How can evolutionary history help explain a human trait linked to disease?

Evolutionary history helps explain human traits linked to disease by revealing why natural selection has left the body vulnerable to certain conditions. Rather than viewing the body as a perfectly designed machine, Darwinian medicine examines how traits are shaped by trade-offs, constraints, and environmental mismatches.1

Evolutionary explanations often fall into six categories of vulnerability:1

• Environmental Mismatch: Traits that were adaptive in ancestral environments may cause disease in modern settings, contributing to issues like obesity and hypertension.1
• Balancing Selection: Sometimes, a disease-linked gene persists because the heterozygote (carrying one copy) has a survival advantage. For example, the sickle cell anemia allele provides protection against malaria in tropical regions, even though it causes severe illness in those who inherit two copies.2
• Trade-offs and Constraints: Bodies are subject to engineering limits; for instance, bones could be thicker, but that would make the body heavier and slower.1
• Protective Responses: Symptoms like fever or pain are often not diseases themselves but defensive mechanisms shaped by natural selection to protect the host.1