Rethinking the starch digestion hypothesis for AMY1 copy number variation in humans

Area of Science:

• Evolutionary biology
• Human genetics
• Biochemistry

Background:

• Alpha-amylase (AMY1) exhibits copy number variation (CNV) across taxa, with humans showing higher AMY1 gene copies than nonhuman primates.
• Human AMY1 CNV is often linked to dietary starch content, suggesting adaptation for efficient starch digestion in the Homo lineage.

Discussion:

• Alpha-amylase plays a limited role in starch digestion, producing minimal glucose. Subsequent enzymatic steps and glucose absorption are rate-limiting.
• Other enzymes like sucrase-isomaltase and maltase-glucoamylase can digest starch independently, rendering alpha-amylase nonessential for this process.

Key Insights:

• Evidence challenges the hypothesis that increased AMY1 CNV in humans is primarily an adaptation to starch consumption.
• While natural selection may influence AMY1 CNV, starch digestion is unlikely the main selective pressure.

Outlook:

• Alpha-amylase is expressed in multiple human tissues beyond the salivary glands.
• These alternative expression sites may harbor roles of evolutionary significance, warranting further investigation.