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Evidence of Evolution. Homology and Analogy. A homologous feature is a structure with a common evolutionary origin that may serve different functions in modern species (e.g. a bat wing and a human arm)
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Homology and Analogy • A homologous feature is a structure with a common evolutionary origin that may serve different functions in modern species (e.g. a bat wing and a human arm) • An analogous feature is a structure that performs the same function as another but is not similar in origin or anatomical structure (e.g. a bird wing and an insect wing)
Homology • As the theory of evolution suggests, we should expect to find relationships between structures of organisms that come from a common ancestor • This evidence can be seen in structures with very different functions such as the bones within a horses leg and a whales flipper. • The structure were modified slightly as each species evolved, but still maintained similar structural positions
Analogous features • Organisms with no close common ancestor have evolved to have structures with similar purposes but very different structures • Structures have evolved independently of each other
Vestigial structures • Rudimentary and non-functioning/ marginally functioning structure that is homologous to a structure in closely related species • These structures, useful in closely related organisms have become useless or greatly distorted as the organism evolved • Examples: fish that have eye-sockets but no eyes, a running animal that has toes that never touch the ground, organs that serve no apparent function (appendix), hip bones in whales etc..
Some large snakes and whales have vestigial hip bones, that do not support walking, but are homologous to hip bones that support hind limbs of other vertebrates Human Examples: The appendix: May have once served as a mechanism of leaves in primates The tail bone: Served as a support structure for an ancestral tail Male nipples: formed in an early evolutional stage of the fetus, when the sex of the future baby is not yet established Wisdom teeth: presently not used in chewing, but functional in primates who possessed larger mouths. Goosebumps: circular muscles contract to make hair stand up. In animals with fur this would increase insulation
Biogeography • The scientific study of the geographic distribution of organisms based on both living species and fossils • A pattern of distribution of organisms can be explained by plate tectonics and evolution: • At one time all continents were a single mass. It is to be assumed that due to migration species would disperse across the continent. • If no evolution was taking place then similar organisms should be of the same species in similar ecological niches • This is not the case, we can see organisms across the globe that show similar characteristics but are considered different species
After species distributed, organisms evolved and diversified. Species separated by moving continents evolved so much that some even evolved into new species • Ex. Marsupials are not seen to be evenly distributed around the globe. Kangaroos are not found in North America, but the Virginia opossum is. Both Marsupials, but very different species. http://www.youtube.com/watch?v=agWifxus0Ls
Modern Findings…. • Radiometric dating • Pseudogenes • Homologous genes
Radiometric dating • A technique for determining the age of an organism using radioactive decay • Based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates. • Used even to determine the age of the Earth, fossils and remains
As soon as a living organism dies, it stops taking in new carbon. The ratio of carbon-12 to carbon-14 at the moment of death is the same as every other living thing, but the carbon-14 decays and is not replaced. The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample. • Has helped us definitively determine the age of fossils and rocks. Helped develop a timeline of evolution
Homologous genes and Pseudogenes… • All base pair combinations code for the same proteins regardless of the species • Genes inherited from a common ancestor have evolved because of mutation over time, to create variability • The more closely related 2 species are the more similar their homologous genes are
Pseudogenes… • Genes that have undergone mutation and no longer serve a useful purpose • Ex. Dolphins are thought to have evolved from land mammals. Land mammals have approximately 1000 functioning olfactory receptor (OR) genes and dolphins have all these genes, but only 200 are functioning • Humans have a mutated gene for vitamin C production, where most closely related species can produce their own vitamin C • The stomach of the platypus has 3 mutated genes for producing chemicals for digestion even though they completely lack chemical digestion
