Question

J. B. S. Haldane once remarked that he'd be willing to lay down his life to save two brothers or eight cousins. Explain what he meant.

Short answer

J.B.S. Haldane's remark about being willing to lay down his life to save two brothers or eight cousins is related to the concept of kin selection and inclusive fitness in evolutionary biology. Kin selection is an evolutionary strategy in which individuals help their close relatives survive and reproduce, thus indirectly passing on their genes. Inclusive fitness accounts for an individual's genetic contribution to future generations through both direct offspring and the relatives they help. Haldane's statement implies that by sacrificing himself for either two siblings (who share 50% of his genes) or eight cousins (who share 12.5% of his genes), he would effectively preserve 100% of his genetic contribution, demonstrating the principle of kin selection and inclusive fitness.

Step-by-step solution

Introduction to J.B.S Haldane's remark

J.B.S. Haldane was a British biologist and one of the founders of population genetics. His remark about being willing to lay down his life to save two brothers or eight cousins is related to the concept of kin selection in evolutionary biology. This concept is based on the idea that organisms can increase their genetic representation in future generations by helping their relatives, who share some portion of their genes.

Understanding Kin Selection

Kin selection is an evolutionary strategy wherein individuals help their close relatives survive and reproduce. In doing so, they indirectly pass on their genes, increasing their genetic representation in the future generations. This strategy can explain why individuals may act altruistically (i.e., selflessly) towards their relatives, as helping relatives increases the chances of their shared genes being passed on.

Inclusive Fitness

Inclusive fitness is a measure that combines an individual's direct fitness (the number of offspring produced) with the indirect fitness (the number of offspring produced by the relatives it helps). This concept is essential for understanding kin selection, as it reveals that an individual's total genetic contribution to future generations also includes the genes of the relatives it helps.

Haldane's remark and its relation to Kin Selection and Inclusive Fitness

Haldane's statement about being willing to lay down his life to save two brothers or eight cousins implies that the genetic representation he would save by doing so would be equal to or greater than his contribution. Siblings share approximately 50% of their genes, while first cousins share approximately 12.5% of their genes. If Haldane sacrifices himself for two brothers, he would save two individuals with whom he shares 50% of his genes, effectively preserving 100% of his genetic contribution. Similarly, if he sacrifices himself for eight cousins, he would save eight individuals with whom he shares 12.5% of his genes, effectively preserving the same 100% of his genetic contribution (8 cousins * 12.5% = 100%). This idea illustrates the principle of kin selection and inclusive fitness, where an individual's actions can favor their genetic representation in future generations by helping their relatives, who share a portion of their genes. Haldane's remark is a succinct example of how this concept can work in practice.

Key concepts

J.B.S. Haldane

J.B.S. Haldane was a pioneering figure in the field of evolutionary biology and made significant contributions to population genetics. Known for his sharp wit and profound insights, Haldane had a unique ability to communicate complex scientific ideas in an accessible manner. One of his most famous quips relates to kin selection, a concept he helped develop, which illustrates the evolutionary benefit of helping relatives. His hypothetical willingness to sacrifice himself for the survival of his brothers or cousins highlights the importance of genetic relatedness in evolution. This intuitive explanation serves as an entry point for students to explore the deeper implications of genetic inheritance and altruistic behavior in the natural world.

Evolutionary Biology

Evolutionary biology examines how life on Earth has changed and diversified over time through a process known as natural selection. The key idea here is that organisms with traits that provide a survival or reproductive advantage are more likely to pass on these characteristics to the next generation. Kin selection is a cornerstone of this field, offering a way to understand why certain seemingly selfless behaviors persist. By embracing this concept, students can appreciate how evolution shapes not just physical traits but also behaviors, especially those related to social interactions and family dynamics.

Inclusive Fitness

The concept of inclusive fitness, formulated by biologist W.D. Hamilton, extends the idea of an organism's success beyond merely producing offspring—direct fitness—to also consider the reproductive success of that organism's relatives—indirect fitness. This notion reconciles the existence of altruism in nature with the principle of survival of the fittest; an individual can ensure the propagation of its genes by aiding relatives. Simplifying this concept for students, inclusive fitness can be thought of as a cumulative measure of an organism's genetic influence on the next generation, both through its own offspring and through the support of kin.

Population Genetics

Population genetics is a subfield of genetics that focuses on the genetic makeup of populations rather than individuals. It studies how allele frequencies in a population change over time owing to various factors such as mutation, selection, genetic drift, and gene flow. J.B.S. Haldane's work laid the foundation for this field by providing mathematical models for these complex processes. When discussing population genetics with students, it is crucial to emphasize that the genetic composition of a population is dynamic and influenced by both its members' reproductive success and their interactions, underlining the interconnectedness between genetics and behavior.

Altruism in Animals

Altruism in animals, a behavior that benefits others at a cost to oneself, has perplexed scientists for decades. In the animal kingdom, such acts are not just random kindness but can be explained by kin selection. Animals, including humans, may evolve to act in ways that favor the reproductive success of their relatives, even if it means sacrificing their own. For students, understanding that this altruistic behavior can be influenced by the degree of genetic relatedness offers a logical explanation for why we see animals—ranging from social insects to large mammals—performing selfless acts for the benefit of their kin.

Occasionally, we observe altruism towards non-relatives which can be explained by the benefits of reciprocity or societal structure. However, when breaking down these behaviors, the driving force of genetic survival is central, providing a compelling explanation for the altruistic acts observed in the natural world.