Biologinen evoluutio

Biological Evolution

• Evolution is the change in the heritable characteristics of biological populations over successive generations.
• This change is observed by the changes in allele frequencies within a population.
• The processes driving evolution include natural selection, genetic drift, gene flow, and mutations.
• Evolution is supported by numerous lines of evidence including fossil records, comparative anatomy, comparative embryology, biogeography, and molecular biology.

Mechanisms of Evolution

• Natural Selection: Individuals with heritable traits better suited to their environment are more likely to survive and reproduce, passing on these advantageous traits to their offspring.
• Genetic Drift: Random fluctuations in allele frequencies, especially prominent in small populations. This can lead to the loss or fixation of alleles regardless of their adaptive value.
• Gene Flow: The movement of genes between populations, altering allele frequencies and potentially preventing divergence.
• Mutations: Changes in the DNA sequence that introduce new alleles into a population. Mutations are the ultimate source of genetic variation and can be harmful, neutral, or beneficial.

Evidence for Evolution

• Fossil Record: Preserved remains or traces of past organisms demonstrate a history of life on Earth, with a progression from simpler to more complex forms. Fossils reveal evolutionary sequences, transitional forms, and extinction events.
• Comparative Anatomy: Similarities in anatomical structures (homologous structures) among different species suggest a shared ancestry. Vestigial structures, remnants of formerly functional anatomical features, also provide evidence of evolutionary relationships.
• Comparative Embryology: Early stages of development in different species exhibit remarkable similarities, pointing to a common evolutionary history.
• Biogeography: The global distribution of species supports the concept of common ancestry and diversification.
• Molecular Biology: Comparing DNA and protein sequences across organisms reveals evolutionary relationships. The more closely related two species, the more similar their genetic material.

Modes of Natural Selection

• Directional Selection: Favors individuals at one extreme of a phenotypic trait, for example, an increase in beak size in a bird population over time.
• Stabilizing Selection: Favors intermediate phenotypes, reducing variation around the mean.
• Disruptive Selection: Favors individuals at both extremes of a phenotypic range, potentially leading to the formation of multiple distinct forms.

Speciation

• Speciation is the process by which new species arise.
• Allopatric speciation occurs when populations are geographically isolated, leading to the evolution of reproductive isolation.
• Sympatric speciation occurs when new species form within the same geographic area, often through mechanisms like polyploidy.

Adaptation

• Adaptations are traits that enhance an organism's survival and reproduction in a specific environment.
• Natural selection drives the evolution of adaptations, giving organisms with advantageous traits a greater chance of survival and reproduction.
• Adaptations can be structural, physiological, or behavioral.

Phylogeny

• Phylogeny is the evolutionary history of a group of organisms.
• Phylogenetic trees are diagrams illustrating evolutionary relationships, showing common ancestors and branching patterns of lineages.

Abiotic factors

• Environmental factors like temperature, sunlight, water availability, and soil composition significantly impact the evolution of organisms.
• These factors influence individual survival and reproduction, driving adaptation.

Coevolution

• Coevolution describes reciprocal evolutionary change between interacting species.
• This can occur between predator and prey, or between parasite and host.
• Interactions between species can drive the evolution of traits enhancing the interaction.