Theory of evolution

Many ideas were out there to explain how species change over time but the first published was Charles Darwin in the H.M.S. Beagle traveled the world for 5 years and made observations of living and fossilized plants and animals. Started to notice relationships among species Most significant stop- the Galapagos Found many unique species similar but different then those of the mainland. IDEA CAN SPECIES CHANGE OVER TIME?

Now that an idea was formed DARWIN had to collect evidence For two decades Darwin worked and experimented and read and borrowed from Thomas Malthus. Malthus idea was that human population grows faster than food supply Darwin idea was that individuals struggle to compete in changing environmental conditions. Which individuals survive?

Natural selection Mechanism for change in populations. In Nature organisms produce more offspring than can survive Due to independent assortment in any population individuals have variations Individual with useful variations will survive Over time offspring with certain variations make up most of the population and may look nothing like their ancestors In Indonesia Alfred Russell Wallace reached a similar conclusion but Darwin was the first to publish.

Interpreting evidence after Darwin Much data has been gathered but as Humans have only been here a short time and what happened before us is subject to interpretation.

Evidence for Evolution Adaptation is variation that aids an organism’s chance of survival in its environment. Structural adaptations Mimicry Camouflage Physiological adaptations Fossils Anatomy Homologous structure - Analogous structure Vestigial structure Embryology- viruses Biochemistry- Modern approach

Mechanisms of Evolution What was missing from Darwins theory? Genes Who evolves Populations or individuals? Natural selection acts on the range of phenotypes Evolution occurs as a population genes and their frequencies change over time Gene pool How much (percentage) of any specific allele in the gene pool is called Allelic frequency

Genetic equilibrium When the frequency of alleles remains the same over generations Does it evolve?

Changes in genetic equilibrium Mutation -most lethal but some……. Are useful Genetic drift- change of allelic frequencies by chance events… can greatly affect small populations making recessive alleles more common than in the larger population, Gene Flow- Can be affected by movement into and out of a population                                                                                                                                                                                                                                              GO TO PAGE TWO

Three types of natural selection that act on variation Stabilizing-favors average individual in a population

Directional selection Occurs when Natural selection favors on of the extreme variations of the trait

Disruptive selection Individual with either extreme of a trait’s variation are selected for.

Physical barriers can prevent interbreeding rendering a new species (speciation) can no longer interbreed Geographic isolation- When a physical barrier divides a population Reproductive isolation Change in chromosome numbers and speciation Speciation rates Gradualism- slow change over time Punctuated equilibrium- rapid change

Patterns of evolution Adaptative radiation

Divergent evolution- become more dissimilar over time

Convergent evolution Unrelated species occupy similar environments which have similar pressures which make them look similar

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