EARLY THEORIES • Describe the two “laws” of Lamarck • History and observations of Darwin • theory • Application of the theories with • examples • Why Lamarck`s theory was rejected • Differences
Jean-Baptiste Lamarck • French Biologist (1744-1829) • Professor of “Worms and Insects” in Paris • The first scientific theory of evolution
Jean Baptiste de Lamarck • Two “Laws” • Law of use and disuse: Use or disuse causes structures to enlarge or shrink.
2. “Law” of inheritance of acquired traits • Acquired traits can be inherited • All such changes are heritable
Misuse • Legs of snake disappeared because it did not use them in its gliding movement; also their bodies became thin and long to allow them to crawl through narrow spaces
Lamarck`s “Law” rejected • His idea was that there is a ladder of life with superior forms (humans of course) near the top and lower forms on lower rungs (plants near the bottom). • Theory is deterministic. He imagined that all organisms had an internal drive to ascend the ladder during evolution. Those that started earlier (or had a stronger drive) would be higher than those that evolved later. He did not think of evolution in a tree-like form.
Lamarck`s “Law” rejected (Cont.) • He imagined that when an organism tries to use an organ for some purpose REPEATEDLY that organ will grow and, moreover, its offspring would start with an already enlarged organ. For example a giraffe would stretch for high leaves throughout its life and this would result in its offspring being borne with a longer neck and legs. • That there is no way that an event going on during an organisms life can causes directed changes in its HERITABLE MATERIAL.
Charles Darwin (1809 -1882) • English Naturalist • College dropout • Traveled around the world • Best known for On the Origin of Species (1859) • Abundant evidence for evolution • Proposed a mechanism: natural selection
Envisaged evolution as a tree A radical and novel view
Summary of Charles Darwin’s theory More individuals are born than survive to reproduce. 2. Variety exists among individuals of a species. 3. ‘Fitter’ individuals are more likely to reproduce = “Survival of the fittest”: Natural selection eliminates less well-adapted individuals. If characteristics are inherited, species slowly evolve. = adaptation, or ‘microevolution’ eventually giving rise to new species = speciation, or ‘macroevolution’.
Summary of Charles Darwin’s theory Evidence More individuals are born than survive to reproduce. Variety exists among individuals of a species. ‘Fitter’ individuals are more likely to reproduce = “Survival of the fittest”: Natural selection eliminates less well-adapted individuals. If characteristics are inherited, species slowly evolve = adaptation, or ‘microevolution’ eventually even giving rise to new species = speciation, or ‘macroevolution. Then Now
Summary of Darwin’s theory Based on Natural Selection observations: • Fraction of offspring survive to maturity • Natural resources are limited • Population size fluctuate around carrying capacity • A population has variations of similar traits • Traits best fitted to environment are passed on to next generation - unsuitable traits disappear
Differences: Theories of evolution Lamarck’s theory 1809 Darwin’s theory 1859
Tabulate differences Darwin • Offspring showed variation when produced • Change because of environmental factors • Natural selection – best suited • Best suited characteristics are passed inherited from parent to offspring Lamarck • Variation because individual change • Individuals in population change • Because they want to adapt to the environment • Change acquired inherited from parent to offspring