If It’s Becoming More Common, It’s Not Genetic!

Don’t get me wrong. I think that the Human Genome Project was a great idea. How­ev­er, I don’t think that genet­ic stud­ies are going to help us unrav­el our main caus­es of death and dis­abil­i­ty in the Unit­ed States. That’s because they are large­ly the result of our food, not our genes. You can tell this from the sim­ple fact that the rates of these dis­eases go up and down, depend­ing on how a pop­u­la­tion eats.

The rate of tru­ly genet­ic dis­eases (such as hemo­phil­ia or cys­tic fibro­sis) stays remark­ably sta­ble in a pop­u­la­tion from one gen­er­a­tion to the next. The only way it could increase is if there were a sud­den wave of immi­gra­tion of peo­ple car­ry­ing the gene (in which case, the dis­ease would most­ly be in the immi­grants and their chil­dren) or if the peo­ple with the gene sud­den­ly became much more fer­tile (which is unlike­ly).

When you see the rate of a dis­ease go up and down dra­mat­i­cal­ly with­in the space of 10 years, you know for sure that the cause of that change is envi­ron­men­tal, not genet­ic. The clas­sic illus­tra­tion is the sharp decline in heart dis­ease in Nor­way dur­ing World War II. After the Nazis invad­ed Nor­way (and stole a lot of their farm ani­mals), the Nor­we­gian pop­u­la­tion had to shift to a low-fat, plant-based diet. As a result, the dis­eases of afflu­ence (heart dis­ease, type 2 dia­betes, mul­ti­ple scle­ro­sis) became much less com­mon. The rates of those dis­eases went right back up again after the war end­ed and peo­ple went back to their old ways of eat­ing.

Anoth­er clue to whether a dis­ease is genet­ic or envi­ron­men­tal comes from its geo­graph­ic dis­tri­b­u­tion. If a dis­ease is most com­mon in an area with small gene pool, it’s like­ly to be genet­ic. Exam­ples include the hered­i­tary deaf­ness that was once com­mon on Martha’s Vine­yard and Tay-Sachs dis­ease in East­ern Euro­pean Jews and French Cana­di­ans. These are reces­sive gene dis­eases. You can get the dis­ease only if you got the same defec­tive gene from both par­ents, which is most like­ly to hap­pen if they are relat­ed to each oth­er.

On the oth­er hand, if a dis­ease is most com­mon in an area whose pop­u­la­tion came from a wide vari­ety of immi­grants, then you can bet your bot­tom dol­lar that the under­ly­ing cause for the high rate of the dis­ease is envi­ron­men­tal, not genet­ic. The clas­sic exam­ple of this is Parkin­son dis­ease, which is most com­mon in Buenos Aires, Argenti­na. Although there may be some genes that pre­dis­pose a per­son to Parkin­son dis­ease, espe­cial­ly the ear­ly-onset form, the fact that the world’s high­est rate is in a pop­u­la­tion made up of recent immi­gra­tion from many dif­fer­ent places tells me that the major risk fac­tor is some­thing in the envi­ron­ment. Con­sid­er­ing that the peo­ple of Buenos Aires also eat more beef than any­one else in the world, I’d be will­ing to bet that the envi­ron­men­tal fac­tor is red meat con­sump­tion.

Pho­to by Inter­net Archive Book Images

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