Biology (university) · Part 08
Evolution and diversity of life
How populations change over generations, how new species form, and how life is classified.
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- Natural selectionIndividuals in a population vary, some of that variation is inherited, and individuals with helpful traits leave more offspring. Over generations those traits become more common.
- FitnessHow many offspring an individual leaves that survive to reproduce, compared with others. Fitness is about reproductive success, not strength. An adaptation is a trait that raises fitness in a given environment.
- Genetic driftRandom changes in allele frequencies from one generation to the next, caused by chance. The effect is strongest in small populations. Bottlenecks and founder effects are examples.
- Gene flowThe movement of alleles between populations when individuals or gametes move. It makes populations more similar and adds new variation.
- Hardy-Weinberg equilibriumA model for a population that is not evolving. Allele frequencies stay constant if there is no selection, mutation, drift or gene flow, and mating is random. If p and q are the two allele frequencies, p + q = 1 and genotype frequencies are p^2 + 2pq + q^2 = 1.
- SpeciationThe formation of new species. In allopatric speciation, a physical barrier splits a population and the groups evolve apart. In sympatric speciation, new species form in the same area. Reproductive isolation keeps them separate.
- Evidence for evolutionSeveral independent lines point to common ancestry: fossils, homologous structures (the same bones used differently), DNA and protein similarity, and observed evolution such as antibiotic resistance.
- Phylogenetic treeA branching diagram showing evolutionary relationships. Each branching point is a common ancestor. Species closer together on the tree share a more recent ancestor.