Theory of Evolution

Learning Goals▪ Define "Evolution" & "Natural Selection".▪ Describe the 4 steps of Natural Selection,

giving an example of each. ▪ Explain the importance of "Variation".▪ Does Natural Selection act on an organism

phenotype or genotype? Explain!▪ List the 5 evidences that support the Theory

of Evolution.

Theory of Evolution

▪ EvolutionThe process of change over time.

• Specifically, a change in the frequency of a gene or allele in a population over time

Charles Darwin

▪ Father of Evolution▪ Proposed a mechanism for

evolution, natural selection▪ Darwin went on a 5-year trip

around the world on the ship, the HMS Beagle

• As the ship’s naturalist, he made observations of organisms in South America and the Galapagos Islands

•Wrote a book, “Origin of the Species”

Voyage of the Beagle

Voyage of Beagle

■ Dates: February 12th, 1831■ Captain: Charles Darwin■ Ship: H.M.S. Beagle■ Destination: Voyage around the world.■ Findings: evidence to propose a

revolutionary hypothesis about how life changes over time

Video on Darwin

https://youtu.be/6GNUlZhE_jE -Darwin

https://youtu.be/ZbITQ0dqxCQ Galapagos Island

https://youtu.be/XOiUZ3ycZwUTheory

Patterns of Diversity■ Darwin visited Argentina and Australia

which had similar grassland ecosystems.

◆ those grasslands were inhabited by very different animals.

◆ neither Argentina nor Australia was home to the sorts of animals that lived in European grasslands.

Patterns of Diversity

■ Darwin posed challenging questions.

◆ Why were there no rabbits in Australia, despite the presence of habitats that seemed perfect for them?

◆ Why were there no kangaroos in England?

Patterns of Diversity

■ Darwin collected the preserved remains of ancient organisms, called fossils.

■ Some of those fossils resembled organisms that were still alive today.

The Galapagos Island

The Galapagos Island

▪ Darwin was fascinated in particular by the land tortoises and marine iguanas in the Galápagos. ▪ Giant tortoises varied in predictable ways

from one island to another.▪ The shape of a tortoise's shell could be used

to identify which island a particular tortoise inhabited.

Animals found in the Galapagos

■ Land Tortoises

■ Darwin Finches

■ Marine Iguanas

Darwin’s Finches

The Journey Home

■ Darwin Observed that characteristics of many plants and animals vary greatly among the islands.

■ Hypothesis: Separate species may have arose from an original ancestor

Natural Selection

▪ Natural Selection: Organisms that are best adapted to an

environment survive and reproduce more than others

▪ Darwin’s Theory of Natural Selection occurs in four steps:

• Overproduction• Variation• Competition• Selection

1. Overproduction

▪ Each species produces more offspring that can survive

2. Variation

▪ Each individual has a unique combination of inherited traits.▪ Adaptation: an inherited

trait that increases an organism’s chances of survival

Why is Variation Important?

▪ Because the environment changes.▪ The more variation within a species, the

more likely it will survive• EX: If everyone is the same, they are all

vulnerable to the same environmental changes or diseases

▪ The more variation of types of species in an habitat, the more likely at least some will survive• EX: Dinosaurs replaced by mammals

Which community has a better chance of surviving a natural disaster?

Community A Community B

3. Competition

▪ Individuals COMPETE for limited resources:• Food, water, space, mates

▪ Natural selection occurs through “Survival of the fittest”▪ Fitness: the ability to survive and reproduce

▪ Not all individuals survive to adulthood

4. Selection▪ The individuals with the best traits /

adaptations will survive and have the opportunity to pass on it’s traits to offspring.• Natural selection acts on the phenotype

(physical appearance), not the genotype (genetic makeup)

• Ex: When a predator finds its prey, it is due to the prey’s physical characteristics, like color or slow speed, not the alleles (BB, Bb)

▪ Individuals with traits that are not well suited to their environment either die or leave few offspring.▪ Evolution occurs when good traits build

up in a population over many generations and bad traits are eliminated by the death of the individuals.

Peppered Moth

▪ Which moth will the bird catch?

A

B

Descent with Modification

▪ Descent with Modification – each living species has descended, with changes, from other species over time.

▪ Common Descent – all living organisms are related to one another

Evidence for Evolution:

▪ Fossil Record▪ Homologous Body Structures▪ Vestigial Organs▪ Embryology▪ Biochemical Evidence

The Fossil Record

▪ Fossils: a record of the history of life on Earth

Archaeopteryx

▪ Missing link between reptiles and birds

Homologous Body Structures▪ Homologous Body

Structures: similar anatomy in different types of animals because of common ancestor

Vestigial Organs

• Vestigial Organs: “leftover” traces of evolution that serve no purpose

Embryology

▪ Embryology: embryos of all vertebrates are very similar early on

Biochemical Evidence

▪ Biochemistry: DNA with more similar sequences suggest species are more closely related• EX: Humans and chimpanzees share

more than 98% of identical DNA sequences

Summary of Darwin’s Theory

■ Individuals in nature differ from one another■ Organisms in nature produce more offspring

than can survive, and many of those who do not survive do not reproduce.

■ Individuals best suited for the environment survive and reproduce most successful

■ Species change over time

Jean Baptist Lamarck 1800’s

Lamarck’s Theory of Evolution

▪ Tendency toward Perfection(Giraffe necks)

▪ Use and Disuse –▪ If a body part were used, it got stronger▪ If body part NOT used, it deteriorated

▪ Inheritance of Acquired Traits-▪ acquired changes were passed to offspring

▪ Lamarck’s Theory of Evolution:

● Giraffes all had SHORT necks originally

● Giraffe’s Necks got LONGER from stretching for food

● “Acquired” trait (long necks) then passed to offspring

● Giraffe population became long-necked

Lamarck’s Mistakes

▪ Was he correct??• NO!

▪ Traits are passed down from one generation to the next by GENES, not by an individual’s life experiences or activities

▪ Lamarck did NOT know how traits were inherited (Traits are passed through genes)

▪ Genes Are NOT Changed By Activities In Life▪ Change Through Mutation Occurs Before An Organism Is Born