1. Gene‑Centered Evolution

- Following Dawkins, evolution operates at the level of genes and gene‑teams, not organisms.

- “Fitness” is value‑neutral: a trait is fit only if it increases gene replication.

2. Polygenic Traits and Conditional Advantage

- Most traits arise from interacting gene complexes, making fitness context‑dependent.

- Harmful traits can persist when they provide situational benefits.

3. Adaptive “Diseases”

- Classic cases:

- Sickle‑cell trait → malaria resistance.

- Tay‑Sachs carrier state → hypothesized TB resistance.

- Cystic fibrosis carriers → partial cholera/TB protection.

- These illustrate heterozygote advantage: harmful in one form, beneficial in another.

4. Environmental Fit as the Determinant of Surviva ...