A Touch of Heterosis

When a movie star is billed as having "it" or "oomph," what she probably has is heterosis (hybrid vigor). At least, that is what Geneticist George D. Snell says. In the current Quarterly Review of Biology, Snell assembles evidence to show that superior qualities in humans, including physical attractiveness, are often due to heterosis, resulting from the crossing of two strains.

Dr. Snell describes heterosis in the case of swine (Hampshires crossed with Duroc Jerseys produced superior pigs). Since he cannot repeat the same experiment with people, he sifts a great mass of records to look for self-propelled experiments in human hybridization.

One of the most successful was made by the famous mutineers from the British warship Bounty, who settled down on Pitcairn Island in 1790 with some Tahitian women. The offspring of six mutineers and about a dozen women were examined in 1825 and found to be notably taller than either Englishmen or Tahitians. Some of them were strong enough to lift 600 Ibs. They were so fertile (an average of 9.1 children per family in the third generation) that they soon overcrowded the island. Other isolated racial crossings (which were not adversely affected by social disapproval) turned out almost as well.

England experienced another kind of hybridization. During the Middle Ages, small groups of peasants kept to themselves in isolated villages. Some were racially distinct; others became distinct because of inbreeding. During the 16th century these enclaves broke up. The mingling of blood, says Dr. Snell, may have produced the outburst of talent and energy that characterized the Elizabethan Age.

The U.S. is well known for hybridization. Dr. Snell lists many prominent Americans as being the offspring of crossed strains--e.g., Henry Ford was English-Dutch; Alexander Hamilton was Scottish-French; Theodore Roosevelt was Dutch-English-Scottish-French. Lists of famous Americans show a high proportion of mixed ancestry.

Dr. Snell believes that the U.S. has not yet felt the full benefit of heterosis. The peak year of foreign immigration was 1907, but many immigrant groups tend to marry among themselves for a generation or two. The groups are now breaking up, Dr. Snell says, and the U.S. may soon have an outburst of hybrid vigor comparable to Elizabethan times.

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