Genetic Paradoxes

 

             Homosexuality is an example of a genetic paradox.  Homosexuality would seem likely to die out of a population because of reproductive failure.  Yet, comparative primatologists have studied chimpanzees and other primates and determined that homosexuality motivates non-dominant males to stick around their natal groups enhancing the survival of their nephews and nieces against the hazards of the jungle including tribal territorial warfare by other troops of chimpanzees—a biological basis for acceptance of “gays in the military” perhaps.

            A paradox occurs when two seemingly conflicting ideas both turn out to be valid.  Genetic Paradox refers to a harmful trait that has been preserved by inheritance for long periods of time and many generations.  Sickle cell anemia, mostly a disease of blacks, is one of several types of hemolytic anemia which seem to be paradoxical in that they persist in populations in spite of obvious health, reproductive and survival disadvantages.  It turns out that these hemolytic anemias confer some resistance to malaria and therefore persist in populations heavily exposed to malaria.  Sickle cell anemia is the easiest of these diseases to understand.  When it is inherited from both parents the disease is severe and does not permit survival to reproductive age.  When the sickle cell trait is inherited from only one parent, the trait is detectable by the sickle shaped red blood cells; but it is compatible with normal health, as illustrated by the fact that people with the trait are eligible for military careers in the United States armed forces and suffer no health deficits or even deficits in maximum athletic fitness.  Mathematicians calculated the incidence of this gene in a geographical area of prevalent malaria, where presence of the gene maximizes health for the population as a whole.  The incidence of this gene is exactly what the mathematicians postulated.

             Evolutionary biology has something to tell us about the rising incidence in all ethnic groups of type II diabetes, so called “adult onset diabetes”, especially the fact that this disease is occurring in younger and younger people.  Insulin is necessary in everybody for storing food for future use.  Insulin is not necessary to sustain exertion that is already occurring.  The genes that promote type II diabetes have evolved to become “thrifty genes” because they promote hair trigger insulin production resulting in more food being stored, which promotes obesity.  This genetic make-up has extra survival value in times of famine.  But in the absence of famines, the result is often like that of the Pima Indians of the American southwest who were early on identified as having a high incidence of diabetes and obesity when modern lifestyles led to little exercise and almost no famines. 

            Only recently has it come to light why groups of European ancestry have a remarkably reduced incidence of type II diabetes.  Europeans have the longest history of settled agriculture with stored food and social organization minimizing famines. And Europeans who remained in Europe have the lowest incidence of diabetes, those in North America an intermediate incidence and those in Australia a higher incidence (8%) than others of European extraction but still much lower than all other ethnic groups.  This phenomenon is explained by the stratification of European society in pre-colonial times.   The upper classes intermarried among themselves resulting in selection of those without the thrifty genes advantageous to those more at risk for famine. They had the least motivation to emigrate.  Australia was populated by prisoners who served their sentences there and were not given passage home--commandeered colonists.  As they became successful colonists the thrifty gene which they carried in a higher amount than other Europeans ceased to have the previous survival value and contributed to an increase in type II diabetes.

The island, Nauru, in the South Pacific was populated by Polynesians selected by     surviving famine on long canoe journeys to their new home.  Conditions on Nauru remained difficult until after World War II when the small population was “blessed” with large individual royalties for mineral rights from a multinational company.  The ensuing motor scooters eliminated exercise and helped to cancel the previous benefits of thrifty genes.  Now 50% of the entire population of Nauru have diabetes, a world record.  It will take several generations until Nauru has a more ordinary incidence of diabetes.  It is hard to imagine an education effort by public health officials having much impact.  I say this as a physician who is compelled professionally to try to induce major lifestyle changes seemingly against all odds.

            So far we have talked about genetics fostering what appears to be disadvantageous inheritance in hemolytic anemia, homosexuality and diabetes.  Let us speculate about the tendency we have to become addicted to various substances.  Can there be any countervailing advantage associated with the ability to become addicted?  Yes, addicts tolerate fatal doses of the substances to which they are addicted without even getting sleepy.  Imagine vegetarian animals surviving a drought because they became tolerant of toxic chemicals in a plant that was also surviving the drought.  If there were few or no choices of other plants to eat, addiction would be a small price to pay for the ability to thrive by eating such a plant.  Opium poppies have edible leaves, tasty seeds, nutritious bulbs and morphine throughout the plant.

             These principles of evolutionary biology and genetics have strong explanatory power in helping us understand the world in which we live and in which we must survive, if we survive at all.

John A. Frantz, M.D.

July 2, 2003

 

The right time to become a vegetarian

 

       It takes two or three times as much land to support a meat eating person as it does to support a vegetarian.

       Mankind has been slow in solving the population explosion except in the developed world where women are educated.  Incidentally Ireland and Spain, where women are educated, have just as low birthrates as Germany and Scandanavia.  Education trumps religion or ethnic status when it comes to personal decisions about family size.

       When the population crunch comes the more of us are eating meat and can thereby switch to become vegetarian the fewer people will have to starve.  Meanwhile, let us send teachers everywhere to educate women.  Some education will rub off on the men and that will be “the icing on the cake.”

John A. Frantz, M.D.

June 19, 2003