Biology: Evolution and Core Concepts

• Biology is the scientific study of life, examining structure, function, growth, origin, evolution, distribution, and taxonomy of living organisms.
• Evolution is the change in the heritable characteristics of biological populations over successive generations.
• Evolutionary processes give rise to diversity at every level of biological organization, including species, individual organisms, and molecules.

Core Concepts in Biology

• Cell theory posits the cell as the basic unit of life; all living organisms are composed of cells, and all cells arise from pre-existing cells.
• Genes are units of heredity made of DNA that provide instructions for building proteins and regulating cellular activities.
• Homeostasis is the ability of an organism to maintain a stable internal environment despite external changes.
• Evolution refers to the process by which populations of organisms change over time.

Basics of Evolution

• Evolution is driven by natural selection, mutation, genetic drift, and gene flow.
• Natural selection is the differential survival and reproduction of individuals due to differences in phenotype.
• Mutation involves a change in the DNA sequence of an organism.
• Genetic drift is the random change in the frequency of alleles in a population.
• Gene flow is the movement of genes between populations.

Evidence for Evolution

• Fossil record comprises preserved remains or traces of ancient organisms showing a historical sequence of life.
• Comparative anatomy studies similarities and differences in the anatomy of different species.
• Embryology studies the development of embryos, revealing similarities among diverse organisms.
• Molecular biology studies DNA and protein sequences to determine evolutionary relationships.
• Biogeography studies the geographic distribution of species.

Natural Selection

• Natural selection requires variation, inheritance, and differential reproductive success.
• Variation means individuals within a population exhibit differences in their traits.
• Inheritance signifies traits must be heritable, meaning they can be passed from parents to offspring.
• Differential reproductive success means individuals with certain traits are more likely to survive and reproduce than others.
• Adaptation is a trait that enhances the survival and reproduction of an organism in its environment.

Mechanisms of Evolution

• Mutation is a source of new genetic variation.
  • Point mutations include single base changes in DNA.
  • Chromosomal mutations involve large-scale changes in chromosome structure.
• Genetic drift involves random changes in allele frequencies.
  • Bottleneck effect is the reduction in population size due to a random event.
  • Founder effect is the establishment of a new population by a small number of individuals.
• Gene flow is the transfer of genes between populations, which can introduce new alleles and increase genetic variation.
• Non-random mating occurs when individuals choose mates based on specific traits.
  • Assortative mating means individuals with similar phenotypes mate more frequently.
  • Disassortative mating means individuals with dissimilar phenotypes mate more frequently.

Speciation

• Speciation is the process by which new species arise.
• Allopatric speciation happens when populations are geographically isolated, preventing gene flow.
• Sympatric speciation occurs when new species arise within the same geographic area.
• Reproductive isolation involves mechanisms that prevent different species from interbreeding.
  • Prezygotic barriers prevent the formation of a zygote.
  • Postzygotic barriers occur after the formation of a hybrid zygote.

Types of Evolution

• Microevolution comprises small-scale changes in allele frequencies within a population over a few generations.
• Macroevolution involves large-scale evolutionary changes, such as the origin of new species or major evolutionary trends.
• Adaptive radiation is rapid diversification of a lineage into many different forms, each adapted to a specific ecological niche.
• Convergent evolution involves independent evolution of similar traits in different lineages due to similar environmental pressures.
• Coevolution consists of reciprocal evolutionary adaptations between two interacting species.

Evolutionary History

• Phylogeny is the evolutionary history of a group of organisms, often represented as a phylogenetic tree.
• Systematics is the study of the diversity and evolutionary relationships of organisms.
• Taxonomy is the science of naming and classifying organisms.
• Cladistics is a method of classifying organisms based on shared derived characters.
• Molecular clock uses mutation rates in DNA to estimate the time of evolutionary events.