Evolution

5.4.1 Define evolution.

Evolution is the cumulative change in the heritable characteristics of a population.

5.4.2 Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures.

Fossils, selective breeding and homologous structures have provided scientists with evidence that support the theory of evolution. As they started to study fossils they realised that these were not identical but had similarities with existing organisms. This suggested that organisms changed over time. Selective breeding of domesticated animals also provides this evidence as the domestic breeds have similar characteristics to the wild ones and can still breed with them. As selected wild individuals with desirable characteristics were bred, over time this resulted in a more desirable species from a human point of view. An example of this is the taming of wild wolves and their selective breeding in order to produce the domestic dogs we know today. This suggests that not only have these animals evolved but also that they can evolve rapidly. Finally scientists have found a number of homologous structures within different species. Many bones in the limbs are common to a number of species and therefore suggests that these have evolved from one common ancestor.

5.4.3 State that populations tend to produce more offspring than the environment can support.

Populations tend to produce more offspring than the environment can support.

5.4.4 Explain that the consequence of the potential overproduction of offspring is a struggle for survival.

If the mortality rate remains lower than the natality rate then a population will keep growing. As more offspring are produced, there will be less resources available to other members of the population. If there is an over production of offspring this will result in a struggle for survival within the species as the resources become scarce and individuals in the population will start to compete for these. This results in an increase in mortality rate as the weaker individuals in the population will lose out on these vital resources that are essential for their survival.

5.4.5 State that the members of a species show variation.

Members of a species show variation.

5.4.6 Explain how sexual reproduction promotes variation in a species.

Sexual reproduction is important for promoting variation as even though mutations form new genes or alleles, sexual reproduction forms a new combination of alleles. There are two stages in sexual reproduction that promote variation in a species. The first one is during meiosis during which a large variety of genetically different gametes are produced by each individual. The second stage is fertilisation. Here, alleles from two different individuals are brought together to form one new individual.

5.4.7 Explain how natural selection leads to evolution.

Individuals in a population differ from each other. Some individuals will have characteristics that make them well adapted to their environment whereas others will have characteristics that make them less adapted to their environment. The better adapted individuals are the ones that are more likely to survive and produce offspring while the less adapted ones are more likely to die. This is called natural selection. Natural selection results in the better adapted individuals to pass on their characteristics to more offspring as the lesser adapted ones are more likely to die before they reproduce. Over time, this result accumulates and a new generation is created with the favourable characteristics that makes this species better adapted to its environment. Natural selection has lead to the species evolving.

5.4.8 Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria.

Antibiotic resistance in bacteria is a common problem. It results from the transfer of a gene that gives resistance to a specific antibiotic usually by means of a plasmid to a bacterium. Some bacteria will then have this gene and become resistant to the specific antibiotic while others will lack the gene and so will die if exposed to the antibiotic. Over time, the non-resistant ones will all die off as doctors vaccinate patients, but the resistant ones will survive. Eventually, the resistant ones will be the only ones left as a result of natural selection and so a new antibiotic must be created. However, this has to be done on a regular basis as the bacteria keep evolving and become resistant to multiple antibiotics. 

The Peppered Moth is another example of evolution in response to environmental change. There are two types of these moths, one species has a light colour while the other one is darker. When Britain begun industrialising, the soot from the factories would land on trees and so the darker moths then had an advantage over the light ones as they could easily hide from predators. Before the soot, both types of moths were eaten by predators however now that the darker ones were able to hide the lighter ones got eaten more often.The population of the darker moths rapidly increased while that of the lighter ones rapidly decreased until only the dark moths were left. All the lighter moths were less adapted to the environmental change and so they could no longer survive in that new environment.