Charles Robert Darwin 1809 1882 Charles Darwin and

Charles Robert Darwin (1809 -1882)

Charles Darwin and the Voyage of the Beagle

Charles Darwin and the Voyage of the Beagle • During the voyage, Darwin. . . – – was perennially seasick read Lyell’s “Principles of Geology” spent lots of time ashore in South America and other locations observed and collected a large number of fossils, plants, and animals • What Darwin Saw. . . – an earthquake that changed the level of the land dramatically in Concepcion, Chile… – fossils of marine shells at 14, 000 feet in the Andes… – patterns of geographic distribution of plants and animals that suggested the importance of geographic isolation in the formation of species. . .

Charles Darwin and the Voyage of the Beagle • What Darwin Saw: • Plants and animals in the New World tropics are like those in the New World temperate zone, not like those in the Old World tropics. • Extant South American plants and animals are like extinct South American plants and animals, not like extant plants and animals elsewhere. • Extant mammals in Australia are not like mammals anywhere else. • Animals (and plants) on oceanic islands are like those of the nearest continent, not like those on other oceanic islands elsewhere. • Animals on islands near each other in archipelagoes are distinct but similar.

Charles Darwin and Natural Selection • Darwin wrote two essays, the first in 1842, and an expanded version in 1844 • The 1844 “essay” (it was 240 pages) contains a complete, detailed, and well documented argument for how the process of natural selection acts to produce adaptation or “design” in organic beings • Darwin knew what he had done, and showed none but his wife and a few close colleagues his essay. . .

Darwin in 1854

Charles Darwin and Natural Selection “We see these beautiful co-adaptations most plainly in the woodpecker and misseltoe; and only a little less plainly in the humblest parasite that clings to the hairs of a quadruped or the feathers of a bird; in the structure of the beetle which dives through the water; in the plumed seed which is wafted by the gentlest breeze; in short, we see beautiful adaptations everywhere…” Darwin, 1859

Charles Darwin and Natural Selection "How have all those exquisite adaptations of one part of the organisation to another part, and to the conditions of life, and of one distinct organic being to another being, been perfected? " Darwin, 1859

Charles Darwin and Natural Selection • Ernst Mayr (1904 -2004): – Eminent naturalist – Architect of the “new synthesis” – Analyzed Darwin’s argument in “On the Origin of Species” – A Mayr quote: “Being a biologist is such great fun!”

Natural Selection • Fact 1: Many more organisms are produced through reproduction than can survive (geometric increase, biotic potential) – The principle of Malthus

Natural Selection • Fact 1: Many more organisms are produced through reproduction than can survive (geometric increase, biotic potential) – Cockroaches, rabbits, cattails – Elephants – People?

Natural Selection • Fact 1: Many more organisms are produced through reproduction than can survive • Fact 2: Population sizes of most species are stable on a seasonal and annual basis (in spite of biotic potential, population sizes do not increase)

Natural Selection • Fact 1: Many more organisms are produced through reproduction than can survive • Fact 2: Population sizes of most species are stable on a seasonal and annual basis • Fact 3: Natural checks on increase…

Natural Selection • Fact 1: Many more organisms are produced through reproduction than can survive • Fact 2: Population sizes of most species are stable on a seasonal and annual basis • Fact 3: Natural checks on increase: limitation of resources, predation, abiotic conditions

Natural Selection • Fact 1: Many more organisms are produced through reproduction than can survive • Fact 2: Population sizes of most species are stable on a seasonal and annual basis • Fact 3: Natural checks on increase • Inference 1: A struggle for existence…

Natural Selection “Two canine animals in a time of dearth, may be truly said to struggle with each other which shall get food and live. But a plant on the edge of the desert is said to struggle for life against the drought… The misseltoe is dependent on apple and other trees, but can only in a far-fetched sense be said to struggle with these trees. . . ” Darwin, 1859

Natural Selection “…I use the term Struggle for Existence in a large and metaphorical sense, including dependence of one being on another, and including…not only the life of the individual, but success in leaving progeny. ” Darwin, 1859

Natural Selection • Fact 4: Variation in characteristics among individuals within populations of organic beings

Natural Selection The granite grasshopper, Trimerotropis saxatilis

Natural Selection • Fact 4: Variation • Fact 5: Heritability - characteristics are passed from parents to offspring

Natural Selection • Fact 4: Variation • Fact 5: Heritability

Natural Selection Francis Crick and James Watson elucidate the structure of DNA - 1953

Natural Selection • Fact 4: Variation • Fact 5: Heritability • Inference 2: Differential Reproductive Success - because of their characteristics, some individuals are more likely to survive and produce offspring than others – “Can we doubt. . . that individuals having any advantage, however slight, over others, would have the best chance of surviving and procreating their kind? ” Darwin, 1859

Natural Selection Plectrodera scalator Stenaspis verticalis

Natural Selection • Fact 4: Variation • Fact 5: Heritability • Inference 2: Differential Reproductive Success • Inference 3: Successful characteristics (those that promote individual survival and reproductive success) become more prevalent in the population (the characteristics of the population are modified through descent)

Natural Selection • • Fact 4: Variation Fact 5: Heritability Inference 2: Differential Reproductive Success Inference 3: Successful characteristics become more prevalent in the population • Darwin's conclusion: Over time, various changes accumulate in populations, leading to well adapted or designed organisms

Natural Selection • Individuals differ in various phenotypic characteristics • Phenotypic characteristics of individuals can be passed to their offspring • Some individuals produce more offspring than others (because of their characteristics) • Phenotypic characteristics that confer greater reproductive success become more prevalent in the population • Changes accumulate in the population over time • Accumulated changes in characteristics lead to better designed or adapted organisms

Natural Selection The “Darwinian Mantra” • • • Variation Heritability Differential Reproductive success Spread of traits through the population Accumulation of change over time Changes in characteristics lead to better designed or adapted organisms

Natural Selection The “Darwinian Mantra” Heritable variation combined with differential reproductive success leads to the spread of traits through populations, which leads to adaptation.

Natural Selection “Survival of the fittest”?

Types of evolutionary change • Anagenesis • Cladogenesis • AKA Microevolution • AKA Macroevolution • adaptive change within • derivation of new species from previously existing • “descent with ones modification” • “transmutation of species”

Natural Selection in Action industrial melanism Biston betularia, the Peppered moth Typical form Biston betularia, the Peppered moth Melanic form

Natural Selection in Action Biston betularia A mark-recapture experiment: marked melanic and typical moths were released onto polluted and clean tree trunks, then recaptured later. The data (% recaptured): polluted trees clean trees melanics 34. 1% 6. 3% typicals 16. 0% 12. 5%

Natural Selection in Action Biston betularia Direct observations of predation: melanic and typical moths were placed onto polluted and clean tree trunks, then observed from a blind. The data (% attacked by birds): polluted trees clean trees melanics 26% 86% typicals 74% 14%

Natural Selection in Action Biston betularia • Criticisms of the “industrial melanism”story: • Melanism is environmentally induced • It can be, but… • Moths don’t actually rest by day on tree trunks • They do, but not exclusively • Kettlewell glued his moths to the tree trunks • What else was he to do?

Natural Selection in Action Biston betularia • Criticisms of the “industrial melanism”story: • Changes in frequency of melanics and typicals doesn’t match changes in lichen cover of tree trunks • In Great Britain… • In the US… • The bottom line on Industrial Melanism…