ON THE ORIGIN OF SPECIES

SBI3U

Created by Ms Mak

Darwin’s book ‘On the origin of species’ (1859) In 1844 Darwin wrote: “At last gleams of light

have come, and I am almost convinced that species are not immutable...”

In the same year he prepared a 231-page outline of his theory and gave it to his wife, with instruction that it be published should he die unexpectedly.

In June 1858, he received a letter from a young scientist, Alfred Russell Wallace. Wallace outlined his own theory of how species evolved.

Lyell and Hooker convinced Darwin to submit a paper along with Wallace’s at a meeting of the Linnean Society of London on July 1, 1858.

In November 1859 Darwin published a book ‘On the Origin of Species by Means of Natural Selection’.

SUMMARY OF DARWIN’S EVIDENCE

Plants and animals living in the Galapagos Islands closely resembled plants and animals living on the nearest continental coast (the west coast to south America).

Fossils of extinct animals (such as glyptodont) looked very similar to animals presently living in the same region (such as armadillo).

Species of animals (such as tortoises) that at first looked identical actually varied slightly from island to island in the Galapagos.

Finches collected in the Galapagos looked similar to the finches from South America but were, in fact, different species. Finch species also varied from island to island.

Evolution and natural selection

Darwin introduced the terms: Evolution: all the changes that have

transformed life on the Earth from its earliest beginnings to the diversity, which characterizes it today.

Natural Selection: the differential success in reproduction, in which its product is adaptation of organism to

their environment.

The theory of evolution by natural selection

Darwin described natural selection as the way in which the environment, or nature, favours the reproductive success of certain individuals over others.

Adaptation Herbert Spencer used the phrase

‘survival of the fittest’ to describe the process of natural selection.

Darwin understood that all species exhibit adaptations that make them well suited for survival or reproductive success in their environment.

DARWIN’S CONCLUSIONS

All species produce more offspring than can survive.

The offspring has to compete with one another for the limited resources available to them.

Individuals in every population vary.

The offspring with the most favorable traits or variations are the most likely to survive and produce more offspring.

All the processes for change are slow and gradual.

PREDICTION

The theory of evolution predicts: that species will evolve in response to climate

change bird species may change the timing of migration

proved plants may adapt to warmer or drier conditions:

proved the evolution of antibiotic resistance in bacteria:

proved the evolution of pesticide resistance in insects:

proved Darwin predicted that fossils of the most primitive

human ancestors would be found on African continent:

proved

SUMMARY

Darwin theory of evolution by means of natural selection:

explains how the environment acts to favour the reproductive success of individuals with certain heritable traits.

is able to explain how an adaptation can arise.

can be used to make predictions about the future evolution of species.

is a testable scientific theory.