1. NIS - BIOLOGY
Lecture 63 – Lecture 64
Darwin’s Theory of Evolution by Natural Selection
Ozgur Unal

2. Developing the Theory of Evolution
About 200 years ago, the average person believed that the world was about 6000 years old.
Almost everyone thought that animals and plants were unchanging.
In 1831, young Charles Darwin boarded the HMS Beagle, which set sail from England.
The primary mission of Beagle was to survey the
coast of South America.
Darwin’s role on the ship was as naturalist and
companion to the captain.

3. Developing the Theory of Evolution
Over the course of the ship’s 5-year voyage, Darwin made extensive collections of rocks, fossils, plants and animals.
He also read a copy of Charles Lyell’s Principles of Geology – a book proposing that Earth was millions of years old.

4. Developing the Theory of Evolution
In 1835, the Beagle arrived in the Galapagos Islands off the coast of South America.
These volcanic islands contain their own, slightly different varieties of animals.
After he returned to England, he found
out that almost every specimen he
collected on the islands was new to
European scientists.
Darwin began to suspect that the
populations from the mainland (South
America) changed after reaching the
Galapagos.

5. Artificial Selection
Darwin hypothesized that new species could appear gradually through small changes in ancestral species. How?
The process of directed breeding to produce offspring with desired traits, referred to as selective breeding in Chapter 13 was called artificial breeding by Darwin.
Artificial breeding also occurs when developing new breeds of dogs or new strains of crop plants.
Darwin inferred that if humans could change species by artificial selection, then perhaps the same process could work in nature.
Darwin thought that given enough time, perhaps this process could produce new species.

6. Natural Selection
After reading Thomas Malthus’ ideas on the effects of increasing human population, Darwin thought that these ideas could be applied to the natural world.
Darwin reasoned that some competitors in the struggle for existence would be better equipped for survival than others.
Those less equipped would die  process of natural selection

7. Natural Selection
Darwin’s theory of evolution by natural selection has 4 basic principles:
1- Individuals in a population show differences or variations.
2- Variations can be inherited, meaning that they are passed down from parent to offspring.
3- Organisms have more offspring than can survive on available resources.
4- Variations that increase reproductive success will have a greater chance of being passed on than those that do not increase reproductive success.

8. Natural Selection
Darwin’s finches:

9. Natural Selection
Today, biologists use the term evolution to define cumulative changes in groups of organisms through time.
Natural selection is not synonymous with evolution; it is a mechanism by which evolution occurs.
Is an individual organism able to evolve over the course of its life?