Chapter 7Sections 2 and 3

Chapter 7Sections 2 and 3

Section 2 How Does Evolution Occur?

• In the early 1800’s scientists figured out that the Earth is older than previously thought

• Bizarre fossils were found• Fossils were found in odd places • Seashell fossils found on

mountains

Charles Darwin

• Took the Beagle voyage in 1831

• Had a degree in theology

• Dad wanted him to be a doctor but he couldn’t watch surgery, it made him sick

Charles Darwin

• Darwin was really interested in studying plants and animals

• On his 5 year Beagle voyage, he served as a naturalist, a scientist that studies nature

• He took samples and notes about the plants and animals he saw on the trip

Natural Selection

• Darwin’s observations became the foundation for evolution by the mechanism of natural selection

• Natural selection is also known as survival of the fittest

• Individuals with favorable traits will survive and pass those traits into the next generation

Beagle Voyage

• Darwin’s trip traveled to the Galapagos Islands, formed by volcanoes, off the coast of Ecuador in South America

• Darwin noticed that finches on the islands were similar but different than the birds on the mainland and other islands

Beagle Voyage

Darwin’s Finches

• Darwin noticed the finches on the islands had different beak shapes and ate different foods

Finches

• Darwin thought the finches on the islands originated from finches on the mainland

• Darwin figured the wind from a storm helped the birds fly to the new islands

Return to England

• Darwin used three sources to develop his evolution theory– Farmers and breeders– Geologists like Charles Lyell– Thomas Malthus

Farmers and Breeders

• Selective breeding- traits are chosen that are favorable and only individuals with those traits are bred

• Example: Dogs – There are over 150 breeds selective

bred from the ancestral canine

In the wild

• For these types of changes to happen in the wild, it takes longer

• Variations in species is due to chance

Charles Lyell

• Darwin learned from Lyell that the earth was formed by natural processes over a long period of time

• Due to fossils and current species, Darwin had already thought changes in populations took a long time as well

– Charles Lyell

Thomas Malthus

• Darwin learned humans and other animals can produce more offspring than the food supply will support

• Starvation and disease will kill off the weak and the strong will survive to reproduce the next generation

• Thomas Malthus

Quanti

ty

Time

Increase versus Food Availability

Increase in human population

Increase infood supply

Natural Selction

• In 1858, Darwin started to collaborate with Alfred Russel Wallace

• In 1859, Darwin published his research, The Origin of Species by Means of Natural Selection

• Darwin believed natural selection is how evolution occurs

Alfred Russel Wallace

Natural Selection• Overproduction

– Species produce more offspring than will survive to maturity

• Genetic Variation– Individuals are different from each

other slightly– Some traits will increase chance of

survival and reproductive success while other traits will decrease chances

Natural Selection• Struggle to Survive

– Resources will vary in availability (food and water)

– Some will be killed while others survive

• Successful Reproduction– Well adapted individuals will

reproduce and produce offspring with similar “strong” traits while the weak will not live long enough to reproduce or only produce a few offspring

More Evidence

• 1930-40’s biologists combine genetic inheritance and Darwin’s theories to explain variance in population

• Variations are caused by mutations • Mutation- change in genes

Section 3

• Natural selection explains how a population changes over TIME.

• Generation time is the period between the birth of a generation and the birth of the next generation

Insect Resistance

• Some insects survive the farmer’s insecticides or poison and survive to produce offspring with the same genes until most of the population is adapted to resist the insecticide

Peppered Moths

• Peppered moths have 2 color variations, light and dark

• Before the industrial revolution the light moths blended into the trees better and were eaten less by birds and were more abundant in the population

• After the revolution, pollution made the trees darker and the darker moths were eaten less and more abundant

Peppered Moths

Formation of New Species• Separation

– Part of the population gets separated– Mountains, canyon, roads, river

• Adaptation– Environment changes in one area– Individuals adapt to that change

• Division– Populations become so different over

time they can no longer interbreed and become different species