Evolution(Darwin and Darwinism)

The History of An IdeaDarwin’s Theory

A Darwinian View of LifeHuman Evolution

The historical context of Darwin’s life and ideas

Fossils of trilobites, animals that lived in the seas of long ago

Gradualism (Hutton) – ex. Strata of sedimentary rock at the Grand Canyon

Ideas that shaped Darwin’s worldview

Jean-Baptiste Lamarck

Inheritance of Acquired Characteristics - 1802

Essay on the Principle of Populations - 1798

Thomas Robert Malthus

Formation of sedimentary rock and deposition of fossils from different time periods

Cuvier (early 1800s) - paleontology: the history of life recorded in rock strata

Excavation of British Canal system and roadways

Ideas that shaped Darwin’s worldview – Animal husbandry

“Polly”

Charles Darwin in 1859, the year The Origin of Species was published

The Voyage of HMS Beagle 1831-1836

Galapagos Islands

Galápagos finches

Diversification of finches on the Galápagos Islands

The Origin of Species

• Descent with Modification (evolution)– unity of life– all organisms related through a distant ancestor

• Natural Selection and Adaptation– the mechanism of evolution– capacity for “overproduction” of offspring– a struggle for survival– variability in population favors some individuals over

others

Descent with modification

Overproduction of offspring

A few of the color variations in a population of Asian lady beetles

Camouflage as an example of evolutionary adaptation

Artificial selection: cattle breeders of ancient Africa

A Darwinian View of Life(Darwin’s main ideas)

• Natural selection is differential success in reproduction

• Natural selection occurs through an interaction between the environment and the inherent variability among the individuals making up a population

• The product of natural selection is the adaptation of populations to their environment

Evidence for Evolution

• Evidence that Species are Related– Geographic proximity of similar but distinct species. – Homologies: structural, developmental, and

genetic.

Structural homology

Turtle Human Horse Bird Bat Seal

Humerus

Radius and ulna

Carpals

Metacarpals

Phalanges

Developmental homology

Gill pouch

Tail

Both the chick andthe human have gillpouches and tails

Chick Human

Evidence for Evolution – Darwin’s Predictions

• Evidence that Species Change over Time:– Law of succession

• In a given geographic region, species are succeeded by similar species

– Evidence of extinctions in the fossil record– Vestigial traits

Present-day sloth Fossil sloth

The Law of Succession

Extinctions

Fossils of trilobites, animals that lived in the seas hundreds of millions of years ago

Human coccyxCapuchin monkey tail(used for balance, locomotion)

Vestigial Traits

Human goosebumpsErect hair on chimp(insulation, emotional display)

Vestigial Traits

A phylogenetic tree of primates

Darwin as an ape - Public reception of Darwin ideas

Apes - our closest relatives: Gibbon , orangutan, gorilla, chimpanzee

A timeline for some hominid species

Major Features of Human Evolution

• Enlarged Brain Size– 450 cm3 (Homonoids 6 my) 1300 cm3 (Modern Humans)

• Jaw Shape– Prognathic jaw (flattened face)

• Bipedal Posture– Adaptation to non-arboreal lifestyle

• Reduced Sexual Dimorphism– males ~ 1.2 times female body size

• Changes in Social Structure– pair bonding, increased parental care

Upright posture predates an enlarged brain in human evolution

Lucy - 3.2 mya

Turkana boy - Homo habilis 1.7 mya

Two hypotheses for the origin of anatomically modern humans

Clock analogy for some key events in evolutionary history

Challenges to the understanding of evolution:•Chance•Contingency•Deep time•Extinctions•Continuity of process

Conclusion of “On the Origin of Species”

“There is grandeur in this view of life, with its several powers,

having been originally breathed (by the Creator) into a few

forms or into one; and that, whilst this planet has gone cycling

on according to the fixed law of gravity, from so simple a

beginning endless forms most beautiful and most wonderful

have been, and are being, evolved.”

- Charles Darwin, 1859

Questions?

1) How does the idea that evolution is a continuous process, happening all around us all the time, rather than some remote process that happened long ago, influence the way you think about life on Earth? 

2) Of the various challenges to a conceptual understanding of evolutionary theory (i.e. the role of random chance, contingency, vast stretches of time, Earth’s long history of extinctions, the process of natural selection, etc.) what gives you the most difficulty intellectually.

3) Over the years, a variety of Creationistic “alternatives” to evolution have surfaced in the popular media. This has included “scientific creationism” in the 1980s and most recently “intelligent design.” Why is the general public often quick to embrace these ideas and why have they been quickly rejected by the scientific community?