Evolution History and Mechanisms

Evolution History

Darwin's Voyage on the Beagle

• Charles Darwin embarked on a voyage on the HMS Beagle in the 1830s, which was instrumental in shaping his ideas about natural selection and evolution.
• Observations made during this journey, such as variations among species on the Galápagos Islands, led him to question why so many species existed and how they came to be.

Influences on Darwin

• Darwin was influenced by earlier thinkers, including Lamarck who proposed early ideas about evolution, and Malthus whose writings on population growth underscored competition for resources.

Evidence for Evolution

• A variety of evidence supports the theory of evolution, including:
  • Fossil records showing gradual changes in species over time.
  • The study of homology, or similarities in structure between different species, indicating common ancestry.
  • Biogeography, which examines the distribution of species across geographical areas.

Hypothesized Mechanism: Natural Selection

• Natural selection is a key mechanism proposed by Darwin to explain how evolution occurs:
  • Variation: Individuals in a population exhibit variations in traits.
  • Competition: Individuals compete for limited resources (like food and mates).
  • Reproduction: Those with favorable traits are more likely to survive and reproduce, passing on those traits to the next generation.

Sexual Selection

• Sexual selection is a form of natural selection where individuals with certain traits are more successful at attracting mates.
• This can lead to pronounced differences between males and females in a species (sexual dimorphism).
• Examples include brighter plumage in male birds to attract females.

Modern Evolutionary Biology

Population Genetics

• Population genetics studies the genetic composition of populations and how it changes over time, emphasizing the role of alleles and gene frequencies.

Testing for Evolution

• Scientists use various methods to test whether evolution is occurring in a population, including:
  • Monitoring changes in allele frequency over generations.
  • Identifying selective pressures within environments.

Evolutionary Mechanisms

Selection

• Selection occurs when certain traits confer advantages in survival or reproduction, leading to an increase in those traits in the population over time.

Genetic Drift

• Genetic drift refers to random changes in the frequency of alleles in a population, particularly in small populations.
• This can lead to significant evolutionary changes over time, independent of natural selection.

Gene Flow

• Gene flow (or gene migration) is the transfer of genetic material between populations, which can introduce new alleles and affect population diversity.

Mutation

• Mutations are changes in DNA that can introduce new traits into a population. They are a source of genetic variation essential for evolution.

Inbreeding

• Inbreeding refers to the reproduction between closely related individuals, which can lead to a decrease in genetic diversity and an increase in the likelihood of genetic disorders.
• This can negatively impact population genetics, making populations more vulnerable to environmental changes.