What Drives The Speed Of Evolution?

The speed of evolution can be defined as the number of generations required for an initially random population to reach a specific evolutionary target or adapt to a defined goal. There are a number of factors that affect the speed of evolution, and many do not act in isolation. New research suggests that the speed of evolution is actually taking place up to four times faster than previously thought.

Genetic Variation

Mutation rates, gene flow and sexual reproduction are just some of the genetic factors that affect the speed of evolution. Mutations are often key to introducing new genetic variations that lead to different organism traits. If these traits prove to be advantageous, natural selection can help those organisms to proliferate. Gene flow – the exchange of genetic material between diverse populations, often facilitated by migration and reproduction – further increases adaption to changing environments.

An example can be seen in the peppered moth, which exists in both light and dark colours due to a genetic mutation. During the Industrial Revolution, increased pollution darkened the trees in surrounding areas, giving a distinct advantage to the dark-coloured moths with the mutation, which then became more common in the population.

Population Size

Small populations, which can result from environmental constraints or natural disasters, are often subject to evolutionary disadvantages. Genetic drift – a concept where genetic material is passed on by chance as opposed to natural selection – plays a larger role in smaller populations. Harmful materials are also more likely to be passed on through inbreeding, however, with smaller groups more likely to experience faster evolutionary changes.

Around 10,000 years ago, cheetahs experienced a population bottleneck which reduced their genetic diversity and gave rise to genetic drift. Today, cheetahs experience low genetic diversity, which have given rise to genetic defects and reduced fertility.

In larger populations, genetic drift plays a less significant function, as natural selection takes on a more dominant role. Larger populations tend to act as a larger repository of genetic diversity, which can enhance adaptability, although the rate of evolution is far slower due to greater genetic dilution.

Environmental Factors

Environmental factors play a key role in the rate of evolution. Stable environments tend to result in slower rates of evolution due to less pressure to adapt, while fluctuating environments often drive rapid change in order to promote survival. Crocodiles have existed for over 200 millions years but have physically remained largely unchanged. Small changes in their river environments, temperature and food availability have led to a fairly consistence genetic diversity.

Coevolution is another key factor, often observed in predator-prey dynamics. In these interactions, evolutionary “arms races” occur, with each species rapidly evolving in response to the other. Additionally, human intervention has artificially accelerated evolutionary traits through selective breeding.