SS3 First Term Biology Lesson Note – Evolution II

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WEEK  10

TOPIC: EVOLUTION

CONTENT:

1. Theories of Evolution.
2. The theories of evolution according to Charles Darwin, Jean Baptist de Lamark
3. Evidence of evolution.
4. Forces responsible for evolution: mutation, gene flow, genetic drift.

INTRODUCTIION

Adaptation is the process by which organisms change their structure, physiology and behaviour in order to survive. This has led to diversity in form, in structure and function among organisms.

The theory of evolution is an attempt to explain how this diversity has taken place. Many scholars made some discoveries on evolution, some of them are:

1. George Louis Buffon (1707-1777)
2. Carl Linnaeues (1707-1778)
3. Jean Lamarck (1744-1829)
4. Thomas Malthus (1766-1834)
5. Charles Darwin (1809-1882)
6. Alfred R. Wallace (19^th century)

SUB-TOPIC 1: THEORIES OF EVOLUTION

 LAMARCK’S THEORY (1744-1829)

In the early 19^th century, French biologist Jean Baptist Lamarck embraced the idea of progressive change in living world based in part on his study of marine invertebrate fossils.

He was the first biologist to suggest that organisms undergo evolution. He propounded his systematically organized theory of evolution in 1801. This theory is based on the following ideas.

1. The use and disuse of organs
2. The inheritance of acquired characteristics.

Lamarck believed that species do change over time (through use and disuse of the body parts) and that animals evolve because of unfavourable conditions that the animals try to adapt to.

In his explanation, Lamarck cited example of giraffe and said their ancestors had short neck but kept stretching their necks to reach leaves in high trees during the period of food scarcity. Lamarck posited that this voluntary, constant stretch of their neck slightly changed the hereditary characteristics controlling neck growth and that giraffe transmitted these acquired characteristics to its offspring.

Lamarck was right when he posited that we could acquire traits through voluntary use of body parts but was wrong when he concluded that these acquired characteristics are inheritable.

The following are the main points of the theory;

1. The environment forces an organism to have some needs.
2. To satisfy these needs, the organism may use an organ.
3. The organ that is frequently used develops.
4. Characteristics developed by an organism while satisfying the environmental needs are transferred to the offspring.
5. The organ that is not used degenerates.

Although the inheritance of acquired characteristics seems to be logical, no evidence has been found to support this view. Genetic materials are contained in the chromosomes. Except for rare mutations, genetical information is passed on unchanged from generation to generation. If acquired characteristics could be inherited, then children of a great sport person would be born with the knowledge of sports. Acquired skills are usually developed anew in each generation. They are certainly not inherited.

DAWIN’S THEORY OF NATURAL SELECTION

About 50 years after Lamarck proposed his theory of evolution, the British naturalist Charles Darwin, revolutionalized the thinking of most Biologists. In 1859, Darwin published a book called origin of species by means of natural selection. Like Lamarck, Darwin stated that living organisms gradually evolved adaptations to the environment. However, Darwin recognized the variations among members of a species. It is these variations rather than the acquired characteristics that aid natural selection.

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