natural selection

• Natural selection is the process by which the organisms that are best adapted in a particular environment are most likely to survive and reproduce, passing on their advantageous alleles to their offspring
• Genotype is the genetic make-up of an organism with respect to a particular feature
• Phenotypes are the physical traits (including biochemical characteristics) expressed as a result of the interactions of the genotype with the environment
• An allele is a version of a gene, a variant
• Ecology is the study of the interactions of organisms with each other and with the environment in which they live
• A niche is the role of an organism within the habitat in which it lives
• An anatomical adaptation is an adaptation involving the form and structure of an organism
• A physiological adaptation is an adaptation involving the way the body of the organism works, including differences in biochemical pathways or enzymes
• A behavioural adaptation is an adaptation involving programmed or instinctive behaviour making organisms better adapted for survival
• Selection pressure is the pressure exerted by a changed environment or niche on individuals in a population, causing changes in the population as a result of natural selection
• Industrial melanism is the evolution of dark-coloured individuals in a habitat that has been made darker by industrial pollution, e.g. soot
• Directional selection is natural selection showing a change from one dominant phenotype to another in response to a change in the environment - one phenotype is selected for over all the others
• A gene pool is all of the alleles of all of the genes in a population
• Speciation is the formation of a new species
• Hybridisation is the production of offspring as a result of sexual reproduction between individuals from two different species
• Geographical isolation occurs when a physical barrier such as a river or a mountain range separates individuals from an original population
• Ecological isolation occurs when two populations inhabit the same region, but develop preferences for different parts of the habitat
• Seasonal isolation occurs when the timing of flowering or sexual receptiveness in some parts of a population drifts away from the norm for the group, leading to groups reproducing several months apart
• Behavioural isolation happens when changes occur in the courtship ritual, display or mating pattern so that some animals do not recognise others as potential mates, possibly due to mutations changing colour or pattern of markings
• Mechanical isolation happens when mutations change the genitalia of animals, making successful mating only possible with some members of the group, or changing the relationship between stigma and stamens in flowers, leading to unsuccessful pollination between some individuals
• Allopatric speciation is speciation that occurs when populations are physically or geographically separated, with no interbreeding or gene flow between the populations
• An endemic species is a species that evolves in geographical isolation and is found in only one place
• Adaptive radiation is a process by which one species evolves rapidly to form a number of different species that all fill different ecological niches
• Marsupials are mammals that give birth to very immature young and then protect them in pouches
• Monotremes are primitive mammals that lay eggs and feed their offspring with milk from mammary glands
• Placental mammals are mammals that provide for the developing fetus during gestation through a placenta
• Sympatric speciation is speciation that takes place between populations of a species living in the same place

  • Populations become reproductively isolated by mechanical, behavioural or seasonal mechanisms
  • Gene flow continues between the populations to some extent as speciation takes place