miller proposes that variance in mutational load between siblings is what allows our species to purge itself of deleterious alleles (the ugly unfit siblings don’t reproduce, serving as a flusing system for the gene pool). Leroi’s idea was that hybridization can mask deleterious alleles via dominance (that is, if two individuals are genetically dissimilar, then they presumably will not share many rare but very deleterious mutations across their loci). But, if you have individuals who are of low mutational load, voila, no need for gimmicks! There are 6 billion individuals in the world, it is possible that there are individuals with only a trifling mutational load compared to the human mean that walk amongst us. Note that though many very negative deleterious alleles are easily masked, heterozygosity is usually not perfect and mildly suboptimal. The human genome is large, and each locus is a crap shoot contingent upon the genetic conformation of one’s parents. But imagine the possibilities if beautiful mutation free (relatively) parents come together to produce progeny, the variance in probabilities imply that some of their children might be even less mutationally loaded! (3 de novo mutations per generation seems trivial)

In any case, I’ll be looking at the baby pictures…that’ll tell the tale if the child will be Leroi’s 191 deleterious allele marvel (as opposed to the mean of 300).


  1. #1 Boknekht
    May 21, 2006

    I don’t know how healthy their genomes are but, personally, what’s so great about Brad Pitt? The guy’s average. I think Richard Dawkins is handsomer than Pitt. And Jolie just digusts me(she’s bony as hell & her face looks like some sort of expressionless mask w/ nasty lips?) Call me insane or unaesthetic, but i wouldn’t have her if she gave herself to me. honest. I know, i know, they’re almost Gods to others, blah.

    Don’t know what their mutational loads are, but they ain’t impressin’ me, which is usual with actors & actresses.

  2. #2 zhimbo
    May 24, 2006

    To Boknekht: Evolutionarily speaking, beauty is an opinion poll. All indications are that Pitt and Jolie are “really hot” – Technically speaking. In an evolutionary sort of sense. As in, a large number of people wish to mate with them.

  3. #3 Monika
    May 31, 2006

    Honestly I must agree.
    Brad Pitt is quite short in stature and very thin looking. He looks ok in some movies, but when out of make up and having a bad hair day like the rest of us, he is just your average joe. I don’t know much about his personality, but the fact that he and Angelina Jolie adore each other is admirable. I adore my husband as well, even after 17 years together.
    Angelina Jolie is pretty than average though. One must argue the fact that the beauty shines from who she is, rather than just the exterior. If she was mean, rude and heartless I think her beauty would not appear, again we would have average.
    Hollywood is about “the lie”. Everything from looks to politics and in between is a lie in Hollywood, so to contemplate scientific fact on two people that are merely hypocrits (actors if you will) is frivilous.

  4. #4 hf2272
    May 31, 2006

    well, no one i know thinks jolie is hot or mildly attractive. personally, i think she looks weird. i do not know how she was on the hottest women list by any magazine.

  5. #5 Lilly
    June 5, 2008

    I wouldn’t say that Angelina Jolie possesses a high degree of “facial symmetry.” In fact, her very large lips when compared with her otherwise attractive, though unremarkable, features seem to be the main drawing point for the eye. Also, it is likely that Angelina received fertility treatments to conceive her soon-to-be-born twins, so the beauty/reproduction link may not hold in her case.

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