18.1 Understanding Evolution (M1)

• Evolution by natural selection describes how species change over time
• James Hutton proposed that geological change occured gradually by accumulating small changes over long periods of time. This idea contrasted with the popular view, which was that the planet's geology was a result of catastrophic events occuring during a brief past.
• Charles Lyell popularized Hutton's views, believing that the Earth was billions of years old, which gave more time for gradual change in species.
• Jean-Baptise Lamarck published a book detailing a mechanism for evolutionary change. This mechanism is now referred to as an inheritance of acquired characteristics by which the environment causes modifications in an individual, or offspring could use or disuse of a structure during its lifetime, and thus bring about change in a species.
• Darwin observed species of organisms on different islands that were clearly similar, yet had distinct differences. For example, the ground finches on the Galapagos Islands comprised several species with a unique beak shape, which closely resembled another finch species on the South American mainland. He imagined that they might be species modified from one of the original mainland species. He later realized that each finch's varied beaks help the birds acquire a particular type of food.
• Natural Selection, or "survival of the fittest", is the idea that there is more prolific reproduction of individuals with favorable traits that survive environmental change because of those traits. This leads to evolutionary change.
• Darwin argued that natural selection was an inevitable outcome of three principles of nature. 1- Most characters of organisms are inherited (passed from parent to offspring). 2- More offspring are produced than are able to survive, so resources for survival and reproduction are limited. Thus, there is competition for resources in each generation. (1/2)
• Darwin argued that natural selection was an inevitable outcome of three principles of nature. 3- Offspring vary among each other in regard to their characterisics and those variations are inherited. Offspring with inherited characteristics which allow them to best compete for resources will survive and have more offspring than those with variations that are less able to compete. Because characteristics are inherited, these traits will be better represented in the next generation. This will lead to change in populations over generations in a process called descent with modification. (2/2)
• Ultimately, natural selection leads to grater adaptation of the population to its local environment. It is the only mechanism known for adaptive evolution.
• Natural selection can only take place if there is variation, or differences, among individuals in a population. These differences must have some genetic basis, otherwise, the selection will not lead to a change in the next generation.
• Genetic diversity comes from two main mechanisms- mutation and sexual reproduction. Mutation, a change in DNA, is the source of new alleles, or new genetic variation in any population. The genetic changes caused by a mutation can have one of three outcomes on the phenotype. Can produce lower fitness (lower likelihood of survival/fewer offspring), higher fitness, no effect on fitness (neutral mutations). (1/2)
• Genetic diversity comes from two main mechanisms- mutation and sexual reproduction. When two parents reproduce, unique combinations of alleles assemble to produce the unique genotypes and phenotypes in offspring. (2/2)
• An adaptation is a heritable trait that helps an organism's survival and reproduction in its present environment. Groups of organisms adapt to their environment when a genetic variation occurs over time that increases/maintains the population's "fit" to its environment.
• Divergent evolution describes when two species that evolve in diverse directions from a common point. Ex: reproductive organs of flowers share same anatomy, but can look very different due to different environments and adaptations to different pollinators.
• Convergent evolution decribes when similar traits evolve independently in species that do not share common ancestry. Ex: both bats and insects can fly, but their wings have evolved from different original structures.
• Evidence of Evolution: 1- Fossil records show similar morphology and progressions of evolution. 2- Anatomy and Embryology- the presence of structures in organisms that share the same basic form. 3- Environment can lead to convergence of form in organisms (ex: can be unrelated but develop similar traits). Embryology (developmental study) can show relatedness between divergent organisms (sturctures that are absent in groups often appear in embryonic forms). (1/2)
• Evidence of Evolution: 4-Biogeography (geographic distribution of organisms) follow patterns can be explained by evolution and tectonic plate movement over time. 5- Molecular Biology (molecular structures of life like DNA) can reflect descent with modification. DNA's universality reflects evidence of a common ancestor for all of life. (2/2)
• Vestigial Structures are structures that are no longer used but are still present in the body. These appear to be residual parts from a past common ancestor.
• Analogous structures are structures that have similar functions due to environmental constraints but are not identical, as they are not a product of close evolutionary relationship.
• Homologous structures are similar physical features in organisms that share a common ancestor, but the features serve completely different functions. An example of homologous structures are the limbs of humans, cats, whales, and bats.
• Misconceptions of Evolution- 1- Evolution is just a theory. A theory in science in a body of thoroughly tested and verified explanations for a series of observations. 2- Individuals evolve. Evolution is the change in a population's genetic composition over time. 3- Evolution explains the origin of life. Evoluion just explains how populations change over time and how life diversifies the origin of species. (1/2)
• Misconceptions of Evolution- 4- Organisms evolve on purpose. 5- Genetic variation is caused by environmental changes. The variation that natural selection works on is already in a population, it doesn't arise in response to environmental changes. (2/2)
• Evolution is not goal directed, and species don't get better over time. They simply track the changing environment with adaptations that maximize reproduction in a particular environment at a particular time.