Evolution Nothing in biology makes sense except in
Evolution Nothing in biology makes sense except in the light of evolution. – Theodosius Dobzhansky Charles Darwin in later years
What is Evolution? The kind we’re talking about is sometimes called organic evolution to distinguish it from non-biological changes over time. Working definition: Evolution is the progressive change in organisms over time.
Evolution Holds a Unique Place in Biology Other disciplines ask how? Evolutionary biology asks why?
Evolution’s Core Principles Common descent with modification.
Evolution’s Core Principles Natural selection.
Darwin’s Voyage of Discovery A reconstruction of the HMS Beagle sailing off Patagonia.
The Voyage of the Beagle
Darwin’s Ideas Did Not Develop in a Vacuum Contributor’s to Darwin’s thinking included: Charles Lyell – uniformatarianism. Georges Cuvier – species extinction. Thomas Malthus – struggle for existence. Jean Baptiste de Lamarck – evolution by acquired characteristics.
Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck n Theory had three major parts 1) 2) 3) Use and disuse Theory of need Inheritance of acquired characteristics Summary-organisms would pass on a trait to their offspring to better adapt to the environment. *Lamarck had no experimental data*
August Weismann n n Challenged and disproved Lamarck. Cut off the tails of mice for 21 generations. Results-tails would always show up in the offspring. Conclusion-Lamarck’s theory was wrong.
Alfred Russel Wallace Independently Drew the Same Conclusions as Darwin Papers from Wallace and Darwin were jointly presented (with little impact) to the Linnaean Society in 1858.
Darwin’s Observations and Inferences Observation 1: Left unchecked, the number of organisms of each species will increase exponentially, generation to generation. Observation 2: In nature, populations tend to remain stable in size. Observation 3: Environmental resources are limited. Inference 1: Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals, with only a fraction of offspring surviving each generation.
Darwin’s Observations and Inferences Observation 4: Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike. Observation 5: Much of this variation between individuals is heritable.
Darwin’s Observations and Inferences Inference 2: Survival in the struggle for existence is not random, but depends in part on the heritable characteristics of individuals. Individuals who inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals.
Darwin’s Observations and Inferences Inference 3: The unequal ability of individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations (natural selection). These three inferences are a statement of Darwin’s Theory of Evolution.
The Weak Link of Genetics and the Modern Synthesis A major problem in Darwin’s theory was the lack of a mechanism to explain natural selection. How could favorable variations be transmitted to later generations? With the rediscovery of Mendel’s work and its vast extension in the first half of the 20 th century, the missing link in evolutionary theory was forged. Darwin in his early years. Darwinian theory supported by genetics is known as the modern synthesis.
Adaptation n n An inherited variation that increases an organism’s chance of survival in a particular environment. 1) Mimicry- a structural adaptation that provides protection for an organism by copying the appearance of another species.
Adaptation n Camouflage-A structural adaptation that enables an organism to blend in with its surroundings.
Adaptation n n Physiological adaptations- are changes in an organism’s metabolic processes. Ex. Camel- adaptation to heat and dryness.
Opposition to Evolution The upheaval surrounding evolution began with publication of On the Origin of Species and continues nearly 150 years later. Two (of many) arguments made against evolution are: Evolution is only a theory. No one’s ever seen evolution. Both arguments are easily countered. An early disparaging view of evolutionary theory and its creator.
Evidence for Evolution – The Fossil Record
Evidence for Evolution - Comparative Morphology Homologous Structure- A modified structure that is seen among different groups Of descendants.
Evidence for Evolution - Comparative Embryology Why do embryos of different animals pass through a similar developmental stage? This one has been disproved as technology has enabled scientists to look into the Wombs of parent organisms to see developing embryos. The structure that looks like A tail is the spine which develops quickly and the rest of the body has to catch up.
Evidence for Evolution n Analogous structureany body structure that is similar in function but different in structure.
Evidence for Evolution n n Vestigial structure. Any body structure that is reduced in function in a living organism but may have been used in an ancestor. Ex. Appendix, hip bone in whales.
Evidence of Evolution – Genetic Conservation and Diversification Why should different organism possess related genes? Why does the degree of relationship of genes relate perfectly to their degree of relationship established by other methods?
n n Many seemingly simple or less developed organisms have many more genes then humans which are considered the most complex or developed. We only have 23 pairs, or 46. A horse has twice as many.
Evidence for Evolution – Evolution Observed Evolution of pesticide resistance in response to selection.
Evidence for Evolution – Evolution Observed Evolution of drug-resistance in HIV.
Evidence for Evolution – Evolution Observed Selection against small guppies results in an increase in average size.
Evolutionary Time Scales Macroevolution: Long time scale events that create and destroy species.
Evolutionary Time Scales Microevolution: Short time scale events (generation-to-generation) that change the genotypes and phenotypes of populations.
Species n n Reminder- a species is a group of organisms distinct from all other organisms and capable of interbreeding with others of its kind. Speciation- the evolution of new species can occur only when either interbreeding or the production of fertile offspring is somehow prevented.
Mechanisms of Speciation n n 1) Variation 2) Migration 3)Environmental change 4) Selection 5) Isolation
Natural Selection leading to a new species n n n Adaptive radiation- when many related species evolve from a single ancestral species. It will most commonly occur when a species of organisms successfully invades an isolated region where few competing species exist. Also called divergent evolutionwhere two or more similar species become more and more dissimilar.
Convergent evolution n n When unrelated species become more and more similar in appearance as they adapt to the same kind of environment. Example- cactus in US and Africa
Co evolution n n The joint change of two or more species in close interaction. A predator a their prey can coevolve. Parasites and their host can also coevolve.
Natural Selection n 1) Stabilizing-favors average individuals 2) Directional-favors the one extreme 3)Disruptive-favors both extreme
Equilibrium n n n A population that is in genetic equilibrium, no genetic change from generation to generation. For a population to evolve there must be a disturbance in its genetic traits. Any factor that can affect genes can affect equilibrium of genetic traits. One such factor can be mutation.
Mutations n n Caused by factors in the environment: such as radiation or chemicals, others are purely by chance. They are very important to evolution because they add new genetic material to a population. Most are harmful, a very few can benefit a population.
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