Evolution
(Darwin and Darwinism)
The History of An Idea
Darwin’s Theory
A Darwinian View of Life
Human 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
Inheritance of Acquired
Characteristics - 1802
Essay on the Principle of
Populations - 1798
Jean-Baptiste Lamarck
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
Humerus
Radius and ulna
Carpals
Metacarpals
Phalanges
Turtle
Human
Horse
Bird
Bat
Seal
Developmental homology
Both the chick and
the human have gill
pouches and tails
Gill pouch
Tail
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
The Law of Succession
Present-day sloth
Fossil sloth
Extinctions
Fossils of trilobites, animals that lived in the seas hundreds of millions of
years ago
Vestigial Traits
Human coccyx
Capuchin monkey tail
(used for balance, locomotion)
Vestigial Traits
Human goosebumps
Erect hair on chimp
(insulation, emotional display)
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?