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Lecture 8

8. Lecture Eight - October 4.docx

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Jessica Hawthorn

PRECAMBRIAN LIFE The eye is often cited by those that do not accept evolutionary theory as an example of something that is too complex to have evolved. How can you have an intermediate stage in the evolution of the eye, they ask? The diagram shows that the eye has in fact evolved from an organ in its primitive stages to an advanced organism with complex functions. Evidence for Evolution Evolution of horses - Increasing specializations for fast locomotion - Increasing body size - Specializations for chewing The hoof on a horse is a single digit. It has one finger and one toe. They‟ve lost all the other fingers. Over time, they‟ve lost their fingers from five digits to just two digits. Now, only the middle finger and the thumb are left on a horse‟s hoof. Horses start with having molars similar to ours. Over time, horses get bigger, reduce the number of digits on their fingers, and their teeth become more specialized for chewing. All of this happens because the environment that they inhabit changes. They develop specialized adaptations for living in open environments. In the time period that we‟re speaking of, you have North America going from being a tropical jungle to open plains. Horses adapt by getting larger, reducing digits no their fingers, and becoming specialized. However, they don‟t do it just one way. Many different species of horses evolve. What are whales? People thought they were fish for the first couple thousand years. We realized that whales are mammals. Starting about 25 years ago, concentrated research discovered fossil records that show that whales are related to COWS. Eventually, whales became adapted for aquatic environments? Why did they adapt? Fish! Whales are carnivores, and can easily access food (i.e., fish) in the oceans. In an aquatic environment, you have a rich food source. We see progressive evolution of adaptations. By about 23 million years ago, we have the modern whale groups that we know of today. To remove any doubts, the genetic data also shows the same thing as the fossil record about whale evolution from cow-like animals. Fossil, genes, Darwin, Mendel, and all of the data that Darwin collected have all been combined into the modern theory of evolution. This is known as the Neo-Darwinian Synthesis: Combination of genetic, organismal biology, and historical geology in study of evolution The Neo-Darwinian Synthesis proposes the following: 1. Variation is product of genetic mutation/change and recombination. 2. Evolution occurs as changes in frequency of alleles between generations. As taller giraffes reproduce and survive more than smaller giraffes, the next generation will have greater numbers of taller giraffes and decreasing numbers of shorter giraffes. In the next generation, an even greater percentage of the giraffe population will be composed of taller giraffe. 3. Speciation occurs through reproductive isolation (which is often the result of geographic isolation. How fast does evolution work? You could possibly create one species from another species within 15-20 generations. For us humans, it would take very long for a new species to emerge from the human species. Evolution is not a continuous process. Darwin had a sense that evolution was occurring over a long period of time. Darwin had a sense that evolution took a long time, but he wasn‟t sure if it was constant. Punctuated Equilibrium: evolution occurs in geologically rapid bursts that punctuate periods of little change (stasis). Evolution is a start-stop process. So, you can have a species just reproducing and passing on its genes in a regular environment. However, if there is environmental change, natural selective forces will act to assist some members of the species, which will survive and pass on their acquired traits to their offspring. Extinction: Background Extinction: independent extinction of individual species through evolutionary processes (e.g., evolution of a daughter species). One form of background extinction is when you have a parent population which evolves into two daughter populations. Another form of it is when, for example, you have a new species that can evolve in one lake in the middle of the desert. This species will probably go extinct when the lake goes away. Mass extinction: extinction of multiple species due to common cause. A common cause wipes out multiple species in different environments. Mass extinctions affect species. Ultimately, extinction is always caused by some form of environmental and climate change. Possible causes of mass extinction (climate change) Earth is a dynamic planet. Conditions, weather, climate, ocean levels, and the surface of the Earth are changing all the time. Changes that occur in the Earth: - Continental configuration - Ocean circulation patterns - Sea level change - See Prof’s notes Most of the large scale extinction events have generally involved some fairly rapid change to the environment. The dinosaur extinction event may or may not have to do with a meteorite impact. This is a model that has not been proven with certainty. When you have a mass extinction, you have new geographical areas which open up for new species to come in and take over. When the dinosaurs disappear, grasslands open up, forests open up. Habitats which were occupied by large-bodied reptiles are now filled with large-bodied mammals. The number of species on Earth has increased over time b
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