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Developing a Theory C-16-1 Evolution is the process by which species may change over time. A theory is a broad explanation that has been scientifically tested and supported. belief = conclusion held with confidence but not substantiated by positive knowledge or proof The origin of life has many theories and ideas and has been pondered for centuries! Some alternative thoughts and theories… Extraterrestrial Origin (Intelligent Design): *life came from outside earth Divine Creation *life came from a divine being(s) or force. Spontaneous Origin * development through natural chemical and physical processes Theory of Evolution: Presented by Charles Darwin in 1859 - has 4 major points: 1.) Variation exists within the genes of every species (result of random mutation) 2.) In a particular environment, some individuals of a species are better suited for survival and so leave more offspring 3.) Over time, change within a species leads to the replacement of old species by new species as the less successful species become extinct. 4.) There is clear evidence from fossils and many other resources that the species now on Earth have evolved (descended) from ancestral forms that are extinct (evolution). Darwin was a naturalist at heart and actually had a degree in Theology! Studied as a naturalist on the H.M.S. Beagle in 1831 where he made his observations and compiled his theory. *Originally believed that divine creation was the explanation *This view did not account for kinds and distribution fossils found *found on his voyage, similarities and differences between animals of the same species Ex: fossilized armadillos looked similar, but not identical to today's armadillos ie: one gave rise to the other Galapagos Islands: found the plants and animals closely resembled those in nearby S. America Ex: Finches - found many species that all looked very similar but had different feeding habits… all looked similar to a finch in S. America * These birds must have migrated there and changed after they arrived - descent with modification Darwin actually bred pigeons to track traits… ~ by choosing which birds to breed, he was using a process called artificial selection - done by humans instead of nature Most scientist of this time thought that species stayed the same throughout time. This did not explain the fossil record though! Other scientists influenced Darwin's ideas: Lamarck - use or disuse causes structures to enlarge or shrink and stated that all such changes were heritable Ex: giraffes stretched their necks to eat leaves = offspring had longer necks Darwin did not buy this idea, but agreed that traits were passed down to offspring. Lyell, Cuvier, and Hutton - studied fossils * Cuvier thought the fossils showed change in species but the change was sudden, not gradual * Lyell and Hutton thought it was a gradual change ~ Lyell published a book on the topic: ~ showed earth's history was long enough for gradual change to happen Applying Darwin's Ideas C-16-2 Natural Selection: ~ The process by which populations change in response to their environment Population: group of individuals that belong to the same species, live in a defined area, and breed with others in the group Darwin looked to Malthus's ideas about population to come up with the idea of natural selection… Malthus said…* even though life has the potential to reproduce to capacity in a short time, it does not due to death from sickness, war, and starvation So… Darwin's idea of natural selection states * Individuals that possess superior physical or behavioral attributes are more likely to survive than those that are not so well endowed. 4 logical steps to explain this… 1.) Overproduction - all species are capable of making more offspring than will survive to maturity 2.) Variation - variation exist within every population - much in the form of inherited traits 3.) Selection - in any environment, a given trait may make individuals more or less likely to survive to reproduce. Those who survive - pass on genes to their offspring 4.) Adaptation - over time, those traits that improve survival and reproduction will become more common In 1859, he published On the Origin of Species by Means of Natural Selection * Gave a huge amount of evidence that evolution had occurred and also provided a reasonable hypothesis for how evolution takes place. Fossils: These are the most direct evidence for macroevolution ~ Fossils are the preserved or mineralized remains or traces of dead organisms Ex: fossils in older rocks are different than fossils in newer rocks remains = bone, teeth, shells traces = footprints, burrows, imprints Scientists are always looking for "intermediate species" or missing links… Some links have been discovered: * fish and reptiles * reptiles and birds * reptiles and mammals Look at Figure 7 pg. 382 this shows the hypothetical descent of whales from 4 legged land animals. Sadly, the fossil record is incomplete! Some species lived where they were not easily fossilized so we have lost the record of them. ~ For an org. to be fossilized, it must be quickly covered by fine sediment before the body decays, is eaten, or is scattered by scavengers. Good places to be fossilized = wet lowlands, slow moving streams, shallow seas, near volcanoes By using carbon dating, paleontologists can tell how old a fossil is - this allows them to put the fossils in order and come up with a family tree and show common ancestors. Ex: Common ancestor = species from which 2 or more species diverged We can also use genetics to note links between species: ~ We can trace the genetic mutations back to see how far removed one org. is from another! Ex: our hemoglobin has a 146 AA chain … *a gorilla has a hemoglobin 146 AA chain with only one different AA from us!! This shows that we share a common ancestor that was very recent! If there are many differences, then the common ancestor is in the distant past. Now, we can chart the genetic code and show side by side where the differences are in the nucleotides! We use this to make family trees. Anatomy and Development: Looking at the skeletal structure of vertebrates, we can see common ties… Ex: These are homologous structures = they share a common ancestry! Organisms that have bones or other structures that are reduced in size or are modified are said to be vestigial structures Ex: our coccyx (tailbone) does not have the same use as a fish's tail Beyond Darwinian Theory C-16-3 1.) Microevolution occurs as a result of genetic mutation within species over a long period of time. 2.) Isolation will lead to species formation = speciation ~ this is the link bet. macro. and microevolution! isolation = two populations of the same species are separated by a landform or other obstacle species = when individuals of two populations can no longer interbreed Ex: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Speciation Four steps lead to speciation. First, a single species is an interbreeding reproductive community. Second, a barrier develops, dividing the species. Third, separated into different habitats, the divided populations become differentiated through the accumulation of differences. Fourth, so different have the separate populations become, that is when the barrier disappears and they overlap again. Interbreeding does not occur. 3.) Extinction leads to species replacement When a species dies out completely, those that are left continue to live Ex: Reptiles once ruled the earth - due to climactic changes, they were replaced more dominantly by mammals This is called macroevolution! So how do these things happen? Microevolution: These are factors that will affect what kind of genes are in a pop. from one gen. to the next: * Natural selection - can cause increase or decrease in certain alleles in a population * Migration - moving individuals in, out, or between pop's - can change numbers in types of alleles in a pop. * Mate choice - randomly paired parents = random assortments of traits - selective or limited choices = limited set of traits passed on * Mutation - change # and types of alleles from one generation to the next - these are rare * Genetic drift - random effects of everyday life cause differences in the survival and reproduction of certain individuals - therefore, some alleles may become more/ less common Macroevolution * Convergent evolution - species living in similar environments should evolve similar adaptations * Coevolution - species who live closely together will have adapted to one another's existence Ex: the orchid moth - only this type of moth feeds on this orchid and they depend on one another for their existence * Adaptive radiation - over time, species may split into 2 or more lines of descendants (lineages). Many splits yields many different species. * Extinction - all members of a lineage die out * Gradualism - slow, gradual change of differences build up over time to equal large change * Punctuated equilibrium - due to environmental change, some species will change rapidly or "suddenly" appear. If the climate changed drastically, those species that could adapt quickly would be more likely to survive! This provides backing for punctuated equilibrium! Ex: volcanic eruptions, ice ages, asteroid impacts etc. Many species that cannot adapt will succumb to these disasters! ~ This will leave room for species replacement and evolution. Both of these ideas have their followers, but most support gradualism.