biology 2/18
Impact of Environment on Cognitive Functions
- Various external factors can affect cognitive functions, such as:
- Cognitive function variation is not solely inherited.
Cerebral Palsy Example
- Cerebral Palsy Definition:
- Generally not inherited but caused by fetal distress leading to brain development issues due to oxygen deprivation during gestation or childbirth.
- Conclusion: Not all variation in traits is genetic.
Natural Selection and Evolutionary Forces
- Emphasizes that:
- Natural selection is one of several mechanisms of evolution.
- Other evolutionary forces include:
- Mutation
- Genetic drift
- Gene flow
Darwin's Contribution to Natural Selection
- Charles Darwin is well-known for his assertion that natural selection is a primary force driving evolutionary change.
- However, evolutionary changes can occur through mechanisms other than natural selection.
Microevolutionary Change
- Defined as:
- Changes in allele frequencies from generation to generation.
- Forces of evolution can be any factors that influence allele frequencies in a population over time.
Forces of Evolution
- Major evolutionary mechanisms include:
- Natural selection
- Sexual selection
- Genetic drift
- Mutation
- Gene flow
Natural Selection
- Misunderstood often as a singular process:
- It encompasses all forces causing some individuals to reproduce more successfully than others.
Sexual Selection
- Defined as:
- A type of natural selection related to an organism's ability to attract mates based on phenotypic traits.
- Important aspects include:
- Phenotypic Variation: Variation in traits that are inheritable.
- Attractiveness influences reproductive success.
- Examples:
- Male peacocks exhibit colorful plumage to attract females.
- Consequences:
- Sexual selection may lead to traits that could hinder survival (e.g., peacock's tail).
Genetic Drift
- Definition:
- Random changes in allele frequencies often associated with smaller populations.
- Important notes:
- Genetic drift occurs randomly and can happen whether populations are large or small, but its effects are more dramatic in small populations.
- Example:
- In an extended family, variations in reproduction rates may not correspond to fitness but random chance.
- Analogy:
- Predicting election outcomes based on a biased sample of voters illustrates how small samples can lead to skewed allele frequency assessments.
Gene Flow
- Defined as:
- The transfer of alleles between populations through migration.
- It allows for genetic variation within populations as alleles are exchanged, thus potentially introducing new traits.
Mechanisms Causing Allele Frequency Change
- The main mechanisms include:
- Natural selection
- Sexual selection
- Mutation
- Genetic drift
- Gene flow
Direct Observation of Evolution
- Example from the Galapagos Islands:
- 1976 study measured finch beak depth.
- Average beak depth before drought: approximately 9 mm.
- Impact of 1977 drought:
- Many birds starved due to lack of available food (small seeds).
- Surviving birds had larger beaks suitable for larger seeds.
- Post-drought beak measurements revealed an increase to approximately 10.5 mm.
Generational Change
- This change occurred over just one generation, showcasing microevolution.
- Evolutionary Mechanism:
- The allele frequencies shifted as alleles coding for larger beak depth became more prevalent due to natural selection.
Long-term Beak Depth Variation
- The study continued to monitor beak depths, noting fluctuations over years correlating to environmental conditions (drought/rain).
Conclusion on Evolution
- Emphasizes:
- No single trait evolves in isolation; numerous traits are affected by multiple environmental pressures simultaneously.
Final Notes
- Understanding these evolutionary mechanisms is critical as they influence biological diversity and adaptation strategies in various populations.
- Persistence of genetic variations continues to showcase the dynamic nature of evolution based on environmental contexts.