Quick questions on Evolution by natural selection (Darwin, Wallace, fitness, adaptation): VCE Biology Unit 4

Charles Darwin (1809-1882) developed his ideas during the voyage of HMS Beagle (1831-1836), particularly from observations of finches and tortoises in the Galapagos Islands. He proposed that species change over time through descent with modification, driven by natural selection. He delayed publication for over twenty years while gathering evidence.

Natural selection occurs whenever four conditions are met:

A selection pressure is any factor that causes differential survival or reproduction. Common examples include:

Fitness is the relative reproductive success of an individual or genotype: how many viable, fertile offspring it leaves compared with others. It is measured by descendants, not by strength or longevity.

An adaptation is a heritable trait that increases an organism's fitness in its environment. Adaptations can be:

Evolution at the population level is measured by a change in allele frequency in the gene pool. If the allele for grey beetle colour rises from 30 per cent to 80 per cent of the population over twenty generations, the population has evolved.

Although natural selection is the focus, three other mechanisms also change allele frequency:

Individuals do not evolve. Populations evolve. An individual cannot change its alleles after birth.

Selection is not goal-directed. Variation already exists; the environment then favours some variants over others.

Fitness is reproductive success, not physical fitness. A weak individual that leaves many offspring has higher fitness than a strong one that leaves few.

Mutation provides variation. Natural selection acts on that variation. Both are needed.

A tan from sunbathing is variation, but it is not heritable, so natural selection cannot act on it.