Nothing in biology makes sense except in the light of evolution. Theodosius Dobzhansky Evolution Charles Darwin in later years What is Evolution? The kind were 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? Evolutions Core Principles Natural selection. Common descent with modification. Darwins Voyage of Discovery The Voyage of the Beagle Darwins Ideas Did Not Develop in a Vacuum Contributors to Darwins thinking : Charles Lyell: uniformatarianism - the assumption that the natural processes operating in the past are the same as those acting today Georges Cuvier demonstrated species extinction using the fossil record Thomas Malthus noted the struggle for existence in biological populations Jean Baptiste de Lamarck proposed evolution by acquired characteristics Alfred Russell Wallace independently drew the same conclusions as Darwin Papers from both Wallace and Darwin were jointly presented to the Linnaean Society in They were greeted by silence. Darwins Observations and Inferences Observation 1: Left unchecked, the number of organisms of each species will increase exponentially from generation to generation. Observation 2: In nature, populations tend to remain stable in size. 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 in each generation. Observation 3: Environmental resources are limited. Darwins 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 based characteristics passed on from the parents. 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. Darwins Observations and Inferences Inference 3: The inability of some individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations. This is natural selection. Darwins Observations and Inferences The Weak Link of Genetics and the Modern Synthesis A major problem in Darwins theory was the lack of a mechanism to explain natural selection. How could favorable variations be transmitted to later generations? Mendels work and its vast extension was rediscovered in the first half of the 20th century. The missing link in evolutionary theory was found. Darwinian theory supported by genetics is known as the modern synthesis. The D Train in his early years. Discomfort With Evolution A disparaging early view of evolutionary theory and its creator. The upheaval surrounding evolution began with publication of On the Origin of Species and continues over 150 years later. 1925 November, 2005 December, 2005 Two of many arguments made against evolution are: Evolution is only a theory. No ones ever seen evolution. The first point is true, but misses the meaning of scientific theory, and the second point is easily countered. Evidence for Evolution The Fossil Record Evidence for Evolution - Comparative Morphology Why use the same skeletal plan for these very different appendages? Evidence for Evolution - Comparative Embryology Why do embryos of different animals pass through a similar developmental stage? Recent discoveries of the conservation of molecular mechanisms of development are even more compelling. Evidence of Evolution Conservation and Diversification at the Molecular Level Why should different organism possess related genes? Why does the degree of relationship of genes match their degree of relationship established by other methods? Evidence for Evolution Evolution Observed Evolution of pesticide resistance in response to natural selection.
