Introduction to a Darwinian View of Life Bio 204 Winter 2005 Lapsansky

Charles Darwin’s radical idea (or was it?) Meticulous observation Considered numerous possible relationships, especially b/w animals and their environment 2 main points: Species evolved from ancestral species Natural selection was the mechanism for this evolutionary change

Figure 22.1 A desire to assign order (for practical and other purposes) is at the heart of human understanding Linnaeus developed the system of binomial nomenclature

Figure 22.1 Early explanations for the great diversity of life on earth did not utilize scientific methods Darwin was trained as a natural theologian after failing medical school

Figure 22.1 Observations of some species hinted at historical connections and indicated that some change had occurred over time Transmutation (Erasmus Darwin)

Erasmus Darwin Organic life beneath the shoreless waves Was born and nurs'd in ocean's pearly caves; First forms minute, unseen by spheric glass, Move on the mud, or pierce the watery mass; These, as successive generations bloom, New powers acquire and larger limbs assume; Whence countless groups of vegetation spring, And breathing realms of fin and feet and wing. Erasmus Darwin. The Temple of Nature (This poem hints at the fact that Lamarck and Erasmus Darwin were contemporaries.)

Figure 22.1 Collecting evidence of changes affecting life on earth, over long periods of time …but was it gradual or catastrophic change?

James Hutton Scottish geologist, 1795 Geologic mechanisms are slow and continuous, producing gradual change = Geologic gradualism

Jean Baptiste Lamarck French invertebrate natural historian, 1809 Proposed that life forms evolved along with Earth’s changes used the fossil record toward greater complexity Two Principles: use / disuse inheritance of acquired characteristics How did Lamarck explain simple life forms?

Thomas Malthus English political economist, 1798 Essay on human condition as related to over- reproduction and limited resources

Georges Cuvier French anatomist, 1813 “Essay on the Theory of the Earth” and founded the science of paleontology Catastrophism, to explain earth’s history Fig 22.3

Charles Lyell Scottish geologist, 1830 Incorporated Hutton’s gradualism into this widely read book, “Principles of Geology” The same slow geologic mechanisms at work today have always been at work = Uniformitarianism Darwin concluded that the earth must be very old, and had a copy of Lyell’s book with him on the Beagle

Voyage of the Beagle

Fig 22.5 Voyage of the Beagle

Alfred Wallace British naturalist, 1858 Letter from West Indies with article to review and forward to Lyell Developed a theory of evolution identical to the one Darwin was working on

Wallace and Darwin jointly present their ideas (1858) to the Linnaean Society of London, 32 years after the end of Darwin’s voyage “On the Origin of Species” is published for the first time in 1859

On the Origin of Species Descent with modification (aka evolution) is the explanation for life’s unity and diversity all organisms are related via a common ancestor adaptations developed as descendents from a common ancestor moved into new habitats (or the habitat changed) Darwin’s metaphor for the history of life was a branching tree.

On the Origin of Species Natural selection is the mechanism 3 inferences based on 5 basic observations (as characterized by Ernst Mayr, 1982)  Too many individuals for limited resources  Those that have favorable traits are “more fit”, survive and reproduce  The traits of the survivors dominate in a population and cause it to evolve Darwin had synthesized some of the basic concepts in population ecology and inheritance, at the dawn of the Cell Theory (1839) and prior to Mendel’s genetics experiments (1866).

Observation 1 Species have a great potential for reproduction Populations would increase exponentially if all individuals survived and reproduced Fig 22.8

Observation 2 Populations tend to remain stable over time, except for mild seasonal fluctuations and occasional severe fluctuations Fig Moose population on island in Lake Superior

Observation 3 Natural resources are limited Fig Discussion in Malthus, “Essay on the Principle of Population” helped to clarify this for Darwin

Since more individuals are produced than can be supported by the available resources but population size remains stable, it means that there must be a fierce struggle for existence among individuals of a population, resulting in the survival of a part, often a very small part, of the offspring of each generation In populations, more individuals are born than can be supported by the environment Only a fraction will survive to the next generation (there is a struggle for existence) Inference 1:

Observation 4 No two individuals are exactly the same; rather, every population displays enormous variability. Fig 22.9

Observation 5 Much of this variation is heritable However, Darwin did not know the mechanism of inheritance Fig 1.3b

Inference 2: Those with better traits survive and reproduce Survival depends on an organism’s characters that are, at least in part, inherited More fit individuals will leave more offspring than less fit individuals Survival in the struggle for existence is not random but depends in part on the hereditary constitution of the surviving individuals. This unequal survival constitutes a process of natural selection.

Inference 3: Unequal ability of individuals to survive and reproduce leads to gradual change in a population More favorable characters accumulate = Microevolution (i.e. evolution in a population) Macroevolution = origin of new species and other taxonomic groups due to accumulation of change over long periods of time. Over generations this process of natural selection will lead to a continuing gradual change of populations, that is, to evolution and to the production of new species.

Peter and Rosemary Grant have been working on Galapagos finches since 1973 on Isla Daphne Major. Geospiza fortis is a seed-eater that cracks seeds by grasping at the base of the bill and applying force. Beak size is correlated with consumed seed size.

Are characteristics variable in a population? YES.

Is some of the variation among individuals heritable? YES.

Is there an excess of offspring, only some of which survive to reproduce (due to limited natural resources)? YES.

Is survival and reproduction nonrandom? YES.

Other Evidence for Evolution Organisms are adapted to their environments Camouflage is an example of evolutionary adaptation Fig 22.10a A floral mantid.

Other evidence Artificial selection Fig 22.11b Vegetables developed by humans from wild mustard plant

Other evidence Examples of natural selection over short periods of time Fig Evolution of resistance to insecticides in insect populations Is it fair to call this“natural” selection? How is it similar to antibiotic resistance among pathogenic bacteria?

Other evidence Homologous structures Fig Forearm bones in mammals

Other evidence Molecular “record” – molecular homologies Fig Ribosomal structure (large subunit of bacterial ribosome)

Other evidence Biogeography Fig Adaptive radiation of Australian marsupials compared to similarities among other mammals

Other evidence Fossil record Fossil Trilobites Fig 22.7 Elephant evolution based on fossils