Researchers Highlight Challenges in Measuring Biological Fitness Despite Its Importance

Biological fitness, a concept that links ecological and evolutionary thought, remains challenging to define and accurately measure due to the spatial and temporal heterogeneity in abiotic and biotic environments, according to a recent review by researchers. The study, which examines the definitions and approaches to measuring fitness at various levels, emphasizes the importance of understanding the mechanisms underlying fitness and its relationship with adaptation.

The researchers investigate the fundamental theorem of natural selection (FTNS) proposed by R.A. Fisher, which states that the rate of change in a population's average fitness equals the additive genetic variance in fitness at that time. However, the FTNS has been a subject of debate, with some arguing it is useless while others contend it is a general theorem.

The review also discusses a paper by two creationists, Bill Basener and John Sanford, who aimed to show that the FTNS offers mathematical proof of Darwinian evolution and that it is incomplete because it does not consider the effects of new mutations on fitness. In response, other researchers aimed to clarify the assumptions of the FTNS and demonstrate that it is a general theorem.

Why this matters: Understanding biological fitness is essential for bridging the gap between ecological and evolutionary perspectives. However, the complexity of biological systems and the influence of environmental factors on fitness pose significant challenges in achieving a comprehensive understanding of this concept.

The study explores the antagonistic pleiotropy hypothesis, which suggests that a single gene can have both beneficial and detrimental effects on an organism's fitness. This hypothesis provides a partial explanation for the evolutionary theory of aging, as natural selection tends to favor alleles with early beneficial effects but later deleterious effects. The researchers also provide examples of genetic trade-offs between different fitness components, such as the trade-off between larval survival and adult size in fruit flies, and the trade-off between days to flower and reproductive capacity in annual plants.

The review highlights the role of antagonistic pleiotropy in the survival of genetic disorders, such as sickle cell anemia, which can be maintained at medically relevant frequencies due to minor beneficial pleiotropic effects, despite their severe deleterious health impacts. The researchers emphasize the need for a comprehensive understanding of fitness to bridge the gap between ecological and evolutionary perspectives, despite the challenges posed by the complexity of biological systems and the influence of environmental factors on fitness.

Key Takeaways

• Biological fitness is challenging to define and measure due to environmental heterogeneity.
• The fundamental theorem of natural selection remains debated, with differing views on its utility.
• Antagonistic pleiotropy hypothesis explains how a gene can have both beneficial and detrimental effects.
• Genetic trade-offs exist between fitness components, like larval survival and adult size.
• Comprehensive understanding of fitness is needed to bridge ecology and evolution, despite challenges.