Lecture 4: Intro Natural Selection
o Developed by Darwin ; explains how evolution can occur
o The book: the origins of species by means of natural selection is devoted to
explaining this mechanism
o Natural Selection: differences in survival and reproduction of phenotypes leading
to differences in their contribution the next generation, resulting in a change in
frequency of heritable phenotypic variations in populations overtime
Components of Natural Selection:
o Living things produce more offspring than can be supported
o There is a constant struggle for existence.
o Individuals in a population vary in their phenotypes.
o Some of this variation is heritable (genotypes).
o Those individuals best adapted to current conditions are most likely to survive
and reproduce themselves
o If these adaptations are heritable, they will be passed on to their offspring.
o Natural selection acts on phenotypes, but only if there is a change in allele
frequencies (eg Gene Frequencies) in a population has evolution occurred.
o Population genetics is the study of allele and genotype frequencies and their
changes in entire populations.
Evolutionary Fitness ( Darwinian Fitness)
o The term ‘fitness’ refers to an individuals contribution to the next generation in
terms of number of offspring
o The more offspring an individual contributes to the next generation, the greater
the individuals evolutionary fitness
Measure of Fitness:
o Fitness is a measure of reproductive success, which is a