Evolution “Nothing in Biology makes sense except in the light of evolution”- Theodosius Dobzhansky
Darwin • Charles Darwin Born 1809, Death 1882 • Naturalist, family man, married to cousin Emma and had 10 children. • Published “On the Origin of the Species” in 1859 after collecting evidence and developing the theory for many decades. • His theory of evolution by natural selection has held true and is supported by an overwhelming body of evidence. • Despite the evidence it has remained a controversial theory and has changed in popularity over the years. • Evolution= change over time in a population in traits.
Variation • The color of human eyes, skin and hair is primarily controlled by the amount and type of a pigment called melanin. Specialized cells known as melanocytes produce the melanin, storing it in intracellular compartments known as melanosomes. The overall number of melanocytes is roughly equivalent for all people, however the level of melanin inside each melanosome and the number of melanosomes inside a melanocyte varies. The total amount of melanin is what determines the range of hair, eye and skin colors.
Differential Reproduction • While evidence is still being collected, most scientists agree that the natural selection for the lighter eye colors are linked to the relaxation of selection for the darker skin tones. As human ancestors began to migrate to various places around the world, the pressure for selection of dark skin color was not as intense. Particularly unnecessary to human ancestors that settled in what are now the Western European nations, selection for dark skin and dark eyes was no longer necessary for survival. These much higher latitudes afforded different seasons and no direct sunlight like near the equator on the continent of Africa. Since the selection pressure was no longer as intense, genes were more likely to mutate.
Heredity • Right now there are three known gene pairs that control eye color. The bey 2 gene on chromosome 15 contains a brown and blue allele. Also on chromosome 15, the bey 1 gene is the central brown gene. On chromosome pair 19 the gey gene contains a green allele and a blue allele. • A green allele is dominant over a blue allele, and a brown allele is dominant over both green and blue alleles. For the bey 2 gene if a person has a brown allele then they will have brown eyes. In the gey gene the green allele is dominant over the blue allele, but it is still recessive next to a brown allele. For example if a person has a brown allele on chromosome 15, but all the other alleles are blue or green, they will have brown eyes. A green eyed person would have a green allele on chromosome 19 and all or some other blue alleles. Blue eyes are produced only with two blue eye genes. All four alleles must be blue to produce a blue eyed person.
Natural Selection- Postulates • 1. variation of the trait within a population • 2. certain variations of the trait confer a fitness advantage to the individual that has them which allows those that have fitness to reproduce. • 3. this trait variety is passed on to offspring
Micro-Evolution • Microevolution is evolution on a small scale — within a single population. • Mechanisms: Mutation, Genetic Drift, Migration, Natural Selection. • http://evolution.berkeley.edu/evolibrary/article/evo_36
Macro-Evolution • Macroevolution generally refers to evolution above the species level. • Mechanism: Microevolution + time! • http://evolution.berkeley.edu/evolibrary/article/evo_47
Evidence • 1.) Fossil Record-the ordered array in which fossils appear within layers of sedimentary rocks. • 2.) Comparative Anatomy-comparison of body structures in different species, which give signs of common descent • 3.) Biogeography-the geographical distribution of species • 4.) Comparative Embryology-the comparison of early stages of development • 5.) Comparative Molecular Biology-comparison of DNA, RNA and Protein sequences in difference species, which gives signs of common descent on the molecular level • 6.) Population Genetics- using allelic frequencies to show evolution among a population of a species.
Fossil Record • Every fossil ever found supports the theory of evolution by natural selection. • http://www.agiweb.org/news/evolution/examplesofevolution.html
Comparative Anatomy • Sexual dimorphism- males and females in a species that look different. • http://www.blackwellpublishing.com/ridley/a-z/sexual_dimorphism.asp • Organisms that are closely related to one another share many anatomical similarities. • All comparative anatomy studies ever done support the theory of evolution. • http://science.jrank.org/pages/348/Anatomy-Comparative.html
Comparative Anatomy con’t • Vestigial Structures- non functional trait from a past ancestor • http://evolution.about.com/od/evidence/tp/Vestigial-Structures-In-Humans.htm • Homologous morphology and function • http://evolution.berkeley.edu/evolibrary/article/0_0_0/lines_05
Comparative Anatomy con’t • convergent evolution-when two different species have adaptations for a common environment, giving them analogous structures (structures that look & function the same way, but have different genetic makeup) • divergent evolution-when you have a common ancestor and different adaptations in different environments leads to new species, but homologous structures (features that often have different functions but are structurally similar because of common ancestry)
Biogeography • the branch of biology that deals with the geographical distribution of plants and animals • Speciation is a result of natural selection and isolation. • http://evolution.berkeley.edu/evolibrary/article/history_16 • http://evolution.berkeley.edu/evosite/evo101/VCCausesSpeciation.shtml
Comparative Embryology Comparative Embryology is the branch of embryology that compares and contrasts embryos of different species. • http://www-tc.pbs.org/wgbh/evolution/library/04/2/pdf/l_042_03.pdf
Comparative Molecular Biology • the greater number of DNA and Proteins sequence similarity between species, the more likely they share a common ancestor, more closely related (sequence homology) • http://deepblue.lib.umich.edu/bitstream/handle/2027.42/37624/1330270504_ftp.pdf?sequence=1
Population Genetics • The Hardy-Weinberg principle states that a sexually reproducing population will have stable allelic frequencies and therefore will not undergo evolution, given the following five conditions: • large population size • no immigration or emigration • random mating • random reproductive success • no mutation • The Hardy-Weinberg principle proves that variability and inheritance alone are not enough to cause evolution; natural selection must drive evolution. A population that meets all of these conditions is said to be in Hardy-Weinberg equilibrium. Few natural populations ever experience Hardy-Weinberg equilibrium, though, since large populations are rarely found in isolation, all populations experience some level of mutation, and natural selection simply cannot be avoided. Therefore evolution is inevitable when any of the conditions arebroken. In every population in nature, one or more of theses conditions have been broken and therefor evolution is inevitable.