Theory of Evolution
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