10.4 evidence for evolution

developing the theory of evolution

• darwin carried out some of his most famous observations on finches in the Galapagos island

• he notices that different islands had finches with differently shaped claws and beaks

• through these observations, Darwin realised that the design of the finches’ beak was linked to the foods available on each island

• he concluded that a bird born with a beak more suited to the food available would survive longer than a bird whose beak was less suited

• therefore it would have more offspring, passing on its characteristics

• over time the finch population on that island would all share this characteristc

• Darwin published a book ‘on the origin of species’ which was his theory of natural selection

sources to study the process of evolution

palaeontology - the study of fossils and the fossil record

comparative anatomy - the study of similarities and differences between the chemical makeup of organisms

comparative biochemistry - similarities and differences between the chemical makeup of organisms

fossils

• formed when animal and plant remains are preserved in rocks

• over long periods of time, sediment is deposited on the earth to form layers of rock

• different layers correspond to different geological eras, the most recent layer being found on top

• within the different rock strata the fossils found are quite different, forming a sequence youngest to oldest which show that the organisms have changed over time

evidence provided by the fossil record

• fossils of the simplest organisms such as bacteria and simple algae are found in the oldest rocks, whilst fossils of more complex organisms such as vertebrates are found in some recent rocks. This supports the evolutionary theory that simple life forms gradually evolved over a long time period into more complex ones

• the sequence in which the organisms are found matches their ecological links to each other.

• by studying similarities in the anatomy of fossil organism, scientists can show how closely related organisms have evolved from the same ancestor

• fossils allow relationships between extinct and living organisms to be investigated

comparative anatomy

the study of the similarities and differences in the anatomy of different living species

homologous structure

• a structure that appears superficially different in different organisms but has the same underlying structure

• eg. the vertebrates limb are very similar between a walking vertebrates and a flying vertebrates therefore they have all evolved from the same common ancestor

• the presence of homologous structures provides evidence for divergent evolution - how from a common ancestor, different species have evolved with a different set of adaptive features

comparative biochemistry

• the study of similarities and differences in the proteins and other molecules that control life processes

• although these molecules can change over time, some molecules are highly conserved among species and can help to identify evolutionary links eg. ribosomal RNA

• to discover how closely 2 species are related, the molecular sequence of a particular molecule is compared. The number of different bases that exist are plotted against the rate at which the molecule undergoes neutral base substitutions. From this information, scientists can estimate the point as which two species shared a common ancestor