Evolution

Starter What do you remember about evolution from GCSE?

Learning Objectives Success criteria Understanding the mechanisms evolution and examining the evidence Success criteria Learners should be able to demonstrate and apply their knowledge and understanding of: the evidence for the theory of evolution by natural selection To include the contribution of Darwin and Wallace in formulating the theory of evolution by natural selection AND fossil, DNA (only genomic DNA at AS level) and molecular evidence.

What is evolution? Evolution is the cumulative change in the heritable characteristics of a population. Cumulative change – small changes upon small changes over many generations Heritable characteristics – gene-controlled factors Population – not an individual

Developing the theory of evolution Using p286 write a brief summary of the history of the development of the theory of evolution. Include : Contributions from Darwin and Wallace Observations and conclusions 10 mins

Evidence for evolution Palaeontology Comparative anatomy Comparative biochemistry

Palaeontology Fossil record: A fossil is the ancient preserved remains of an organism. The fossil can be dated from the age of the rock formation. Sequences of fossil can show the gradual change of an organism over geological time. Continuous fossil records are rare as: many organisms are soft-bodied and decompose quickly Conditions for fossilisation are not always present Many fossils have been destroyed or remain undiscovered

Palaeontology Evidence provided by the fossil record: Gradual change - Simplest organisms are found in older rocks Sequence matches ecological links - Plants fossils appear before animal fossils Closely related organisms have a common ancestor -studying similar anatomy of fossils Fossils allow relationships between living and extinct organisms to be investigated

Comparative anatomy Homologous structures: All of life is connected through evolutionary history and consequently those organisms more closely connected might reasonably be expected to share common structures or homologous. Group of organisms closely related share a common form or derived trait which has been inherited from the common ancestor. Homologous structures provide evidence for divergent evolution

Homologous structures A classic example of homologous structures is the pentadactyl limb of the vertebrate. a) Humerus b) Radius c) Ulna In each example the bones are modified and adapted to the locomotion of the animal. In homologous structures it is normal to find that parts of the structure will be modified, enlarged or reduced (vestigial).

Comparative biochemistry Certain molecules are found throughout the living world Two closely related species will have separated only relatively recently will have very similar biological molecules Similarity in biological molecules Cytochrome c – a protein used in respiration Ribosomal RNA

Comparative biochemistry Neutral variations in the molecular structure of a molecule do not affect its function and therefore are not affected by natural selection. They occur at a fairly regular rate (different for different molecules). By comparing the molecular sequence scientists can estimate the point at which 2 species separated. Species that are closely related have more similar DNA and proteins

Plenary - exam question June 2011 q.3