Before a bite of bread reaches your stomach, digestion has already begun. Your saliva contains amylase, an enzyme that breaks down starch—and humans differ considerably in how many copies they carry of the gene that produces it.
That variation offers a revealing example of how culture can change natural selection.
A 2024 study analyzed 533 ancient West Eurasian genomes, alongside modern genetic data. Over the past 12,000 years, versions of the amylase region containing extra gene copies became more common. Agricultural populations also generally carried more copies than populations traditionally dependent on fishing, hunting or pastoralism. The findings support selection associated with increasingly starch-rich diets. Research study. Nature
Well supported: gene duplication is an important source of human variation. Earlier research found that more copies of the salivary-amylase gene, AMY1, were associated with higher levels of the enzyme in saliva. Nature Genetics
Plausible but not fully established: extra copies spread because they improved energy extraction from staple crops, helping their carriers survive or reproduce. The genetic evidence supports adaptation, but it does not reveal precisely which physiological advantage mattered most.
Nor did farming invent starch digestion. Amylase duplications existed long before agriculture; farming appears to have favored some existing variation. Nature
Our ancestors changed what they grew and ate. Across generations, those choices helped change the biology they passed on.
