This essay will discuss the various factors which influence the rate of evolution. It will focus on evolution as define as how living organisms develop genetically inherited traits, rather than the more general “gradual development of something”. As such we will not be discussing cultural evolution within human populations or adaptive behaviours. Mutation is the key influencer of the rate of evolution. Mutation rate varies between species and even within different cell types in one species due to a variation in how accurate the DNA repair mechanism for error during replication is.
For example, human mitochondrial DNA mutates at a rate 1000 times faster than the genome. This influences the rate of evolution, as mutations provide variations which could go to fixation (i.e. becomes the baseline for further mutation) in the population. Without mutation, there is no variation in a population so no evolution at all, all of life would be the same.The strength of selection on an allele influences the rate of evolution. The stronger the selective pressure, the faster the evolution.
This is because it causes less fit alleles to be removed from the population faster as the fitter allele is passed on more often. This is because those with that allele are more likely to produce offspring (as they are more likely to survive that long or get more mates), thus the allele is more likely to be passed on to spread it across the entire population.The selective pressure on an allele may vary within a species between populations. This is because the ecosystem produces different selective pressures. Interactions between different species place different selective pressures and produce new niches.
This can be competitive or co-operative relationships.Competitive relationships come in the form of ‘arms races’, where there is an evolutionary form of one-up-man-ship where you must keep improving just to keep the same level fitness due to the improvement or those around you. These come in two forms: symmetrical where they are competing over same resources which can be intra or interspecies (though intraspecies does not compete for mates), and asymmetrical or antagonistic co-evolution where one species is causing harm to the other (e.g. predator-prey) with one evolving traits to avoid harm while the other evolves to keep up.
This can either be unilateral, e.g. speed, or ??, e.
g. camouflage and better eyesight.Co-operative relationships are mutually beneficial. These can form or between species in symbiosis (e.g. clown fish evolve to be immune to an anemone ??), or within species causing the faster evolution of behavioural traits (due to greater selective pressure as the individuals interact more) and intelligence to allow for better adaptive behaviour.
In humans, however, certain technological leaps due to our intelligence have slowed traditional evolution. For example, treatments for disease has slowed the evolution away from disease-causing alleles, and cross-continental travel has prevented speciation, causing us to form one large population). However, it has slowed not stopped, e.g. certain populations have evolved to have a higher frequency of the allele for sickle cell anaemia as though it is deadly in the homozygous form, it affords a heterozygous carrier protection against malaria. Humans also influence the rate of evolution of other species by applying selective pressure that would not occur naturally in the ecosystem. Artificial selection influences the rate and direction of evolution by breeding for traits that would not naturally be selected e.
g. a pug’s flat face. The rate of this evolution depends on humans. For example, humans domesticated wild dogs 12,000 years ago, but then dogs stayed pretty much the same until 150 years ago when people started breeding them for different traits so that today we have breeds that are so different you would think them different species. Humans also apply new selective pressures without meaning to, where animals must evolve to survive us. This is not the same kind of arms race as between other species as we aren’t evolving to match their changes, but they are evolving to try and survive us, e.g. hedgehogs evolving to not curl into balls to avoid danger due to traffic killing them.
A more stable environment will reduce the rate of evolution as there are fewer changes to the selective pressure, so once a species has optimised a trait as much as biomechanism and trade off?? Will allow it won’t change much. A more stable environment also reduces the likelihood a large portion of the population being wiped out causing a big change in allele frequency due to random sampling (Bottle-neck Effect).The route to better fitness effects the rate of evolution. If to evolve a fitter trait, you have to go through a stage where the trait is less beneficial it will slow evolution as it is more likely the population will stick with the current adaptation as evolution is blind and cannot see the future benefits. Thus if we visualise the adaptive landscape (with fitter adaptations at higher altitude, forming peaks at the fittest traits and troughs for less well-adapted traits), a population tends to evolve to the closest peak (local fitness maximum), rather than cross a trough to a different, higher peak (global fitness maximum. The existence of an alternative route between peaks meaning you don’t need to go via an adaptive trough increases the rate of evolution.
For example, Antirrhinum populations in different areas of Southern Europe evolved between two adaptive peaks of colour (yellow and magenta) by going through a transition phase with patterns of a mixture of the two colours rather than traversing the adaptive trough of being orange (which is less fit possibly due to being less attractive to pollinators) .The size of a population influences the rate of evolution. This is because smaller populations are more easily influenced by random sampling effects, influenced either by natural disaster or by the more common sampling effects of predation and mating. Thus, they have stronger genetic drift (which is the random change of allele frequency, making the frequency drift up or down). This also means that small populations can more easily transverse adaptive landscape troughs as the greater effect of random sampling may cause leaps around the adaptive landscape, putting the population closer to the global fitness maximum instead of the local.Large gene flow between populations (high immigration/ emigration rates) slow evolution due to an effectively larger population in a lot of mixing.
But smaller amounts allow a higher fitness allele to invade a population, to increase evolution rate in that population.When a species reproduces sexually rather than asexually it increases the rate of evolution as recombination events can produce more variation in traits and allows alleles to spread throughout the population rather than through only one lineage. Additionally, sexual reproduction influences the rate of evolution as sexual selection increases the rate of evolution as increases selective pressure to include not just fitness regarding the ability to survive but also in getting a mate.Sexual reproduction itself is a demonstration of how antagonistic co-evolutions influences the rate of evolution, as theoretically it’s greater fitness to pass on all your own genes, rather than only 50%. But the arms races against disease by avoiding the limited immunity of cloning makes sexual reproduction more favourable.
Evolution rate increases upon entering a new environment with previously unexploited niches (e.g. leaving the sea, the development of flight,) or recently vacated niches (e.g. asteroid 66 million years ago freeing up niches previously occupied by dinosaurs for mammals to fill).The size of an organism influences the rate of its evolution as smaller organisms reproduce faster and usually have more offspring.
This means there are more of the species so less likely to go extinct which puts an end to that evolution, and it is easier for smaller organisms to find new niches as they need to eat less food to survive, e.g. there are more niches for finches to fill than elephants.In conclusion, there are a vast many influences on the rate of evolution from the first mutations in single cell organisms to invention of car (from the increase in global warming affecting the selective pressure on every species on the planet to a individuals ability to avoid being roadkill).