Metabolic Enzymes

Lactase, Lactose Tolerance, and Health:

Lactose tolerance refers to the ability of some people, particularly of European descent, to digest this sugar, found in milk, even into adulthood. In the evolutionary past the gene for lactase, the enzyme that does the digesting, normally got switched off in adults. But one variant (known as an allele) of the gene that does the switching off instead leaves the system running, conferring adult lactose tolerance. That lets this allele’s bearers consume a diet rich in dairy products, a useful trick for a species beginning to domesticate milk-producing animals.  A richer diet lead to healthier adults and more children surviving to adulthood compared to their lactose-intolerant inhabitants, causing this gene to spread when this allele appeared..  Genetic analysis shows that lactose tolerance emerged between 5,000 and 10,000 years ago. In evolutionary terms, it is thus extremely recent. In human terms, though, that timescale means how it spread and how this process intertwined with the rise of dairy farming are lost in the mists of prehistory.

Genetic variation in the enzymes involved in the metabolism of drugs can have a huge impact on the efficacy and/or risks of a drug:  Genetic variation in the enzymes involved in drug metabolism