7.3.5 Evolution

Key Processes in Evolution

1. Genetic Variation:

• Variation arises from mutations, meiosis, and random fertilisation of gametes.
• These processes ensure a variety of alleles within a population.

2. Selection Pressures:

• Environmental factors, such as predation, competition, or disease, act as selection pressures.
• These determine which individuals are most likely to survive and reproduce.

3. Differential Survival and Reproduction:

• Individuals with advantageous alleles are more likely to survive, reproduce, and pass these alleles to their offspring.
• Over time, the frequency of these advantageous alleles increases in the population.

4. Adaptation:

• Populations evolve to become better adapted to their environment through the accumulation of advantageous alleles.

Types of Evolution

1. Divergent Evolution:

• Populations of the same species evolve to become different due to different selection pressures in varying environments.
• Leads to the formation of new species (speciation).

2. Convergent Evolution:

• Unrelated species evolve similar adaptations due to similar selection pressures in the same type of environment.

Evidence for Evolution

1. Fossil Record:

• Shows how species have changed over millions of years.
• Provides links between extinct and modern species.

2. Molecular Evidence:

• Similarities in DNA sequences, amino acid sequences, and protein structures suggest common ancestry.

3. Homologous Structures:

• Structures with similar anatomy but adapted for different purposes (e.g., the pentadactyl limb).