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 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 Figure 21.00 The Galápagos islands are located in the Pacific Ocean, off the coast of Ecuador. Different islands in the group are ome to distinct species of marine tortoises, finches, mockingbirds, and other organisms. Darwin formulated the theory of evolution by natural selection in part to explain why closely related species are found on nearby 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 Figure: 21.2a Caption: (a) Even though their function varies, all vertebrate limbs are modifications of the same basic configuration, or basic plan. Darwin interpreted structural homologies like these as a product of descent with modification. Note that the limbs are not drawn to scale. Phalanges Turtle Human Horse Bird Bat Seal

Developmental homology Both the chick and the human have gill pouches and tails Gill pouch Figure: 21.2b Caption: (b) These photos show the strong resemblance of the early embryonic stages of a chick and a human. Tail Chick Human

Figure 21.2c ( c) Each letter in the sequences given here represents an amino acid. The sequences are from a portion of the protein products of the Aniridia gene found in humans and the eyeless gene found in Drosophilia.

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 Figure: 21.3 Caption: Present-day sloth and representation of fossil sloth. The Law of Succession: Living and fossil sloths are found only in Central America and South America. Darwin interpreted similarities among fossil and living species in the same geographic area as evidence for evolution.

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

Vestigial Traits Capuchin monkey tail Human coccyx (used for balance, locomotion) Human coccyx Figure: 21.4, left Caption: The tailbone is a human trait that is functionless. But is homologous to functioning structures in related species.

Vestigial Traits Erect hair on chimp (insulation, emotional display) Human goosebumps Figure: 21.4, right Caption: Goose bumps are human traits that are functionless. But they are homologous to functioning structures in related species.

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?