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Evolution is a process that results in heritable changes in a population spread over many generations • Variation • Natural Selection • Evolution
Aristotle • 384-322 BC- believed living things could be arranged in a hierarchy- Scala Naturae- a ‘ladder of nature’ • Simplest creatures on the bottom rung, man on the top rung, other arranged in between • Scientists supported this until late 19th century- it explained why organisms seemed perfectly adapted to their environment, role in nature
The idea of evolution isn’t new- • School of Greek Philosophy, founded by Anaximander (611-547 BC) proposed an atomic theory and an evolutionary theory similar to modern views • However, this work was unknown in Europe during formation of the science of Biology
Georges de Buffon • 1707-1788- proposed species might undergo change in the course of time • Suggested that in addition to the creatures of the world, there might be “lesser families conceived by nature and produced by time” • These changes occur through a process of improvement/degeneration
Erasmus Darwin • 1731-1802- grandfather of Darwin • Suggested species have historical connections with one another • Animals may change in response to their environment • Polar bear- ordinary bear, but living in the Arctic ‘modified’ it- those traits were passed on
James Hutton • 1726-1797- geologist- proposed that earth’s features were created by slow, gradual processes, not sudden violent events • Important for 2 reasons • Earth had a long history- long enough for evolutionary changes • Stated that change itself is the normal course of events
William Smith • 1769-1839- studied fossil distribution scientifically- • Noticed the order of geologic strata, collected fossils from each layer • Each stratum, regardless of location, contained characteristic fossils- used to identify layers • Implies present surface had been formed layer by layer
Georges Cuvier • 1769-1832 – Recognized that fossils showed many species had existed (but no longer exist) • Proposed extinction of species due to catastrophes. • Couldn’t explain where new species came from • Vocal opponent of evolutionary theory.
Jean Baptiste Lamarck • 1744-1832 – Worked out a systematic concept of evolution. • 1801 he proposed that all species, including Homo sapiens, are descended from other species. • Everything derived from an earlier, less complex species.
Inheritance of acquired characteristics- characteristics of organisms become stronger/weaker, larger/smaller, more/less through use or disuse. These changes are transmitted from parent to their progeny – ex. Giraffes neck!
Evolution was a universal principle – unconscious striving upward on the Scala Naturae that moved all organisms to more complexity.
Charles Lyell • 1797-1875 – Geologist provided new evidence to support Uniformitarianism. • Uniformitarianism – Slow, steady, cumulative effect of natural forces produced continuous change in the course of Earth’s history. • Since process was slow, results being barely visible in a lifetime, must have been going on for a very long time.
Thomas Malthus • Influenced both Darwin and Wallace with his work on populations • Warned that human population was increasing so rapidly that food supplies would run out • Food supplies and other factors keep populations in check
Alfred Russel Wallace • Biologist, naturalist, explorer • Studied geographical distribution of animal species- biogeography • Influenced by Malthus, realized that species diverge from similar ones due to environmental pressures • Developed his own theory of evolution, very similar to Darwin’s
Charles Darwin • 1809-1882 – The father of evolution. • Naturalist – accompanied HMS Beagle as ship’s naturalist. • Explored fossil beds in S. America. • Collected specimens of plant, animal life he encountered. • Observed that varieties of animals differed on east and west coast.
Galapagos Islands –sailors could tell island origins of tortoises based on appearance. • Also noted that island finches varied in size, shape of bodies, beak, type of food eaten. • Observed that islands were young, plants, animals on islands differed from those on mainland, and from each other.
Influenced by Malthus, realized that populations could easily reach limits of resources • Something had to keep populations in check- 1 pair of elephants => 19 million elephants in 750 years, but average number of elephants remains constant • Natural selection- environment ‘determines’ which individuals survive and reproduce
Natural selection is analogous to artificial selection used by breeders of cattle, dogs, crops, etc. Humans choose individual specimens for breeding based on desirable characteristics • Natural selection- environment ‘decides’ • Individuals with certain hereditary characteristics survive and reproduce, other individuals with other traits are eliminated, population slowly changes. • EX- horses that can run faster, escape predators survive, reproduce, offspring, in turn, might be faster
Inherited variations are a matter of chance- not produced by environment or ‘creative force’ or unconscious striving of the organism. • Variations, in themselves, have no goal or direction- often have positive or negative adaptive value- more or less useful to an organisms survival and reproduction.
It is the operation of natural selection – interaction of individual organisms with their environment- over a series of generations that gives direction to evolution. A variation that gives even a slight advantage makes that organism more likely to leave surviving offspring.
Essential difference between Darwin, predecessors is variation- Darwin found variation to be part of the fabric of evolutionary process. Species arise when differences among individuals within a group are gradually converted in to differences between groups as the groups become separated in space and time.