what is evolution

Evolution “Nothing in biology makes sense except in light of evolution” -T. Dobzhansky why? 1. 2. Examples of things that evolutionary biology helps explain:   universal genetic code similarity of mammalian forelimbs What is the biological explanation for these two things?  The unusual distribution of species Why are there so many species of finches on the Galápagos and so few other species that might be expected to do well there? History of Evolutionary Thought Aristotle What is his “scale of nature?” 1 Early Christianity What was natural theology? A changing world view a) b) Discovery of New lands Astronomy What did Copernicus & Galileo propose and why did the Church object? c) Industrial Revolution Geology – especially the acceptance of an old Earth d) e) Biology– especially the realization that the number of species was enormous Paleontology –change over time, extinct species f) Early Evolutionists Carolus Linnaeus (1707-1778) What was his most important contribution? 2 Jean Baptiste Lamarck (1744-1829) Charles Darwin (1809-1892) • 1831 (22 years old) - 5 year voyage on Beagle • 1844 (35 yrs) - 1st essay on natural selection • 1858 (49 yrs) - letter from Wallace Alfred Russel Wallace (1823-1913) 1859 - “On the Origin of Species by Means of Natural Selection or the preservation of Favoured Races in the Struggle for Life” What were the two major themes of Darwin’s book? The Theory of Natural Selection A. More individuals are produced in a population than can possibly survive to reproduce 3 B. There is heritable variation within every population C. Survival and reproduction is not random What does this mean? D. The closing paragraph of The Origin: There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved. - Charles Darwin What Darwin did not know:   4 These gaps were largely filled in by the “Modern Synthesis” (1930’s – 1940’s) integration of genetics and evolutionary theory Evolution Today Evolutionary Biology continues to be an active area of scientific research - number of research articles dealing with evolution in one year (1997) = _________ Percentage of the general public that thinks life evolved: ___________ Percentage of Biologists and Geologists that think live evolved: _________ Possible reasons for this discrepancy • Distaste for the idea that humans are related to animals • Science is incompatible with the literal interpretation of creation stories • Creationists have successfully convinced the public that evolution is bad science What Creationists Say  "Evolutionists believe that living things evolved by chance." What biologists say:  "Evolution predicts intermediate forms and there are none." What biologists say:  "Evolution is just a theory." This argument works because most people think … This latter idea appeals to our democratic sensibilities, but is irrational. Science is based on the principle that theories can be tested and if two theories conflict it is possible to discover which is a better explanation of nature. To say that we cannot do so is to say that we are doomed to live in ignorance. When Copernicus suggested that the earth went around the sun that was a theory. Eventually the evidence became so convincing that scientists considered the matter finally settled. 5 What biologists say:  "Evolutionary theory does not allow for a Creator" What do biologists say? “… new knowledge has led to the recognition in the theory of evolution of more than a hypothesis. …the result of work that was conducted independently is in itself a significant argument in favor of this theory.” John Paul II, 22 October 1996 Evidence for Historical Evolution 1. Fossil Record - provides direct evidence for historical evolution How old is the Earth? How old is the earliest known fossil? a. shows evolutionary sequence b. Transitional Forms examples? 2. Comparison of living species a. anatomical comparisons 6 b. molecular comparisons  universal genetic code what is this and how does it provide evidence for historical evolution (it has been covered in previous lectures and in the book)?  similarity of DNA and protein sequences Differences in DNA can be used as an “evolutionary clock” 3. Vestigial Structures define How do vestigial structures provide evidence for historical evolution?   7 4. Distribution of species What are usual characteristics of the species found on volcanic islands    This suggests that island species arise by…. 5. Observation of evolution in action 8 Mechanisms of Evolution What is the modern definition of evolution? An example of allele frequency  Population Size = Frequency of Red = , Pink = , White = What is a “gene pool?” How large is this gene pool? _______ genes Frequency of allele A in the gene pool = If hummingbirds prefer to feed at red flowers what will happen to the frequency of the red (A) and white (a) alleles over time? Frequency of A in How modern biologists Population see evolution  Time  9 What causes changes in allele frequencies? 1. 2. 3. 4. Natural Selection A. B. C. D. Examples of Natural Selection in Action I. Beak size in Darwin’s Finches in 1997 there was a drought  Available seeds were less abundant and harder/larger 10  finch population declined  survival was not random: finches with larger beaks had higher survival What happened to the average beak size? Natural Selection can take three forms: The 3 Modes of Natural Selection 11 Natural selection requires two things: a. b. Differential success of genotypes is referred to as ____________________ what is it? what is it not? Genotype A1A1 A1A2 A2A2 Offspring 20 18 5 Relative Fitness What are the two components of fitness? Why is there usually a “trade-off” between the two components of fitness? An important principle: Fitness is not an inherent property of the genotype Explain & give examples 12 Mechanisms of Evolution (cont.) 2. Mutation What is a mutation? What are the 3 possible effects of a mutation? How can mutations be both unimportant as a mechanism of evolution (changing allele frequencies) and at the same time absolutely essential for evolution? Important Principle: mutations are random & don’t occur in response to “need” of species for trait Example: 3. Genetic Drift define: What does it look like  Frequency of A in Population Time  13 examples of things that result in random changes in allele frequencies:   random mortality sexual recombination What is the effect of population size on drift? (illustrate this in the graph above) Can you explain why? There are two special cases of genetic drift that cause random changes in allele frequencies. a. bottleneck effect Population Size Time  b. Founder effect Why are neutral alleles more prone to genetic drift than harmful or beneficial alleles? 14 4. Gene flow also known as ___________________ rate of gene flow depends on … What are the effects of gene flow? Hardy-Weinberg Theorem Think of it as biology’s version of Newton’s First Law (bodies remain at rest unless acted on by external forces) Allele frequencies remain constant when,     Of the 4 mechanisms of evolution mentioned above which one(s) result in adaptive change within a population? Which one(s) result in random change? 15 Adaptation noun – a trait that improves the fitness of an individual or species and verb – the process of natural selection Species may have similar adaptations due to common ancestry or convergent evolution Homologous traits what are they and what do they tell us about how evolution works? not to be confused with Analogous traits How do we tell the difference? Tasm. Wolf Kangaroo Deer Lion Wolf Analogous traits result from _____________________ evolution 16 Convergent evolution shows that adaptation by natural selection is not a random process - same adaptations evolve more than once (independently) example: Demonstration of the vertebrate blind spot (close left eye and stare at letters with right eye. Spot disappears.) 17 Quiz: are these similar because of convergence or shared ancestry? • Wings of birds and bats • Skull of birds and bats explain: T. rex Birds Lizards Kangaroo Bats Ancestral Reptile What is it called when two species evolve, each in response to the other? Examples: 18 LIMITS TO NATURAL SELECTION 1. The environment keeps changing . . . and … What is the Red Queen Hypothesis? Corollaries of the Red Queen Hypothesis a. current adaptations reflect past environments. b. c. If the environment changes faster than a species can adapt it ___________________________ 2. Natural Selection works by modifying pre-existing structures … so_________________________________________________   Why do we have 4 limbs? Vertebrate skeleton illustrates the principle of ________________________________  The Panda's "thumb" Why is evolution more like a tinkerer than an engineer? Can you think of other examples of jury-rigged designs in nature? 19 Because of #2 . . . 3. Adaptation may represent local optimum rather than a global optimum "Adaptive peaks" in an “adaptive landscape” Fitness Trait Important Principle: There may be better solutions, but only intermediate traits that increase fitness will be favored by natural selection. Can you think of other examples? 4. Physical and Biological Constraints 20