Theory question 104
Evolution(a) Define the term "Organic Evolution"
(b) Outline the contributions of (i) Larmack; (ii) Darwin to organic evolution
(c) List three evidences of organic evolution
(d) Explain the role of (i) Mutation; (ii) Isolation in the formation of new species.
Show the model answer
(a) Organic evolution is the gradual change in living organisms over a very long time, by which complex forms developed from simpler ancestors.
(b)(i) Lamarck: use and disuse – organs that are used a lot develop, unused ones waste away; inheritance of acquired characters – such changes are passed to offspring (e.g. the long neck of the giraffe).
(ii) Darwin: theory of natural selection – organisms produce more young than can survive; there is a struggle for existence; offspring vary; those with useful variations survive (survival of the fittest) and pass them on; over many generations this produces new species.
(c) Any three: fossil records; comparative anatomy (homologous organs, e.g. pentadactyl limb); comparative embryology; vestigial organs; geographical distribution; molecular/biochemical similarities; observed changes such as industrial melanism.
(d)(i) Mutation: a sudden change in genes or chromosomes that produces new heritable variation, the raw material on which natural selection acts.
(ii) Isolation: when groups of a species are separated (geographically, by season or by behaviour), they cannot interbreed; each group changes in its own way until they can no longer interbreed and become separate species.
Lamarck = use and disuse; Darwin = natural selection.