Darwin’s Theory of Evolution

Ch. 15 - 16

Evolutionary Theory

• Collection of scientific facts, observations, and hypotheses

• Evolution – change over time• Theory – well-supported testable explanation of

phenomena that have occurred

• I AM TEACHING YOU ABOUT A THEORY, JUST LIKE THE BIG BANG THEORY, OR HAVING A THEORY AS TO WHY SOME OF YOU LIKE PIZZA.

Darwin

• 1831 – Darwin joined the Beagle and set sail around the world

• He was interested in nature and organisms• He collected evidence, samples, notes,

observations, etc.• He put this evidence together to come up with

his theory of evolution.

Darwin and the Galapagos Islands

• Darwin traveled to the islands• He noticed that each island had its own

climate – some dry, some rainy, some humid, etc.

• The plants and animals on each island were different

• Each island had its own “version” of a tortoise, but they were different on each island… why?

Darwin’s Observations

• Variation – he noticed that all species had variations of them– Tortoises – different shells– Finches – different beaks

Darwin’s Conclusion

• Natural selection – “survival of the fittest”• All organisms struggle to survive – compete

for food, mates,, space, etc.• Any adaptation that increases the chance of

survival will stick around– Speed, camouflage, protection, etc.

Natural Selection

• Example – mole rats• Some have big claws for digging, some have

sharp claws for climbing, and some have no claws

• All the mole rats live together with a predator• The predator has good sight and smell, can

climb, but can’t dig• Which mole rats are more likely to survive?

Darwin’s Finches

• The Galapagos islands also have varieties of finches

• Each subspecies of finch has a different beak

• Each subspecies of finch has a different diet

Natural Selection

• Those organisms with favorable traits will survive and pass on their characteristics to their offspring

• Another example:– 3 types of spiders

• Big – easily seen by predators• Small – can’t find food• Medium - survive

– after many generations which size spider is likely to be around?

Natural Selection• Survival of the biggest?

– NO!• Survival of the fastest?

– NO!• Survival of the lightest?

– NO!• Survival of the fittest?

– YES!

• What does that mean?– Best adapted for their situation

Current Evidence for Evolution

• 4 pieces of evidence currently support evolution– Fossils– Geographic distribution– Homologous body structures– Similarities in embryology

Fossil Evidence

• Fossil – remains of ancient life• Fossils are found in layers• Older layers contain organisms that are not

found in younger layers• This indicates they were present but did not

survive

Geographic Distribution Evidence

• There are organisms living on different continents with similar traits

• Example – p. 383– Each organism has very similar characteristics that

helps it adapt to its environment, which are also similar

Homologous Body Structure Evidence

• Structures that have different mature forms, but the same embryonic tissues

• This supports that all 4-limbed organisms evolved from a common ancestor

Embryology Evidence

• Supports homologous structures

• Many organisms with backbones look very similar during early embryonic development

Summary of Darwin’s Theory

• All species have variation• These variations are either favorable or not• The favorable variations help organisms

survive – those traits will stick around• Unfavorable variations do not help organisms

survive – those traits will eventually disappear• Organisms with similar traits evolved from a

common ancestor