Evidence for evolution

Palaeontology This involves the collection of evidence of past life or f The fossil record shows: changes in some species such as similarities between prehistoric organisms and organisms living today eg mammoths & elephants some organisms have changed little throughout their history. This may be due to little change in the selection pressures they face These organisms are called living fossils eg coelacanth, crocodile, cockroach Some problems with using fossils include incomplete records eg human records problems with dating eg changing CO2 levels affect carbon dating

Comparative Embryology Similar organisms pass through similar stages of development. The closer the similarities in the appearance of the embryo/foetus at each stage, the greater the degree of relationship inferred. Some scientists believe the development from egg to complete organism may reflect the evolutionary history of that organism, as many embryos possess structures which are not found in the adult, but appear in organisms in the ancestral tree eg gill slits and tails in all mammals (including humans)

Comparative anatomy This refers to Homologous structures are structures that are similar due to common ancestors on the evolutionary tree Examples include forelimbs of vertebrates Vestigial structures are reduced structures or remnants of structures once possessed Examples include pelvis of whales, human canine & appendix These structures indicate changes in structure & ancestral link to those possessing full structures One problem with comparative anatomy is the presence of analogous structures, which are structures that are similar to similar selection pressures, not common ancestry Examples include wings of birds and beetles, body shape of dolphins and sharks Phylogenetic trees are diagrams showing evolutionary relationships

Biogeography This refers to studies of the distribution of species, which suggest dispersal patterns and evolutionary history Examples include finches and other animals of Galopagos and other isolated islands, differences between species either side of the Wallace line (Australasia and Asia)

Biochemistry and Molecular Biology This involves the study of proteins and DNA in closely related organisms. The fact that closely related species have similar chemistry is seen as further evidence for evolution. Studies of proteins involve looking at amino acid sequences in common proteins shared by different species As amino acids are linked in sequences determined by the DNA, differences in amino acid sequences indicate the genetic composition of the organisms. The greater the similarities, the greater the degree of relationship presumed

DNA DNA studies involve the analysis of the nucleotide sequences (gene sequences) Genetic linkage groups involves looking at groups of genes close together on the same chromosomes DNA sequencing involves breaking up DNA into chunks to identify the actual sequence of bases in the DNA DNA hybridisation involves splitting DNA and merging strands from different species to look for differences in the chains Sources of DNA include nuclear DNA, mitochondrial DNA & chloroplast DNA (plants)

Immunology A new technique that has immerged uses immunology to research the degree of relationship between species. This technique involves looking at antigens in different species. The closer the relationship, the more antigens will be had in common

Artificial breeding This refers to human selection by breeding for particular characteristics (artificial selection) Examples include domestic animals (eg dogs, cats, cows, sheep, pigs, pigeons, etc) and plants (eg wheat, rice, fruit & vegetables) - Brussel sprouts, cauliflower, broccoli and cabbage have all been developed from the Kale plant.

Lamarck v Darwin

Evolutionary theory What contributions have the following played? Mendel: provided the concept of the gene (package for inheritance) and the rules of genetics (how things are inherited) Lyell: provided the idea of constant geological change and the extremely long time span available in the life of the planet Malthus: provided the idea that populations increase faster than the food supply Wallace: discovered the Wallace line – differences between species in Australasia and Asia & came up with the same ideas of natural selection as Darwin Cricks, Watson and Wilson: discovered the molecular structure of DNA