Darwin’s Theory of Evolution

Science’s Answer to the Question:

“Where Did Life on Earth Come From?”

Charles Darwin (Feb. 12, 1809 - April 14,

1882)• Robert Darwin, father, and Erasmus Darwin, grandfather - both physicians and Unitarian free thinkers.

• Quit physician training to become a minister. Most naturalists in 1800’s were ministers who studied “natural theology,” which sought to discover the Creator’s plan and purpose for all creatures.

• Voyage of the HSM Beagle (1831-1836). • Married first cousin Emma Wedgwood, 1838• Devoted father to his 10 children – involved his children in his experiments. Despite their shallow gene pool, his children were quite successful

• On the Origin of Species (1859)

Figure 22.5

EnglandEUROPE

NORTHAMERICA

GalápagosIslands

Darwin in 1840,after his return

SOUTHAMERICA

Cape ofGood Hope

Cape Horn

Tierra del Fuego

AFRICA HMS Beagle in port

AUSTRALIA

Tasmania

NewZealand

PACIFICOCEAN

An

des

ATLANTICOCEAN

Voyage of the HMS Beagle 1831

- - He collected many plant and animal specimens from the Galapagos Islands off South America . - He studied his finch collections, especially the differences in their beaks, when he got home and began to make connections between adaptations and how new species originated (speciation). (which is why The Origin of Species became his book title…)

•The historical

context of

Darwin’s life

and ideas

Figure 22.2

Linnaeus (classification)

Hutton (gradual geologic change)

Lamarck (species can change)

Malthus (population limits)

Cuvier (fossils, extinction)

Lyell (modern geology – Earth is old

Darwin (evolution, nutural selection)

Mendel (inheritance)

Wallace (evolution, natural selection)

1750

American Revolution French Revolution U.S. Civil War

1800 1850 1900

1795 Hutton proposes his theory of gradualism.

1798 Malthus publishes “Essay on the Principle of Population.”

1809 Lamarck publishes his theory of evolution.

1830 Lyell publishes Principles of Geology.

1831–1836 Darwin travels around the world on HMS Beagle.

Darwin begins his notebooks on the origin of species.1837

Darwin writes his essay on the origin of species.1844

Wallace sends his theory to Darwin.1858

The Origin of Species is published.1859

Mendel publishes inheritance papers.1865

Artificial Selection – selective breeding by farmers changes species over time

Darwin connected and built on others’ ideas

• If the Earth is very old and has gradually changed over time…and if plants and animals have also changed over great periods of time… and if animals can be artificially bred to change…and if there is competition for survival…

• He connected the dots between Cuvier, Lamarck, Hutton, Lyell, Malthus, and what he saw with selective breeding of plants and animals (artificial selection) ….

NATURAL SELECTION• Darwin made the connection that individuals in all species compete for survival, that successful individuals survive and pass on their genes, and in this way the entire species adapts to its environment.

• Over time, these adaptations can accumulate to create new species.

• He called this process natural selection. He also called it “survival of the fittest.”

• How do “successful” individuals get their “good” genes? ……..

•Darwin developed two main ideas

-Natural selection – mechanism by which fit individuals survive and pass on their genes. Unfit individuals do not.

-Evolution -natural selection causes change over time, or evolution. This explains life’s unity and diversity – all life on earth descended from a common ancestor (life’s unity) and then evolved into all the diversity that has ever existed on Earth (99% of which is already extinct!)

**Natural selection is the mechanism; evolution is the result*

-

•He used the phrase descent with modification to capture both ideas.

– Descent captured his idea of a common ancestor from which all life descended

–Modification captured his idea of adaptations leading to diversity.

“Fitness”Darwin called the ability of an organism to survive and reproduce in its specific environment “fitness.”

Fitness is NOT just the strongest or the

fastest! • Can be the sneakiest! Or best camouflaged….

• And you have to reproduce or its all for nothing evolutionarily speaking….

Descent with Modification =

Theory of Evolution The characteristics of new species are not entirely new, but rather modified

versions of ancestor characteristics.

…..Evolution is a process of

remodeling, not inventing. Mother Nature can only work with the material she has.

…..

In 1844, Darwin wrote a long essay on the origin of species and natural selection…- But he was reluctant to introduce his theory publicly, anticipating the uproar it would cause. -At the time, most people believed that the Earth was 6,000 years old and that all species had been created by the Creator all at once. His theory of evolution is incompatible with this view. - In June 1858 Darwin received a manuscript from Alfred Russell Wallace (in Indonesia) who had developed the theory of natural selection independently of Darwin.Darwin quickly finished The Origin of Species and published it the next year, 16 years after he had written it. -

What is the Proof of Evolution?

Evidence for Evolution: Outline

• Research Interventions…human made evolution

• Homology – Evidence of Remodeling– Anatomical Homology– Vestigial Structures (snake pelvis, appendix)

– Embryological Homologies– Molecular Homologies

• The Fossil Record Corroborates Evolution

• Transitional Fossils – • Biogeography - bears, marsupials and placentals

Evolution Research Example:

Reznick and Endler, 1982 Paper Reznick and Endler transplanted guppies from pike-cichlid pools to killifish pools

and measured the average age and size of guppies at maturity over an 11-year period (30 to 60 generations).

EXPERIMENT

Pools with killifish,but not guppies priorto transplant

Experimentaltransplant ofguppiesPredator: Killifish; preys

mainly on small guppies

Guppies:Larger atsexual maturitythan those in“pike-cichlid pools”

Predator: Pike-cichlid; preys mainly on large guppies

Guppies: Smaller at sexual maturity thanthose in “killifish pools”

Figure 22.12

They watched evolution happen….

RESULTS After 11 years, the average size and age at maturity of guppies in the transplanted populations increased compared to those of guppies in control populations.

161.5185.6

67.5

Wei

ght

of g

upp

ies

at m

atur

ity (

mg)

Age

of

gupp

ies

at m

atur

ity (

days

)

92.3

48.5

Control Population: Guppiesfrom pools with pike-cichlids as predators

Experimental Population:Guppies transplanted topools with killifish aspredators

76.1

Males Females

85.7

58.2

Males Females

CONCLUSION Reznick and Endler concluded that the change in predator resulted in different variations in the population (larger size and faster maturation) being favored. Over a relatively short time, this altered selection pressure resulted in an observable evolutionary change in the experimental population.

Homologous Structures - structures that have the same ancestral origin and develop from same embryonic tissue, but have evolved to fit their environment and have different mature forms in different species. - Not separately engineered – remodeled by natural selection…Mother Nature can only work with the material she has!

Forelimbs Up Close

Can you think of other homologous structures?

Evolution.berkeley.edu

Vestigial Structures

•Structures that no longer have a use •Remnants of structures that were once useful….•Examples in humans: wisdom teeth, coccyx, appendix, Darwin’s Tubercle•What was the ancestral purpose of these structures?•Why do we still have them?

Embryology

• Embryonic stages reveal anatomical homologies that disappear in adult organisms

• In vertebrates, the same groups of embryonic cells develop in the same order and in similar patterns

• The embryo “is the animal in its less modified state,” which “reveals the structure of its progenitor”

Embryology

Figure 22.18

Transitional Fossils: Evolutionary transitions have left signs in the

fossil record

• Fossilized whales have traits that link today’s whales to their terrestrial ancestors. Fossilized leg bones of Basilosaurus and Ambulocetus show the hind limbs of whale ancestors

Human Transitional Fossil:

Australopithecus Afarensis

Molecular Homologies

•Because the genetic code is universal in all living things, molecular biology can now explore evolutionary relationships between very different species (plants, animals, fungus, bacteria…) •If two species have some gene and protein sequences that match closely, the sequences have probably come from a common ancestor•More on this when we discuss classification systems…

Biogeography

• The distribution of species• Gave Darwin his first clue about evolution: Similar species live near each other because they have descended from a common ancestor.

• Islands are showcases for biogeopraphic evidence because they are isolated

Australian Marsupials are closely related – all evolved from a common

ancestor + therefore have common characteristics

Convergence: Evolution’s Wild CardNot all similarity represents

common ancestry! •Species from different evolutionary branches may resemble each other because they evolved similar adaptations in similar environments….in other words, by coincidence•This is called convergent evolution and the similar traits are called analogies (not homologies!)

Sugar Gliders and Flying Squirrels

Convergence: • Dolphins and Sharks

Sharks and Dolphins

•Dolphins are aquatic mammals•Sharks are cartilaginous fish (along with rays and skates) • They separately evolved similar traits as aquatic predators: Dorsal fins, fusiform body shape, coloration•These are analogous traits

Sea Lions and Seals

Convergence

• Sealions and seals have a very distant common ancestor. Sealions are more closely related to bears and seals are more closely related to otters.

• They have converged on a form. It is a co-incidence.

• Their structures are analogous to each other.

Prehistoric Convergence