GED5-short

Introduction

  • Fitness, selection, and social evolution by Matthew Cobb

Survival of the Fittest

  • Concept popularized by Herbert Spencer

  • Implies conflict and struggle in survival

  • Complexity of evolution is often overlooked

Understanding Fitness

  • Questions raised:

    • What is 'fitness'?

    • Who are 'the fit'?

    • What is selected?

Definitions of 'Fitness'

  • Fitness is not just about physical traits:

    • Small gut and big arms?

    • Being strong?

    • The relative probability of survival and reproduction of a genotype

  • Difficult to quantify precisely

Factors Influencing Fitness

  • Fitness varies based on:

    • Environmental conditions (varying in time and space)

    • The number of copies of an allele

Case Study: Sickle Cell Disease

  • Homozygotes exhibit health problems like anemia

  • The sickling variant persists due to advantages in malaria zones:

    • Heterozygotes are less likely to get malaria

    • Heterozygote individuals are more 'fit' in certain environments

Historical Context

  • 1949 discovery of sickle cell trait by Linus Pauling, Itano, and others:

    • Described the reversible shape changes of erythrocytes (red blood cells)

    • Approximately 8% of American Negroes possess sickle cell trait with no severe health issues

  • 1957 findings by Dr. V. M. Ingram unveil genetic mutation affecting hemoglobin:

    • Identified the specific amino acid change from glutamic acid to valine in sickle cell hemoglobin

Genetic Engineering and Future Perspectives

  • 2030 possibilities with CRISPR/Cas9 for a curative approach to sickle cell disease:

    • Challenges and the potential for genome editing applications in treating SCD

The Debate Over Selection

  • Levels of selection:

    • Species, groups, families, individuals, or genes?

  • Evolution signifies changes in allele frequencies

  • Selection operates on individuals expressing phenotypes:

    • These individuals interact differentially, affecting gene transmission

Evolutionary Theories and Concepts

  • Darwin's struggle with social structures like sterile neuters in insect communities:

    • Suggested selection applied to families as well as individuals

  • Definition of altruism:

    • Behavior benefiting another at personal cost

Hamilton's Rule

  • Introduced by Bill Hamilton:

    • Differentiated 'Darwinian or direct fitness' and 'inclusive fitness'

    • Altruism can be explained through kin selection, where the cost (c) to the performer is outweighed by the benefit (b) to the recipient, based on relatedness (r)

Social Insects and Altruism

  • Structure of social insects with only the queen reproducing

  • Naked mole rats as examples of mammalian eusocial behavior

  • Haplodiploidy in Hymenoptera:

    • A scenario where females are diploid and males haploid allowing for increased genetic relatedness among siblings compared to own offspring

Challenges and Complexity in Social Evolution

  • The relationship between relatedness, ecology, and species evolution is intricate

  • Hamilton’s insights provide a framework for understanding social evolution but do not fully explain all phenomena

Key Takeaways

  • Definitions and implications of fitness

  • The example of sickle-cell anemia shows the advantage of heterozygotes

  • Differentiating levels of selection is crucial in understanding evolution

  • Altruism challenges traditional viewpoints, potentially solvable through inclusive fitness and kin selection

  • Social structures in insects and mammals highlight complexities in evolutionary biology

Conclusion

  • Continual research and debate are crucial in understanding the evolution of social behaviors and fitness. Next topic: Genomes.