Chapter 1 Opener A plethora of adaptations

Figure 1.3 (A) Lamarck’s theory of organic progression. (B) Darwin’s theory of descent, with modification, represented by a phylogenetic tree

Figure 1.3 (A) Lamarck’s theory of organic progression. (B) Darwin’s theory of descent, with modification, represented by a phylogenetic tree

Figure 1.4 Transformational and variational theories of evolutionary change across three generations

Platonic Idealism

Plato (428 – 348 BC)

– Observable world is only a shadow of underlying "ideals"

– Species (ideals) are fixed and eternal

Species Concepts - AristotleAristotle (384-322 BC)

– Adult form explains changes that occur in immature (embryonic) forms.

– Teleological (goal oriented) explanation of species

– Scale of Nature

• Species arranged from least perfect to most perfect

Fig 1.2 pg 8

Species Concepts - The Great Chain of Being

Derived from Aristotle's Scale of Nature

Johann von Goethe (1749-1832)

– Archetype, or Bauplan

• Unique fundamental plan that defined each level of the scale of nature

• Example: The stem, root and flower of plants founded from ancestral plant that had only one main organ, the leaf.

Fig 1.3 pg 9

Classification of Species

Carl Linnaeus (1707-78)

– Binomial nomenclature: genus & specific epithet

– Still believed in species constancy, dismissing evolutionary transformation

Uniformitarism

– Alternative interpretation that did not require catastrophes to explain fossil record

– Gaps are absent if geology examined over large area

– Changes in geology due to same phenomena that occur today:

• erosion from rain and wind

• volcanism and flood deposition

– Earth is very old, for such changes to have occurred.

Evolution

– From Latin evolutio, unrolling

– 17th century : unfolding of the parts of the embryo, or organs, to reveal adult body plan

– Now refers to transformation of a features or species through time.

Charles Darwin (1809-1882)

– An avid hunter, with strong interests in collecting, geology and botany.

– At age of 16 began to study medicine, later switched to study theology at Cambridge University

• He did not finish.

– In 1831, became the naturalist onboard the ship H.M.S Beagle, during a five-year voyage of geographical exploration.

Fig 2.1 pg 21

Figure 2.02a: H.M.S. Beagle

© SPL/Photo Researchers, Inc.

Voyage of the Beagle

– Darwin read Lyell's Principles of Geology, and used it to study geological features during the voyage.

– Discovered fossil bones in Argentina, such as the 6m-high giant sloth, Megatherium.

Fig 2.3 pg 24

Galapagos Islands

– Small volcanic islands off western coast of South America.

– Darwin collected many specimens of finch.

• He later noted that each island had finches with a unique beak shape.

Fig 2.4 pg 25

Darwin's Finches

– Each island has unique beak shape.

– Darwin noted that the variation in beak shape provided advantages for the food source available on each island.

– Beak shape modified, but how?

• Natural Selection

Fig 2.5 pg 26

Lamarckian Inheritance

Lamarckism – adaptations driven by an inner vital force.

Principle of Use and Disuse Variation– When a feature is used, it becomes elaborated, and

when it is not used it regresses.

– Proposed as means for variation among species, and development of adaptations.

Inheritance of Acquired Characters– Adults pass on traits by somehow passing on somatic

cells.

Natural Selection

Thomas Malthus (1766-1834)

– Wrote a short paper about population growth and food sources.

• Populations grow geometrically (2, 4, 8,…)

• Food Sources grow arithmetically (1, 2, 3,…)

• Leads to food shortage

Darwin realized food shortage acted as selection force, driving variation among species.

Table 1.01: A few of the major figures whose contributions in the nineteenth century or earlier influenced evolutionary concepts

Embryology

Early 19th century studies of ontogeny (development of the individual) demonstrated early embryos look very similar.

Fig 3.14b pg 51

Embryology

Ernst Haekel (1834- 1919)

– Biogenetic law: Stages in the development of an individual (ontogeny) recapitulate the evolutionary history (phylogeny) of the organism.

– Incorrectly believed early stages represented previous adult forms.

Haeckel's classic illustration of different vertebrate embryos at comparable stages of development

Fig 3.14a pg 51

Figure 3.17: The process of fossilization

Adapted from Kardong, K.V. Vertebrates, 2nd ed. WCB/McGraw-Hill, 1998.

Fossils

Fossils demonstrate that evolutionary changes do not occur in a single line (orthogenesis), but rather result in a "bushy" family tree.

Fig 3.19 pg 56

Artificial Selection

– Selective breeding of parents with desirable traits, and cull (destruction) of the offspring with undesirable traits.

– Evidence used extensively by Darwin

Fig 3.22 pg 59

Natural Selection

Darwin's view of evolution, similar to artificial selection but not involving human intervention.

– Chance events arise, variation

– Selection occurs

– New adaptations arise over generations

Figure 1.PR01: Ernst Mayr

© Kris Snibbe/Harvard University News Office

Neo-DarwinismThe Modern Synthesis

T. Dobzhansky 1937. Genetics and the Origin of Species

E. Mayr 1942. Systematics and the Origin of Species

G. G. Simpson 1944. Tempo and Mode of Evolution

R. A. Fisher 1930. The Genetical Theory of Natural Selection

S. Wright 1931. Evolution in Mendelian Populations

J. B. S. Haldane 1932. The Causes of Evolution

J. Huxley 1942. Evolution: The Modern Synthesis

G. L. Stebbins 1950. Variation and Evolution in Plants

Reconciled Darwinian Evolution with Mendelian Genetics