III. Evolutionary thinking before Darwin. Influences on Darwin. I. Evolution and its core principles. II. The importance of evolution as a concept

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1 I. Evolution and its core principles Evolution: cumulative changes in traits of a species or population over time. Common descent with modification: The modification of species in successive generations, with such change sometimes resulting in the formation of new, separate species Natural selection: Differential success in reproduction by different phenotypes resulting from interactions with the environment Evolution occurs when natural selection produces changes in the relative frequencies of alleles in a populations gene pool. II. The importance of evolution as a concept As the organizing concept of biology Nothing in biology makes sense except in the light of evolution." Theodosius Dobzhansky As an illustration of the scientific method. As an intellectual revolution III. Evolutionary thinking before Darwin Influences on Darwin 1

2 Thales: natural phenomena by natural causes Plato: Edos essentialism Single event creation Essentialism + creationism = Natural theology Da Vinci and fossils Hutton, Lyell, and Geology Uniformitarianism: Geological forces have, and still do, mold and shape the Earth Gradualism: Geologic change is continuous, slow, and gradual, not catastrophic The earth was/is steadily undergoing change. And, if such a steady change were possible for the earth, why not for the creatures that lived on it? 2

3 Jean-Baptiste de Lamarck: French biologist, taxonomist, paleobiologist Species could change through time, changes were adaptive. Occurred through Inheritance of Acquired Characteristics: within life of an individual, changes in environment, internal needs, cause bodily changes, which offspring inherit. Lamarck believed that changes resulted from an inherent drive toward perfection. identified a line of descent: older fossils to more recent fossils to modern, living organisms ideas about the means of evolution were incorrect, but he figured out that Organisms CAN evolve One kind of organism can be ancestral to another different kind of organism 3

4 Established that further down you went, the less similar fossils were to modern forms Established fact of extinction Georges Cuvier Founder of paleontology and stratigraphy Was a catastrophist Was adamantly antievolutionary Also occurring about this time: Interest in natural history grew Worldwide exploration increased knowledge of diversity Systematic investigation of the fossil record began Geologic information grew Leeuwanhoek discovered microorganisms. IV. Charles Darwin and the theory of evolution Developed the ideas about descent with modification AND provided a large body of evidence to support them First person to perceive that natural selection is the primary force behind evolution 4

5 About Charles Born 2/12/1809, to wealthy English family of physicians. Dropped out after 2 years medical school Enrolled in divinity school, a clergyman by 1831 Spent most of his time collecting and studying nature Darwin's journey of discovery Dec joined crew of British surveying ship (HMS Beagle) Hired as the crew's naturalist to make observations and collections Darwin was 22 years old. 5

6 Post Beagle: -Returned to England 5 yrs later. -Now a mature and famous naturalist. -Married, settled down Suffered from bad health rest of life -Sorted collection, worked on notes and ideas -Never taught, participated in scientific societies, or ever left England again The evolution of the theory: A. Perceiving common descent with modification During his 5 years at sea and for a few years after his return, several observations and influences led Darwin to his ideas... From Lyell : Earth very old, still changing Geol. change slow, gradual. From fossil record: Extinctions common Relationship between age of fossil and degree of similarity to modern species Graded variation in nature: Groups of organisms can be classified based on their similarities 6

7 Geographical variation- Galapagos Islands Endemic species -the finches -the tortoises -iguanas -cacti All had mainland ancestors, but on separate islands had diverged into separate species Domestication of plants and animals artificial selection could significantly alter the traits of a species Thomas Malthus wrote Essay on the Principle of Population human populations increase geometrically food production increases arithmetically human population size increases to point: - intense competition for limited resources -poverty, overcrowding, war, famine, disease From this Darwin envisions "struggle for existence" as applied to species other than human beings. 7

8 B. Perceiving natural selection Development of the natural selection theory is based on three inferences that are drawn from five facts: Fact 1: All species have the potential for exponential pop. growth. Fact 2: Pop. size generally remains stable. Fact 3: Resources are limited. Inference 1: Since more individuals are produced than can be sustained by available resources, there must be an intense struggle for existence among individuals of a population, resulting in the survival of only a small portion of each generation. Fact 4: No two individuals are exactly the same. Fact 5: Most of this individual variation is heritable. Inference 2: Survival is not random; depends on genetic constitution of the individual; differential survival is the process of natural selection. Inference 3: Over many generations, natural selection will cause a gradual change in populations. 8

9 Alfred Russel Wallace Sent essay to Darwin outlining almost exactly the ideas Darwin had in his own theory of evolution. 1858, both men s essays presented at meeting in London. Both men formally received equal credit for the idea of evolution by natural selection. 1859, Darwin published On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. The theory of evolution is really a set of related ideas: Descent with modification species change over time Natural selection is the mechanism there are differences in reproduction and survival among individuals due to genetically inherited traits. Gradualism species evolve gradually through steady accumulation of changes, rather than abrupt/drastic changes. Radiometric dating Technique used to date rocks Compares proportion of a radioactive element to its nonradioactive decay product, Time calculated using uniform rate at which decay occurs. With this technique, fossil layers can be dated to determine when the plants and animals in those layers lived. 9

10 The placement of fossils Fossils appear in layers (strata) Position of fossils in the strata reveals their relative age Fossils are distributed consistently Fossils show linkages between ancestral forms to more recent ones via intermediate forms Biogeography Study of species geographical distributions (past and present). Geographic distribution of organisms reveals relationships Example: The Galapagos Islands species 10

11 Comparative Anatomy : the the comparison of body structures in different species Common descent evident in anatomical similarities between species Homologous structures Vestigial structures Homologous structures Vestigial structures 11

12 Unrelated species in similar environments have evolved similar forms: Convergent evolution Analogous structures Homology indicates ancestry, analogy does not Comparative Embryology: Closely related organisms pass through very similar stages during embryonic development. Example: all vertebrate embryos pass through a stage in which they have openings called gill pouches on the sides of their throats, which develop into different adult structures 12

13 Comparative Molecular Biology Common set of molecular machinery for all cells: amino acids, nucleotides, ATP, genetic code Comparisons of amino acid or nucleotide sequences among species, allow construction of hierarchies of relatedness. The greater the similarities, the more closely related two species are Example: hemoglobin in various species Artificial Selection By choosing which individuals of a population will breed and which will not, humans have altered the traits of populations of plants and animals for thousands of years. This is Artificial not Natural Selection Experimental evidence In the lab, can alter selection pressures: (change temperature, predators, food source, etc.) and can alter gene frequencies in a population over successive generations And by mistake--antibiotic resistance 13