The Neolithic Revolution and the Evolution of Life Expectancy

1. The Neolithic Revolution and the Evolution of Life Expectancy Oded Galor “It is not the strongest of the species that survive, nor the most intelligent, but the one most responsive to change” Charles Darwin

2. Objectives • The origin of the rise in life expectancy since the Neolithic Revolution Natural selection vs. Technological advancements, income, education,… • The role of natural selection in the non-monotonic evolution of life expectancy in the process of development • The effect of differential timing of the Neolithic Revolution across countries and regions on the emergence of sustained differences in life expectancy across countries and ethnic groups

3. The evolution of life expectancy17,000 – 1,000 BCE

4. The evolution of life expectancyin the process of urbanization (England)

5. The evolution of life expectancyEngland, 1580-2000

6. Theories of Aging • The Mutation Accumulation Theory [Medawar, 1946] Aging is an inevitable outcome of the declining force of natural selection in older age Adverse mutations in the post-reproductive age have a smaller negative effect on the survival of the genes

7. …Theories: Evolution of Life Expectancy • The Antagonistic Pleiotropy Theory [Williams, 1957] Late-activating harmful genes may be favored by natural selection if they have a beneficial reproductive effects in early stages of life. (Pleiotropy - multiple effects of a single gene)

8. …Theories: Evolution of Life Expectancy • The Disposable Soma Theory [Kirkwood and Holliday, 1979] Optimal allocation of metabolic resources between reproduction and maintenance.

9. The Disposable Soma Theory Evolutionary trade-off between: Resources channeled toward: • current reproduction & • somatic investment  longevity & future reproduction

10. …The Disposable Soma Theory Evidence: • Longevity is correlated with resources devoted to cellular repair and maintenance • Capacity of somatic cells to carry out effective maintenance and repairs (e.g., DNA repairs, accurate gene regulation, tumor suppression, and antioxidants), governs the time taken for damage to accumulate [Kirkwood (1998), Williams and Day (2003)]

11. Main Hypotheses - rise in population density - domestication of animals - increase work effort - poorer nutrition (e.g., reduced meat intake, reduced mineral absorption by the cereal-based diet) • The Neolithic Revolution increased the extrinsic mortality risk

12. Source: Richard H. Steckel

13. Health Index • Skeletal infections - inflammatory responses to bacterial invasion • Iron deficiency anemia - nutritional deprivation, low body weight, chronic diarrhea, parasite infections • Dental health -- indicator both of oral and general health • Degenerative joint disease -- mechanical wear and tear on the joints of the skeleton due to physical activity • Enamel hypoplasias - enamel deficiency commonly found in the teeth of people whose early childhood was biologically stressful • Trauma

14. …Main Hypothesis • This deterioration in the health environment increased the evolutionary optimal allocation of resources towards somatic investment, repairs, and maintenance (e.g., enhanced immune system, DNA repairs, accurate gene regulation, tumor suppression, and antioxidants) Short-run: (the composition of the population is unchanged) Life expectancy declined Long-run: (an evolutionary process) Evolutionary advantage to individuals who were genetically pre-disposed towards higher somatic investment  Increased representation of individuals who are genetically pre-disposed towards higher somatic investment  Life Expectancy increases

15. …Main Hypotheses • The deterioration in the health environment: • triggered the observed improvement in life expectancy since the Agricultural Revolution • was a necessary condition for the dramatic recent improvement in life expectancy

16. …Main Hypotheses • Differences in the timing of the Neolithic Revolution across regions led to sustained differences in life expectancy across countries.

17. …Main Hypothesis The rise in the extrinsic mortality risk enhanced the genetic potential for longer life expectancy (i.e., life expectancy in a risk-free environment) enabled the dramatic impact of recent improvements in health infrastructure on the prolongation of life

18. Rapid Evolutionary Changes in Humans in the past 10,000 years • Lactose Tolerance • Variations in the ability to tolerate lactose across regions is inversely related to the differences in timing of the transition to agriculture across regions and thus in the domestication of dairy animals in the Neolithic revolution • Gluten Tolerance • Variations in the ability to tolerate a protein present in wheat, rye, barley, and some oats, first domesticated in the course of the agricultural revolution, is inversely related to the distance from the Fertile Crescent • Genetic immunity to malaria - Sickle Cell Trait • Variations in natural immunity to malaria is related to the engagement in slash-and-burn agriculture

19. …Rapid Evolutionary Changes in Humans in the past 10,000 years • 700 regions of the human genome have been reshaped by natural selection within the past 5,000 to 15,000 years Voight et al. (2006) • ASPM (a specific regulator of brain size in the lineage leading to Homo sapiens) arose in humans merely about 5800 years ago and has since swept to high frequency under strong positive selection Mekel-Bobrov et. al (2005)

20. Testable prediction • Populations that experienced the Neolithic Revolution earlier have higher life expectancy

25. Evidence (other species): • The effect of a rise in extrinsic mortality risk on life expectancy is ambiguous [Williams and Day (2003)] • Recent study: Guppies that were exposed to higher extrinsic mortality risk had a higher life expectancy in a risk-free environment (i.e., lower intrinsic mortality rate) [Reznick et al. (Science, 2004)]