Understanding Evolution: Key Concepts and Examples
A Biologist’s Perspective on Evolution
Evolution is a theory supported by a vast amount of evidence. A classic example is Darwin’s finches.
Understanding Convergent Evolution
Convergent evolution occurs when two species in different areas evolve similarities due to natural selection acting on those characteristics.
Genetics and Evolution
Genes and Loci
A gene is represented by its alleles. A locus can be polymorphic.
Genetic Drift
A restriction in genetic variability caused by a drastic reduction in population size is known as the bottleneck effect.
Radioactive Isotopes and Dating
A rock containing a radioactive isotope with a half-life of 4,200 years is 12,600 years old (3 half-lives). A technique used to date fossils is radioactive isotope dating.
Isolating Mechanisms
Prezygotic and Postzygotic Isolation
Types of isolating mechanisms include postzygotic and prezygotic isolation.
Reproductive Isolation
In a virgin pine forest divided by a canyon, the two squirrel populations become reproductively isolated.
Genetic Variation and Adaptation
Adaptive Radiation
Adaptive radiation is the existence of groups of closely related species recently evolved from a common ancestor, leading to a species cluster.
Founder Effect
After a coastal population is decimated by a storm, the remaining individuals exhibit the founder effect.
Hybrid Sterility
Hybrid sterility is a type of postzygotic isolating mechanism.
Disruptive Selection
When both extremes of an array of phenotypes are favored, it is called disruptive selection.
Founder Effect and Genetic Variation
Certain small populations exhibit the founder effect.
Darwin’s Theory of Evolution
Evidence for Evolution
Charles Darwin argued that evidence exists to support evolution. Cheetahs have little genetic variation due to a past bottleneck. Coloration in a certain species of birds is determined by a single gene with two alleles.
Domestication and Phenotypic Variation
Considerable phenotypic variation exists in many domesticated varieties. Darwin concluded that the beaks of Galapagos finches evolved due to natural selection. Darwin proposed that natural selection favors adaptive traits.
Natural Selection
Differential success in reproduction is known as natural selection. Diversity typically recovers within about ten million years and has increased since the beginning of life. There were more families of organisms during the Tertiary than the Cambrian period.
Domestication and Artificial Selection
Domestication of animals often leads to a variety of phenotypes. Due to character displacement, two closely related species may be sympatric.
Evidence and Mechanisms of Evolution
Analogous Structures
Evidence for evolution includes analogous structures. Evolution is said to violate the second law of thermodynamics because Earth is not a closed system.
Adaptations
Features that increase the likelihood of survival and reproduction are called adaptations.
Gene Flow and Hybridization
Gene flow can occur through hybridization.
Hardy-Weinberg Equilibrium
Hardy-Weinberg equilibrium assumes no polymorphic loci.
Speciation
Sympatric and Allopatric Speciation
If a new species arises due to polyploidy, it is considered sympatric speciation via allopolyploidy. If populations within the same area split into species, it is called sympatric speciation.
Genetic Drift and Speciation
In small populations, genetic drift can play a significant role in speciation.
Assortative and Disassortative Mating
In some populations, disassortative mating can occur.
Vestigial Structures
The side toes of a horse are considered vestigial structures.
Heterozygote Advantage
The text discusses the concept of heterozygote advantage.
Homologous Structures
Structures that have different appearances and functions but seem to have evolved from the same body part in a common ancestor are called homologous structures.
Conclusion
This comprehensive overview provides a deeper understanding of evolution, its mechanisms, and its impact on the diversity of life.