Natural Selection and Speciation

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Study Notes

Natural Selection

Natural selection is the process where organisms better adapted to their environment tend to survive and produce more offspring.
This leads to changes in the genetic makeup of a population over time.
Key factors driving natural selection include:
- Variation in traits within a population.
- Inheritance of these traits.
- Differential survival and reproduction based on these traits.
Natural selection acts on existing variations within a population; it does not create new traits.
Selective pressures can be environmental factors like:
- Predation
- Competition for resources
- Climate change
Examples of adaptations due to natural selection:
- Camouflage in animals
- Antibiotic resistance in bacteria
- Beak shape variations in finches

Speciation

Speciation is the evolutionary process by which new biological species arise.
There are several mechanisms of speciation:
- Allopatric speciation: occurs when a population is geographically isolated, leading to genetic divergence due to different selective pressures.
- Sympatric speciation: occurs when a new species arises within the same geographic area, often due to factors such as:
  - Polyploidy (extra sets of chromosomes)
  - Sexual selection
  - Habitat differentiation
Key factors in speciation:
- Reproductive isolation: the inability of different species to interbreed and produce fertile offspring.
- Genetic divergence: differences in gene pools between populations.
- Geographic isolation or ecological factors
Speciation is a gradual process, taking millions of years.

Mutation and Genetic Drift

Mutations are random changes in the DNA sequence.
Mutations can be beneficial, neutral, or harmful, affecting traits.
Mutations are a source of new genetic variations in a population.
Genetic drift is a random change in allele frequencies within a population, particularly evident in small populations.
Genetic drift can lead to the loss or fixation of alleles, regardless of their adaptive value.
Two key types of genetic drift are:
- Bottleneck effect: drastic reduction in population size due to events like natural disasters. This results in a loss of genetic diversity.
- Founder effect: when a small group of individuals establishes a new population in a new area, potentially carrying alleles that are different from the original population.

Evidence of Evolution

Fossil records provide evidence of past life forms and show the evolutionary history of organisms.
Fossil succession: fossils appear in a specific order in the rock layers.
Comparative anatomy: the study of similarities and differences in the anatomy of different species shows common ancestry.
- Homologous structures: similar structures derived from a common ancestor, even if their function differs. (e.g., human arm, bat wing).
- Analogous structures: structures that have similar functions but are not derived from a common ancestor. (e.g., wing of a bird and wing of a butterfly).
Comparative embryology: comparison of the embryonic development of different species can reveal similarities and evolutionary relationships.
Molecular biology: comparisons of DNA and protein sequences provide powerful evidence of evolutionary relationships between species.
Biogeography: patterns of distribution of species across the globe reflect their evolutionary history.
The theory of evolution explains patterns of biodiversity, adaptations, and the unity of life.
Transitional fossils are a key component of supporting evolution.
Vestigial structures are structures in organisms that have lost most of their original function through evolution.

Description

This quiz explores the concepts of natural selection and speciation, focusing on how organisms adapt to their environment and how new species arise. It covers key factors, mechanisms, and examples of adaptations related to these processes. Test your understanding of evolutionary biology with this engaging quiz.