DARWIN’S THEORY OF EVOLUTIONSearcy Ninth Grade Center 2014

Darwin Presents His Case

15.3

Darwin’s Findings

After Darwin returned to England in 1836 he filled notebooks with his ideas about species diversity and the process that he would later call evolution.

He did not rush to publish his ideas because they disagreed with the fundamental scientific beliefs of his day.

He asked his wife to publish his ideas when he died.

Play video

Wallace’s Essay

In 1858, another naturalist, Alfred Russell Wallace wrote an essay describing his work in Malaysia that summarized the same ideas Darwin had been thinking about for 25 years.

Origin of Species

Suddenly Darwin had incentive to publish the results of his work.

In 1859 On the Origin of Species presented evidence and proposed a mechanism for evolution that he called natural selection.

Evolution is a THEORY

A theory is a well-supported, testable explanation of phenomena that have occurred in the natural world, like the theory of gravitational attraction, cell theory, or atomic theory.

Keys to Darwin’s Theory

Genetic variation is found naturally in all populations.

Keys to Darwin’s Theory

Struggle for existence means that members of each species must compete for food, space, and other resources.

Keys to Darwin’s Theory

Some organisms in a population are less likely to survive.

Keys to Darwin’s Theory

Survival of the fittest organisms which are better adapted to the environment will survive andreproduce, passing on their genes.

Vocabulary

Ability of an individual to survive and reproduce in its specific environment = fitness.

Hmmm…

Vocabulary

Any inherited characteristic that increases an organism’s chance of survival = adaptation.

What is Darwin’s Theory? Over time, natural selection results in changes

in the inherited characteristics of a population. These changes increase a species’ fitness in

their environment. How does it work?

Descent with modification suggests that each species has descended with changes, from other species over time.

This idea suggests that all living species are related to each other; and that all species, living and extinct, share a common ancestor.

Evidence of Evolution

Artificial selection Fossil record Geographic distribution Homologous structures Embryology DNA Visual record natural selection

happening

Artificial Selection

In artificial selection, nature provides the variation through mutation and sexual reproduction; and humans select those traits that they find important.

Examples: cows bred to produce more milk; turkeys with more breast meat, etc.

Dogs: Artificial Selection

Chihuahua – bred from Techichi of Mexico by Mayans, had religious

significance.

Dachshund – bred in Germany as earlyas the 15th century to hunt badgers.

Saint Bernard – bred by monks around 1050 A.D. to

rescue travelers of mountain passes in the Swiss Alps

between Italy and Switzerland

Artificial Selection

Proof of Evolution

Fossil Record – Fossils are the remains of ancient organisms found in layers of rock in the Earth.

Proof of Evolution

The layers of rock tell the history of the Earth, while the fossils found within the rock tell a history of life.

The fossils are thought to be the same age as the rock they are found in.

Movement of Earth’s Crust

Sea Level

Sedimentary rocks form in

horizontal layers.

When part of Earth’s crust is compressed, a bend in a rock forms, tilting

the rock layers.

As the surface erodes due to water, wind,

waves, or glaciers, the older rock surface is exposed.

Fish die inthe oceanand arecovered insediment.Over timeand underincreasingpressure,the remainsbecomesfossilized

Earthquakes and volcanoes cause uplifting of the layers of the Earth,

taking the fossils along.Fossils ofmarinefish foundon the mountain sides ofsouthwestWyoming,which atone timewas covered by aninland sea

Transitional Fossils

Verifying Darwin’s Findings If Darwin’s theory is correct, one would

expect to find closely related yet different species living in a geographic region as they spread into nearby habitats and evolve…

Tortoises adapted to different habitats as they spread from the mainland to the different islands. = Divergent Evolution = Adaptive Radiation.

Adaptive Radiation

Little vegetationLong necks

Lots of vegetationShort necks

Intermediate vegetation

Intermediate necks

Adaptive Radiation

The beaks of Galapagos finches have adapted to eating a variety of foods.

Verifying Darwin’s Findings If Darwin’s theory is correct you would also

expect to find different species living far apart in geographic regions with similar habitats becoming more alike as they adapt to similar ecosystems.

Whales and sharks have a similar body design even though they are very different organisms (one is a fish; the other, a mammal) because they have independently adapted to living in a similar environment = Convergent Evolution.

Geographic Distribution

Beaver

NORTH AMERICA

Muskrat

CapybaraSOUTH

AMERICA

Coypu

Beaver

Muskrat

Beaver andMuskrat

Coypu

Capybara

Coypu andCapybara

Beaver and capybaraare closely-related species living in very different environments,while beaver and musk-rat are distantly-related species living in a similar environment.Differences betweenbeaver and capybarashow divergent evolution, while similaritiesbetween beaver andmuskrat show convergent evolution.

Differences between closely-related muskratand coypu show divergent evolution, while similarities between distantly-related capybaraand coypu show convergent evolution.

Homologous Structures

Structures, like the limbs of vertebrates, look very different, but are made from the same bones, because they are made from the same clump of undifferentiated cells in the embryo.

Homologous Structures

Turtle Alligator

Bird Mammal

Ancient lobe-finned fish

Homologous Body Structures Some homologous body structures are

vestigial and have no useful function even though they are still present, like hipbones in

whales and boa constrictors, or a tail and cecum (appendix) in humans.

Vestigial structures such as pelvic bones in the baleen whale are evidence of evolution.

Why Grow a Tail; or Legs… The human embryo has a

tail at 4 weeks; which disappears at about 8 weeks.

Skinks are a type of lizard. In some species, legs have become so small they no longer function in walking.

One explanation: The gene code is present to make the organ,

but the function has been lost through change over time. If the organ is not vital to survival, then natural selection would not cause its elimination.

Similarities in Embryology Embryos of

many animals with back-bones are very similar.

It is clear that the same groups of undifferentiated cells develop in the same order to produce the same tissues and organs of all vertebrates, suggesting that they all evolved from a common ancestor.

Similarities in DNA

Similarities in DNA and protein sequences suggest relatedness.

Similarities in Karyotypes Similar karyotypes suggest an

evolutionary relationship.

Human- 46 chromosomes Chimpanzee- 48 chromosomes

Visual Evolution

Peppered Moth There is a natural variation in populations

of peppered moths. Typica form – lighter Carbonaria form - darker

Peppered Moth

The light colored form was the predominant form in England prior to the Industrial Revolution.

Around the middle of the 19th century the darker form began to appear. It was first reported in 1848. By 1895 98% of the moths in Manchester were the dark variety.

In recent years, the burning of cleaner fuels and Clean Air regulations has reduced

the pollution there and the lighter colored moths have

increased in numbers. https://www.youtube.com/watch?v=aTftyFboC_M