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Evolution Evolution- the theory that species change over time Charles Darwin- 1859 published On The Origin of Species Darwin’s Theory of Natural Selection Overproduction- in nature there is a tendency for organisms to produce more offspring than can survive Most of the young do not survive to reproduce. Variation All populations contain heritable variations - size, speed, agility, coloration Some variations are more favorable Natural Selection Those with favorable variations are more likely to survive and pass on their favorable variations Natural Selection and Adaptations Natural Selection can be applied to explain the evolution of adaptations in organisms Mimicry - copies the appearance of another species Camouflage - blends in Evidence For Evolution Fossils can show evolutionary changes over time but can give an incomplete picture What fossil evidence is missing? If all animal species evolved from common ancestors, there should be fossils of the intermediate species found. The only “intermediate” fossils found have been of the birds. Examples: Archaeopteryx & Microraptor gui This fossil was discovered in late 2002 in China. It appears to be a 4-winged bird and a possible link between the reptiles and birds. Biological Evidence for Evolution All living things are made of the same chemical elements- C, N, H, & O Chromosomes are all made of DNA Proteins are synthesized in essentially the same way Biochemical, Embryological, Anatomical similarities Biochemical Evidence Comparison of nucleotide sequences in the DNA of species Embryological Development Some organisms are similar to one another until late in embryonic development One theory hypothesizes that during its embryological development, an organism retraces its entire evolutionary history. For example, humans begin life as a single cell, then grow into a multicellular organism in water. Early in fetal development, humans, like other vertebrates have what appear to be “gill slits” on the side of the neck area. "The throat (or pharyngeal) grooves and pouches, falsely called "gill slits" are not mistakes in human development. Far from being useless evolutionary vestiges, then, these so-called "gill slits" are quite essential for distinctively human development." Homologous Structures Similar arrangement in structure, vary in function, but are derived from the same structures in the embryo Analogous Structures Serve the same function but differ in structure represents convergence - a similar solution to an adaptive problem Vestigial Structures Nonfunctional or partially functioning remnants of organs that were functional in their ancestors Patterns of Evolution Divergent Evolution - two or more related species become more dissimilar. Involves an adaptive radiation when species of related ancestry exploit different aspects of the environment Convergent Evolution - Unrelated species become more and more similar as they adapt to the same kind of environment What Causes Variations in Traits? Gene Pool - collection of genes for all the traits in a population Allele Frequency - percentage of a specific allele of a gene in the gene pool A population in which allele frequencies do not change is in “genetic equilibrium.” Genetic Equilibrium - A state of evolutionary stability. No mutations occur Individuals neither enter or leave the population through migration The population is large and remains relatively stable. Individuals mate randomly & natural selection does not occur. Disruption of Genetic Equilibrium Mutation - physical change in a gene or chromosome, will produce new alleles for a trait Migration - movement of individuals into or out of a population Genetic Drift Allele frequencies in a population change as a result of random events or chance, occurs in small to medium-sized populations Formation of Species Natural selection causes the most significant genetic changes in a population. These changes do not necessarily lead to speciation- formation of a new species. Isolated Populations Geographic Isolation - physical separation of members of a population Reproductive Isolation - inability of formerly interbreeding organisms to produce offspring Gradualism Species originate through a gradual buildup of new adaptations Punctuated Equilibrium Speciation occurs in rapid bursts with long periods of stability in between Extinction Species die off Many extinctions are due to human destruction of habitats