Modern molecular biology has allowed us to look ever more closely into the genetic changes associated with human evolution. A recent research project used this technology to examine a possible relationship between diet and genome.
We're accustomed to a diet high in starchy foods (potatoes, pasta, & rice, for example). However, some populations of modern humans (eg Inuit) have traditionally eaten diets high in protein, with only small amounts of starch. Shadaf Shadan (2007) summarises the findings of a project that examined the relationship between dietary starch and the number of copies of a gene that codes for salivary amylase, the enzyme that digests starch.
People differ quite markedly in the number of copies of this gene, which is called AMY1. The researchers found that the extra copies were functional: the more copies an individual has, the more salivary amylase they produce. But is there any relationship between past diet and the number of copies of AMY1? And does having multiple copies of AMY1 confer any selective advantage?
To answer the first question, the research team collected copy-number data from two groups of people. The first comprised four different populations with a diet low in starch, while the second was made up of three populations with high-starch diets. Both groups included people from Asia and Africa i.e. both contained people from different geographic areas.
The results? The high-starch group contained twice as many people with at least 6 copies of AMY1, compared to the low-starch group. This couldn't be explained by geographical differences, and the researchers concluded that the copy-number differences were the result of natural selection for a high AMY1 copy number.
And the selective advantage? The researchers suggested that someone with more salivary amylase would be better able to digest starch while chewing their food, and thus maximise the amount of glucose available for absorption.
Reference: S. Shadan (2007) You are what you ate. Nature 449: 155