Theories of EvolutionStudents know the theory of evolutionThat there is evidence that evolution

has taken place.Some of the other theories of how life

began on EarthHSW – interpret evidence relating to

evolutionary theoryHSW – learn that the credibility of the

evidence may increase if it is consistent with existing ideas or

scientific consensus

Learning Outcomes

• All students know that the theory of evolution is the one accepted by most scientists

• Most students can state the theory of evolution and describe some of the evidence that evolution has taken place. They have some understanding of why Darwin’s theory of natural selection was only gradually accepted.

• Some students can identify the differences between evolution and other theories. They can suggest reasons for the different theories explaining life on Earth

Dates of theories: Lamarck (1809), Cuvier (1825) & Darwin (1844, but not published until 1859).

Theories for change

Cuvier

(1769-1832)

Darwin

(1809-1882)

Theories for change

Dates of theories: Lamarck (1809), Cuvier (1825) & Darwin (1844, but not published until 1859)

In the early 19th century:

1 The generally accepted date of the creation was 4004 BC.2 The Church taught that the Bible was the literal truth.3 More was known about variation and adaptation of animals

and plants than ever before.4 Many accepted that fossils were the remains of organisms

from the past.5 Scientists saw that different layers of rocks contained

different sets of fossils.6 Some taught that fossils showed that some living things

died out and were then replaced by others.7 The Earth’s crust is constantly changing . why not living

things?8 Small changes in living things had been observed.

The short-necked ancestors of modern giraffes needed to reach the leaves on tall trees when food was scarce.

Lamarck’s theory of evolution

How would this theory explain a giraffe’s long neck?

Over their lifetimes these giraffes stretched their necks; a trait which was then passed on to their offspring.

Jean-Baptiste Lamarck (1744-1829) was a French botanist who believed that species evolved because they inherited traits acquired through the over or under-use of body parts.

Lemarck’s theory of acquired characteristics

• Every type of animal evolved from primitive worms.

• He believed that the change from worms was causes by the inheritance of acquired characteristics.

• Useful changes in the parents are passed on to the offspring

( so body builders all have children with huge muscles?)

Who was Charles Darwin?

Darwin’s theory of evolutionThe British naturalist Charles Darwin (1809–1882) later suggested a more persuasive argument for evolution.

Darwin proposed that evolution took place through natural and sexual selection.

Darwin developed his theory of evolution after noticing close similarities between certain fossils and the adaptations of modern day animals he saw during his round-the-world voyage on the HMS Beagle.

Darwin’s theory of evolution

• That all living organisms have evolved from simpler life forms.

• This evolution comes about by a process of natural selection.

• Only those most suited to their environment survive – the survival of the fittest

Natural selection

Due to natural variation, the ancestors of modern giraffes would have had necks of different length.

How does Darwin’s theory explain a giraffe’s long neck?

How the giraffe got its neck

As a result, the long-necked giraffes were more likely to be healthy and live to produce more high-quality offspring.

This, in turn, would increase the chances of their long-necked characteristic (an adaptive trait) being passed on to future generations.

Giraffes with longer necks would have been able to reach more food than those with shorter necks.

Galápagos finches

Darwin thought all the finches could have evolved from one type of finch that came from the mainland.

Some finches had strong and claw-like beaks, suitable for crushing seeds.

Other finches had thin and delicate beaks, suitable for picking insects from holes in the ground.

In the Galápagos, Darwin noticed that different islands had different types of finches, with different types of beak.

Natural variation meant that some finches had slightly different beaks. These finches would have been able to eat different types of food and avoid competition. They wouldtherefore have survived and passed on their genes.

What happens when habitats change?

Adaptive evolution ensures that individuals within a species have traits allowing them to survive and reproduce in their habitat.

If the habitat changes, however, successful traits can become a disadvantage.

Individuals that fail to reproduce, compete effectively for food or survive against new predators will eventually die out. If the last individual of a species dies, the species is extinct.

For example, if global warming caused Arctic snow to melt, brown rabbits may be better camouflaged and so more likely to survive than white rabbits.

New theories are new, creative ideas

To get a theory accepted, you must explain how it

could happen (a mechanism)

A good theory may not always be accepted, even

when the evidence is.

Creationism• This is where people believe that God

made the world in seven days.

Intelligent design

• What is the theory of intelligent design?

• The theory of intelligent design holds that certain features of the universe and of living things are best explained by an intelligent cause, not an undirected process such as natural selection.

Is intelligent design incompatible with

evolution?• It depends on what one means by the word

"evolution." If one simply means "change over time," or even that living things are related by common ancestry, then there is no inherent conflict between evolutionary theory and intelligent design theory.

• However, the dominant theory of evolution today is neo-Darwinism, which contends that evolution is driven by natural selection acting on random mutations, an unpredictable and purposeless process that "has no discernable direction or goal, including survival of a species."

• It is this specific claim made by neo-Darwinism that intelligent design theory directly challenges.