Angelina Jolie and Brad Pitt are classic "beautiful people." By now you know they are going to have a baby. What sort of child will this be? Handbag.com offers you a projection:
Not half bad. Certainly more traditionally beautiful than the Brit Rock look-alike produced by Jennifer Garner and Ben Affleck.
Why are Brad Pit and Angelina Jolie so beautiful? Neither of them were raised in dire circumstances, but likely they have a "genetic leg up." In any given population there will be a genetic load, a number of deleterious alleles which decrease average population fitness from the idealized maximum. But, there will also likely be variation of genetic load. We know this intuitively because some individuals are "less fit" than others, eg., an individual who carries two copies of the Cystic Fibrosis allele. But many deleterious alleles which we carry do not have such prominent effects on our phenotype, but may nevertheless detract from our ability to reproduce with the graceful ease that a true Intelligent Designer might have gifted us with.
Some of these deleterious alleles are lethal recessives. The estimates for the number of lethals that a human carries usually do not go much above 30 (and are often below 10). The rationale is that the rate of spontaneous abortion among first cousin matings, and the rare sibling matings, would be far higher above the population median than they are. Since relatives are likely to carry similar lethals there is a great likelihood for intersecting loci of lethality. As the number of spots in the genome of these lethals increases the mathematical possibility of generating offspring without two lethal copies of an allele on all the loci become neglible .1 Please note that this small number of lethal loci also implies there is likely to be variance within families because of sampling effect (some siblings will get two good copies, some only one). In The Mating Mind Geoffrey Miller contends that this sibling variance is crucial in dumping deleterious alleles from the gene pool every generation that are built up by mutation (ie., less healthy siblings do not reproduce to the same extent, if it at all).
It is important to note that "dominance" is often not perfect, and even if one "good copy" of a gene can mask lethality, its function might be suboptimal. In concert with the host of other deleterious alleles this might result in developmental stress and susceptibility to infection because of lack of genetic health. This is an expectation, not a guarantee. A good throw of the genetic die helps, but it is not sufficient for preternatural beauty.
But how can Brad Pitt and Angelina Jolie save the world? Well, the title was hyperbolic, but one of the concerns of the late evolutionary biologist William D. Hamilton was that the human population was not removing deleterious alleles from the gene pool fast enough. The reason is that humans are extremely complex contingent organisms with large genomes and low reproductive values reduces the ability of selection to sift through those genomes. Hamilton was concerned about a mutational meltdown, as the number of deleterious alleles increases, the mean fitness decreases. As mean fitness decreases there is potentional for reduced population size, at which point random genetic drift can swamp selection against deleterious alleles. As more and more deleterious alleles build up and the genetic load increases the population keeps decreasing and random genetic drift becomes more and more powerful vis-a-vis natural selection.
Many biologists do not share Hamilton's concern, in The Cooperative Gene evolutionary biologist Mark Ridley proposes that spotaneous abortion suffices to purge the gene pool of deleterious load. If individuals who carry deleterious alleles survive to adulthood the theory is that they are more likely to produce a fetus which will be aborted because of developmental problems. But spotaneous abortion isn't the only option, last week Elizabeth Weil in The New York Times Magazine covered the controversy around "wrongful births." Even today abortions are reducing the number of children who are born with Down Syndrome, but this is not really purging genetic load since it is a trait that is caused by massive de novo chromosomal abnormalities which would not result in any contribution to the gene pool in any case. On the other hand, diseases like Tay Sachs are being prevented by genetic testing so that heterozygotes do not marry, or at least abort any fetuses which are homozygous for the abnormality. In this way it seems that the fitness of Tay Sachs carriers is heightened, and so the frequency of the Tay Sachs allele is greater than it would be because of modern genetic science. The key is whether heterozygotes are equivalent to normal homozygotes. Some people argue that there are phenotypic differences between Tay Sachs heterozygotes and normal homozygotes. But this is just the tip of the iceberg, the postgenomic era will likely usher in a wide range of tests, not just for monogenic Mendelian disorders, but also for genes that suggest a propensity in concert with other genes for particular traits. It maybe that genes have powerful epistatic effects, or, their expression is diffentially mediated by a given environment, and so on. It is often stated that the ethical dilemnas posed by the new genetic science will be far more complex than the science itself, but I am not so sure as we move past testing for Mendelian traits toward the cheap sequencing that might give clues as to the shape of quantitative traits. How many parents would pay to get that extra edge for their child, a notch up the normal distribution? If life does not begin until late in the pregnancy, then the first trimester could become a gambler's playground and the current ethical conundrums spawned by sex selection might be but the faintest blood in the water.
As for Angelina and Brad...being beautiful might just be the grace they get to avoid many of these questions, their faces being manifest advertisements for their health and the reason for their wealth.
Addendum: Please note that there is a lot of controversy around many of the terms like "fitness," or the possibility that fitness is heritable (or not). Additionally, though I believe there is a lot of circumstantial evidence for the correlation between beauty and genetic health...it is still circumstantial.
1 - If one of the grandparents has a lethal on a locus, then each viable offspring has a 1/2 chance of carrying that lethal as well. Assuming that the spouses of the siblings don't carry the lethal allele then each grandchild has a 1/4 chance of carrying that particular lethal allele (coefficient of relatedness here is 1/4, so that makes sense). For any two random grandchildren there is a 1/16 chance for a carrier + carrier pairing. 1/4 of the offspring would be inviable. So, multiplying out the independent probability of a 1/16 chance for carrier + carrier matings * 1/4 chance of the lethal combination, you have a 1/64 chance of the lethal reappearing in great-grandchildren assuming a first cousin mating. Or, to be optimistic, a 63/64 chance of the lethal being masked. Pretty good, huh? But what about other loci? The chance are independent, so you would note that as (63/64)n, as n approaches a higher number the probability of "missing" a hit on all loci starts to drop fast (a "hit" would be a homozygous lethal combination). At 45 loci you reach below 50% expectation of a miss on the all the loci due to first cousin marriages. The numbers for siblings are even more horrendous. And this doesn't take into account that there is another grandparent in the picture...with their own unique bundle of dirty genes.
well, of course Hamilton is right: look at the increase in peanut allergy or myopia.
perhaps superbiology and the transhumanists will be allowed to save the day. ;)
Insh'allah Matoko, don't tantalize us.
Razib, you talked about genetic load. RPM had a post a while back where he questioned the usefulness of Haldane's equation for genetic load, L = (Wopt - v) / Wopt. The gist is that v is just an algebraic artifact used to calculate changes in relative allelic frequency under selection, and doesn't really measure anything outside of that mathematical context. So Haldane's L doesn't really seem to refer to anything in the real world.
It makes sense to me, and I was just wondering if you'd read the post and what you think.
though I believe there is a lot of circumstantial evidence for the correlation between beauty and genetic health...it is still circumstantial.
Also, most psychologists don't distinguish people who are pretty, beautiful, etc., from people who are sexy, seductive, etc. Angelina sure looks healthy, but she looks too dangerous and manly to be beautiful. Her features are feminine enough to convince us she's all woman, but the subtle masculinity in her features, gaze, & demeanor tell us that she's a not some princess or angel but a panthress.
When young guys are in their "I want hot sex now" mode (and that's most of the time), they fixate on dangerous Angelina & similar folks. Pick up a "lad mag" and see (or watch Tomb Raider and Aeon Flux). When they think of the safe, pretty wife they want, then it's someone more decidedly feminine and often lighter in skin & hair color.
It's the old selfish gene view of the mistress-wife preference. When we want hot one-night sex, we want someone wild and forward, which are the qualities that Angelina's popular persona exudes -- though if you saw her on Inside the Actors Studio, you saw that in reality she's more passionate than wild, and quite disarming.
It makes sense to me, and I was just wondering if you'd read the post and what you think.
the critique is good, and haldane himself said "fitness is a bugger." *shrug* you got something better? :) i could have avoided the issue i guess by using fluctuating asymmetry as a proxy for the fitness. there are clearly some alleles which are contextually 'deleterious' and some which have unambiguous physiological effects that are problem in 95% > of circumstances.
agnostic, beauty is a composite of vectors, not a scalar....
very good, agnostic--i think we should start calling this "the ivanhoe effect"!
razib, what do you think?
I think in cinema and literature the dark grrls are the bad grrls, dangerous, wicked.
In that old movie Joan Fontaine is the blonde saxon ice princess and Elizabeth Taylor is the exotic, witchcraft-accused, dark-haired jewess.
Guess who winds up with Ivanhoe?
Haha, good call Matoko.
Razib, "beauty" and "danger" should be orthogonal. Audrey Hepburn, a cherry blossom -- not dangerous. A bully ready to pound your face in, an approaching tornado -- not beautiful. But if you drew a new vector that's 45 degrees b/w the beauty & danger vectors, it would be what I'm talking about -- equal magnitude components of beauty and danger. Call it... I dunno, "thrill," for lack of a better word. A bombshell dominatrix would be on it. Angelina's probably on a similar vector, though one w/ a slightly larger beauty component than danger component.
(I'm using "danger" for what aestheticians confusingly call "sublime.")
I think in cinema and literature the dark grrls are the bad grrls, dangerous, wicked.
yes, but the thing is to remember variance in cultural stereotypes. in mid-to-late 18th century england blondism was associated with lower class status, and dark hair with the aristocracy.
errr---not after the saxons. ;)
and, i hardly think Sir Walter Scott concieved of Rebbekah as a blonde.
the saxon aristocracy was demolished by the normans...who were a mix of scandinavian and french (. so take that for what it's worth. the Restoration preference for dark hair was probably a function of charles ii's personal preference, and his mistress barbara de villiers.
so, rowena is decribed as a saxon princess in Scott's Ivanhoe. Shouldn't she be blonde?
this is pre-restoration--the Age of Chivalry. ;)
Shouldn't she be blonde?
well, no people are more than 50% blonde by my definition of blonde (at least as adults). also, there is strong evidence of admixture with indigenous british females even in germanic regions of england like east anglia. so, if i had to bet, i would be against it, that is, less that 0.5 in probability, even if far higher than expectation across the channel.
spoiler. >:(
Using Brad Pitt and Angelina Jolie as examples of a fitness model is fun, especially since it complicates any simplistic connection between beauty and genetic health, and also shows huge flaws in any notions of good girls vs bad girls in mate preference. Consider:
Brad Pitt is 43, not a lusting teen, and yet he tossed over presumably safe, wifely women like Gwyneth Paltrow and the forever bland Jennifer Aniston for hot babe Angelina Jolie. In addition, he never had children with either Aniston or Paltrow, but is expecting his first child with Jolie. And although Jolie may be genetically healthy, she had a very troubled upbringing (and once had dreams of being a funeral director), has an odd fascination for knives and blood, and is deeply estranged from her father. Still none of this has prevented her from being regularly selected as one of the sexiest women alive by both men and women.
By the way, I should also add that wife-mistress preference says little to nothing about who has a better chance of having offspring. Simply put, who you marry is not necessarily the same thing as who you have children with. Particularly before birth control became more widely available or reliable, the odds were good that young guys having hot sex with dangerous babes would end up being fathers, and that enough of these offspring survived to help guarantee that there would be successive generations that were as hot and dangerous as their forebears.
you are so handsom ....and beautiful angie........hm so perfect