The study investigates the relationship between diet and the evolution of human amylase gene copy number variation. It finds that salivary amylase gene (AMY1) copy number is positively correlated with salivary amylase protein levels, and individuals from populations with high-starch diets have more AMY1 copies than those with low-starch diets. The level of AMY1 copy number differentiation is unusual compared to other loci in the genome, suggesting positive selection on this copy number variable gene. Higher AMY1 copy numbers and protein levels likely improve the digestion of starchy foods and may protect against the fitness-reducing effects of intestinal disease. The study also compares AMY1 copy number variation in chimpanzees and bonobos, finding that humans have significantly more copies than these primates, which may explain the higher salivary amylase protein levels in humans. The findings suggest that dietary shifts, particularly the increased consumption of starchy foods, have played a significant role in human evolution.The study investigates the relationship between diet and the evolution of human amylase gene copy number variation. It finds that salivary amylase gene (AMY1) copy number is positively correlated with salivary amylase protein levels, and individuals from populations with high-starch diets have more AMY1 copies than those with low-starch diets. The level of AMY1 copy number differentiation is unusual compared to other loci in the genome, suggesting positive selection on this copy number variable gene. Higher AMY1 copy numbers and protein levels likely improve the digestion of starchy foods and may protect against the fitness-reducing effects of intestinal disease. The study also compares AMY1 copy number variation in chimpanzees and bonobos, finding that humans have significantly more copies than these primates, which may explain the higher salivary amylase protein levels in humans. The findings suggest that dietary shifts, particularly the increased consumption of starchy foods, have played a significant role in human evolution.