Natural Selection and the Concept of Fitness

Introduction

Natural selection is the processes by which organisms with traits that provide survival and reproductive advantages pass those traits to the next generation. It is the main driving force behind evolution.

The concept of fitness is central to natural selection and refers to the ability of an organism to survive and reproduce in a given environment.

Principles of Natural Selection

1. Variation – Individuals in a population exhibit genetic differences.
2. Heritability – Traits are passed from parents to offspring.
3. Differential Survival and Reproduction – Some traits increase an organism’s likelihood of survival and reproduction.
4. Adaptation – Over generations, beneficial traits become more common in the population.

Concept of Fitness

1. Fitness is measured by an organism’s reproductive success.
2. Higher fitness means more offspring contribute to the gene pool.
3. Survival alone is not enough; reproduction is key.

Types of Fitness

1.      Absolute Fitness (W): Total number of offspring an individual produces.

2.      Relative Fitness (w): Compares the reproductive success of different genotypes.

w=Reproductive output of genotype

Reproductive output of most fit genotype

w = \frac{\text{Reproductive output of genotype}}{\text{Reproductive output of most fit genotype}}

3.      Inclusive Fitness: Considers both direct fitness (personal reproduction) and indirect fitness (helping relatives pass genes).

Examples of Natural Selection and Fitness

1.      Industrial Melanism in Peppered Moths: Dark-colored (melanic) moths increased in polluted areas due to higher survival (higher fitness). Light-colored moths were more visible to predators and decreased.

2.      Antibiotic Resistance in Bacteria: Bacteria with resistance genes survive antibiotics and reproduce. Over time, the resistant population dominates.

3.      Darwin’s Finches (Beak Adaptations):  Different beak sizes evolved based on food availability. Birds with suitable beaks had higher survival and reproductive rates.

Importance of Natural Selection and Fitness

1. Explains evolutionary changes over time.
2. Determines species survival in changing environments.
3. Influences biodiversity and ecological interactions.

 

References

1. Darwin, C. (1859). On the Origin of Species. John Murray.
2. Futuyma, D. J. (2013). Evolution (3rd ed.). Sinauer Associates.
3. Hallam, A. (1992). Phanerozoic Sea-Level Changes. Columbia University Press.
4. Mayr, E. (2001). What Evolution Is. Basic Books.
5. Stanley, S. M. (1987). Extinction. Scientific American Library.