Natural selection: Driving force of evolution and biodiversity
Definition
Natural selection
Natural selection is the primary mechanism behind evolutionary change, shaping species over time and leading to the incredible biodiversity we see on Earth today.
- It operates continuously, acting on genetic variation within populations, favoring traits that improve survival and reproduction.
- Over millions to billions of years, this process has resulted in the diversity of life across different ecosystems.
- Think of natural selection as nature’s quality control system.
- Only the most well-adapted designs continue to be produced and refined over time.
Mechanism of Natural Selection
- Natural selection relies on four fundamental principles: variation, overproduction, competition, and differential survival.
- Together, these processes explain how populations evolve over time.
Darwin’s Finches
- In the Galápagos Islands, finches evolved different beak shapes suited for different food sources.
- Birds with stronger beaks survived better on hard seeds, passing this trait to their offspring.
- Over time, distinct species emerged, illustrating adaptive radiation driven by natural selection.
In questions about natural selection, always include:
variation → selection pressure → differential survival → inheritance → evolution.
1. Variation
Definition
Variation
Variation refers to the differences in traits among individuals of a population, resulting from genetic and environmental factors.
- Within every population, individuals vary in physical and behavioral traits due to genetic differences and mutations.
- These variations form the raw material for evolution.
- Genetic diversity arises through:
- Random mutations during DNA replication
- Sexual reproduction, which combines genetic material from two parents
- Gene flow, where genes move between populations through migration
In a rabbit population, genetic variation may produce fur colors ranging from white to dark brown.
2. Overproduction
- Most species produce more offspring than the environment can support.
- This creates competition for limited resources such as food, mates, and shelter.
- Only a fraction of offspring survive to adulthood.
- Those with advantageous traits are more likely to reach reproductive age.
A pair of fish may lay hundreds of eggs, but only a few survive to adulthood because of predation and competition.
3. Competition and Struggle for Survival
- When resources such as food, water, or shelter are scarce, individuals compete for survival.
- This “struggle for existence” determines which individuals are best adapted to current environmental conditions.
- Selection pressures, such as predation, disease, and climate, favor some individuals over others.
- Lions compete for territory and mates.
- Only dominant males reproduce, passing on their strong, adaptive genes.
4. Differential Survival and Reproduction
- Individuals with advantageous traits, those that improve survival or reproduction, are more likely to survive and pass on those traits to their offspring.
- Over generations, the frequency of these beneficial alleles increases in the population.
