Charles Darwin (1809-18= 82)

Born in western England
Had a consuming interest in nature as a = boy
Became a clergyman

-at that ti= me, most naturalists and scientists belonged to the clergy and viewed the world= in the context of natural theology

Field research helped D= arwin frame his view of life

The main mission of the five year v= oyage of the Beagle was to chart poorly known stretches of the South American coastline.

Darwin had the freedom to explore extens= ively on shore while the crew surveyed the coast.
He collected thousands of specimens of t= he exotic and diverse flora and fauna of South America.

Darwin noted that the plants and an= imals of South America were very distinct from those of Europe.

South American fossils more closely rese= mbled modern species from that continent than those from Europe.

The origin of the fauna of the Gala= pagos, 900 km west of the South American coast, especially puzzled Darwin.<= /p>

On further study after his voyage, = Darwin noted that while most of the animal species on the Galapagos lived nowhere else, they resembled species living on the South American mainland.<= /p>

It seemed that the islands had been colo= nized by plants and animals from the mainland that had then diversified on t= he different islands.

While on the Beagle, Da= rwin read Lyell's Principles of Geology

Lyell's ideas and his observations = on the voyage lead Darwin to doubt the church's position that the Earth was static= and only a few thousand years old.

-Instead, h= e was coming to the conclusion that the Earth was very old and constantly changin= g.

Darwin returned to Great Britain in= 1836

Darwin began to perceive that the o= rigin of new species and adaptation of species to the environment as closely rela= ted processes.

-For exampl= e, among the 13 types of finches that Darwin collected in the Galapagos, clear differences in the b= eak are adaptations to the foods available on their home islands.=

The Origin of Species

Two main points:

Evolution - the explanation for life's u= nity and diversity.
Natural seleection - the cause of adapti= ve evolution.

Central to Darwin's vie= w of the evolution of life is descent with modification

In descent with modification, all present day organisms = are related through descent from unknown ancestors in the past.

Descendents of these ancestors accumulated diverse modifications or adaptations that fit them to specific = ways of life and habitats.

Viewed from the perspective of desc= ent with modification, the history of life is like a tree with multiple branches from a common trunk.

-Closely re= lated species, the twigs of the tree, shared the same line of descent until their recent divergence from a common ancestor.

Theory of natural selec= tion

Natural selection is d= ifferential success in reproduction (un= equal ability of individuals to survive and reproduce).
Natural selection occurs through an interaction between the environment and the variability inherent among= the individual organisms making up a population.
The product of natural selection is the adaptation of populations of organisms to their environment.

Darwinian view of life<= /span>

Two main features:

The diverse forms of life have arisen by descent with modification from ancestral species.
The mechanism of modification has been n= atural selection working over enormous tracts of time.

If artificial selection can achieve such= major changes in a relatively short time, then natural selection should be capable of major modifications of species over hundreds or thousands of generations.
Evolution is measured as the change in relative proportions of heritable variation in a population over a succession of generations.

Darwin envisioned the diversity of = life as evolving by a gradual accumulation of minute changes through the actions= of natural selection operating over vast spans of time.

While natur= al selection involves interactions between individual organisms and their environment, it is not individuals, but populations that evolve.

(Populations are defined as a group of interbreeding individua= ls of a single species that share a common geographic area.)

Evolution is measured as the change= in relative proportions of heritable variation in a population over a successi= on of generations.