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Evolution The Unifying Theory of Biology
Contemporary Scientific History of the Universe billion years in 30 volumes - each volume = 450 pages -each page = 1 million years Big Bang, p. 1 Origin of Earth Life BeginsComplex Animal Life Dinosaurs pp Modern Humans p. 450, last sentence
What is Evolution?
Evolution = Descent with Modification Species originate as modified descendants of other species. Biological evolution is the origin of new species from previously existing ones over time.
“As many more individuals of each species are born than can possibly survive, and as consequently there is a frequently recurring struggle for existence, it follows that any being, if it vary in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of survival and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.” Charles Darwin, The Origin of Species
Darwin’s Theory If there is a struggle for existence… If heritable variations exist among members of a population… If these variations affect survival and/or reproduction… Then species will change over time.
There is a struggle for existence. Species tend to produce more offspring than the environment can support. Darwin calculated that even one slow-breeding female elephant could give rise to 19,000,000 elephants after 750 years if all of her young survived and reproduced at the same rate. Obviously, the environment cannot support all elephants that are born.
Heritable variations exist. An impressive amount of variation exists within living species. Breeders of animals and plants use these diverse characteristics to establish new varieties of dogs, cats, pigeons, wheat, cotton, corn, and other domesticated organisms.
Variations affect survival & reproduction. Certain individuals possess inherited traits that make them more likely than other individuals to survive and/or reproduce. “Differential survival and reproduction”
Species will change over time. Evolution in Action
Populations evolve, not individuals. Individuals may change throughout their lifetimes, but this is not evolution. Evolution occurs across many generations. Over time, populations acquire new characteristics that enhance their ability to survive and/or reproduce in a given environment.
Variations are “Random” Mutation and sexual recombination occur randomly. The variations that occur do not anticipate the “needs” of the organism. In this sense, “random” does not mean that anything can happen.
Natural Selection is NOT Random Genetic variation occurs randomly, but natural selection is NOT random. Genetic variations that aid survival and reproduction are more likely to become common than variations that do not. Nature imposes a direction to evolutionary development. Though dolphins are more closely related to humans than they are to sharks, they have evolved bodies adapted to an aquatic environment.
Evolution is About Consequences Evolution is historically contingent, that is, “windows of opportunity” constantly open and close. Once certain changes have occurred, the range of possible future changes is permanently altered.
“Windows of Opportunity” The earliest turtles could not retract their necks. Proganochelys 220 million years ago Proganochelys 220 million years ago side neck turtles (southern hemisphere) side neck turtles (southern hemisphere) vertical neck turtles (northern hemisphere) vertical neck turtles (northern hemisphere) Later, two distinct forms of neck retraction evolved. With the extinction of the turtles that could not retract their necks, the possibility that another form of neck retraction would evolve was lost.
Evolution is Predictive Tiktaalik roseae Ichthyostega Eusthenopteron Panderichthys Acanthostega Tiktaalik 385 million years ago 365 million years ago ? ?
Evolution is Testable Human & Ape Chromosome Numbers Hypothesis: Human chromosome 2 resulted from the fusion of two chromosomes present in the common ancestor of humans and the other great apes Human chromosome number is Chimpanzee chromosome number is Gorilla and orangutan chromosome numbers are Detailed analysis confirms that four species share ancestry Banding patterns of humans and chimpanzees match Telomeres in the middle of human chromosome 2. centromere telomeres
Evolution is Testable Human & Ape Chromosome Numbers 1958 Human chromosome number is Chimpanzee chromosome number is Gorilla and orangutan chromosome numbers are Detailed analysis confirms that four species share ancestry Banding patterns of humans and chimpanzees match Telomeres in the middle of human chromosome Sub-telomeric sequence confirmed by DNA analysis Precise fusion point sequenced Chimpanzee genome sequenced. centromere telomeres 1992 Second centromere discovered.
Evolution is Testable Human & Ape Chromosome Numbers These scientists were not limited to simply noting the similarities in the chromosomes. They were able to use evolutionary theory to consistently predict what they would later confirm to be correct. Video
Is Evolution a Theory or a Fact? Evolution is both a fact and a theory. Scientists no longer really question the basic fact that evolution has occurred. The concept of common descent has withstood nearly 150 years of extensive testing. There are various competing theories used to explain HOW evolution happens.
Is Evolution Controversial? The socio-political controversy stems from the notion science is trying to explain phenomena that some religions have already explained. The genuine scientific disagreements concern technical points about how evolution happens, not whether it has occurred.
Conclusion “Nothing in Biology makes sense except in the light of evolution.” Theodosius Dobzhansky ( )