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Environmental Change & Evolution
Transcript of Environmental Change & Evolution
Charles Darwin (1809 - 1882)
Alfred Russel Wallace (1823 - 1913)
H.M.S. Beagle (1820 - 1870)
Organisms produce more offspring than are needed to replace the parents
"The elephant is reckoned the slowest breeder of all known animals, and I have taken some pains to estimate its probable minimum rate of natural increase; it will be safest to assume that it begins breeding when 30 years old and goes on breeding until 90 years old; if this be so, after a period from 740 to 750 years there would be nearly 19 million elephants descended from this first pair."
– Charles Darwin
Natural populations tend to remain stable in size over long periods
There is a competition for survival (a ‘struggle for existence’)
There is variation among the individuals of a given species
The best adapted variant have a selective advantage (survival of the fittest)
Changes within lines of descent over time.
Successive changes in allele frequencies in population as brought about by occurrences such as mutation, genetic drift, gene flow, and selection pressure.
Malaria and sickle cell anaemia
New species usually develop due to:
Geographical isolation (allopatric speciation)
Reproductive isolation (sympatric speciation)