Principles of Evolution Chapter 10-11 Principles of Evolution

Early evolutionary scientists Carolus Linnaeus (Sweden) 1700s – developed a classification system; proposed new organisms come about through hybridization Georges-Louis Leclerc de Buffon (France) 1700s – proposed that species shared ancestors and did not arise independently; suggested Earth was much older than 6000 years

Early evolutionary scientists Erasmus Darwin (England) 1700s- proposed that all living things descended from a common ancestor; more complex forms come from less complex forms Jean-Baptiste Lamarck (France) 1800s- organisms evolved toward perfection and complexity; species don’t go extinct, they evolve into other forms; believed in acquired characteristics

Theories of geologic change Georges Cuvier (France)- theory of catastrophism: natural disasters shaped landforms and helped species become extinct; new species would move into the area James Hutton (Scotland) – theory of gradualism: changes in landforms occur over long periods of time

Theories of geologic change Charles Lyell (England) – published “Principles of Geology”; theory of uniformitarianism: processes that shape Earth are uniform through time; Earth changes gradually but at a constant rate

Darwin’s studies on the HMS Beagle 5 year collecting, mapping expedition to the South Pacific Darwin’s collections helped him develop his evolutionary theory

Darwin’s studies in the Galapagos Islands Most important observations Studied and compared anatomy of species of reptiles, insects, birds, and flowering plants that were similar to those in other parts of the world Studied fossils and found there were resemblances to modern organisms Experienced earthquakes that pushed land up above sea level; geologic processes

Darwin’s studies in the Galapagos Islands

Darwin completes studies in England Darwin found that all life struggles for existence All life competes for food, space, shelter Must escape predators Only some live long enough to reproduce Found different variations of traits in organisms of the same species

Darwin explanation for evolution Artificial selection- technique in which breeders select particular traits that will be seen in offspring Natural selection (Darwin’s theory)- mechanism for change in populations that occurs when organisms with favorable variations for a particular environment survive, reproduce, and pass these traits on to the next generation Each new generation is made up of organisms with the most favorable characteristics.

Natural Selection: 4 principles Variation-heritable differences are the basis; result from genetic material Overproduction-many offspring ensure that some will survive but causes competition among them Adaptation-characteristic that gives an individual a better chance at survival; better chance at producing offspring Descent with modification-over time, more individuals will have more of the “best” characteristics that allow them to survive and reproduce

Fitness Part of the natural selection process Fitness- a measure of the ability to survive and produce more offspring relative to other members in the population

Adaptations can be compromises Not all adaptations make the organisms perfectly suited to its environment Ex: the Panda’s “thumb” is a wrist bone with a thumb-like function, used to hold bamboo

Evidence for evolution A. Fossils Provide a record of earlier life Is incomplete but provide evidence of evolution Can show step by step sequence of evolution for some species

Evidence continued B. Anatomical studies Viewing basic limb (skeletal) structure can indicate a common ancestor Different species often exhibit homologous structures ( modified body parts that are similar in structure, function, or both) Analogous structures have similar functions but different structures and cannot be used to indicate evolutionary relationships

Evidence continued C. Functionless structures Vestigial structures are reduced in function in modern organisms but may have been used by an ancestor Continue to be inherited without function Ex. Human appendix, ostrich wings, eyes in sightless species

Evidence Continued Embryological development Similarities in embryological parts Tail, gill slits present in all species Become distinct only as development continues

Evidence continue E. genetic comparisons More reliable than anatomical studies Comparisons of DNA and RNA

Population genetics Populations evolve; individuals don’t Can use genotypes of individuals in a population to calculate allelic frequency (% of an allele in the gene pool) Populations are in genetic equilibrium when allelic frequencies remain unchanged

Populations genetics cont. B. Changing genetic equilibrium leads to evolution Anything that can disrupt or change an allelic frequency can lead to evolution Mutations Genetic drift: alteration of allelic frequency by chance (small populations) Movement of individuals in and out of population (genes are gained or lost)

Population genetics cont. C. Natural selection Individuals more likely to survive and pass their genes on to the next generation Allelic frequencies change from one generation to the next Three types of natural selection 1.stabilizing-favors average individuals 2.directional-one extreme form of a trait is favored 3.disruptive-favors two extreme forms of a trait

Types of selection

Evolution vs. genetic equilibrium 1908 – Hardy-Weinberg Principle states that allele frequencies in a population will remain constant unless some factor causes the frequencies to change. 5 conditions to maintain genetic equilibrium Random mating Very large population No immigration or emigration No mutations No natural selection

Evolution occurs If all 5 conditions of Hardy-Weinberg are NOT met Any change in the gene pool will result in the evolution of the population

Evolution of species speciation-evolution of a NEW species can occur only when either interbreeding or the production of fertile offspring is prevented

Isolating mechanisms that can result in speciation Geographic isolation Behavioral isolation Temporal isolation

Geographic isolation Physical barriers can prevent interbreeding Precipitation Volcanic eruptions Sea-level changes 1.changes mating behavior 2.changes chromosome number (polyploidy)

Behavioral isolation Differences in courtship rituals or other reproductive strategies that involve behavior If behaviors are not recognized, females will not accept mates

Temporal isolation 2 or more species reproduce at different times If timing of courtship or release of gametes (sea animals or plants) is not specific, mates are not accepted by females (animals), or fertilization does not occur (sea animals and plants)

Patterns of evolution Species diversify when introduced to new environments (adaptive radiation) Divergent evolution pattern in which species that were all similar to the ancestral species become more distinct 1.different environments 2.different climates C. Convergent evolution- the pattern of evolution in which distantly related organisms evolve similar traits 1.occupy similar environments 2.similar selection pressures