1) Natural Selection Meiosis (sexual reproduction) and mutations gives us genetic variation. MUTATION: a change in a gene If the population’s gene pool changes, then the species evolves. Two Types of Mutations: (1) Changes in genes in somatic (body) cells: can affect the organism itself, but cannot be passed to sexually produced offspring. (2) Changes in genes in gametes (egg and sperm): do not affect the parent organism itself, can be passed to sexually produced offspring Mutations may result in a trait that improves an organism’s chances for survival, so that organism would be more likely to reproduce. Then the favorable mutation would be passed on to offspring. This results in evolution. Mutations occur very rarely (and are almost always bad), so populations evolve slowly. NOTE: EVEN THOUGH EVOLUTION GENERALLY OCCURS SLOWLY…IT SOMETIMES CAN OCCUR RAPIDLY 1) Directional Selection Selection AGAINST one extreme phenotype (physical type) This causes one extreme phenotype to become much more common (the population is pushed in 1 DIRECTION) Ex. Peppered Moths 2) Disruptive Selection Selection AGAINST the normal phenotype (physical type) This causes BOTH extreme phenotypes to become much more common (the look of the population is DISRUPTED) Ex. Dog breeding 3) Stabilizing Selection Selection AGAINST the extreme phenotypes (physical type) This causes the NORMAL phenotype to become much more common (the look of the population is STABILIZED) Ex. Human weight at birth 2) Genetic Drift – changes in gene pool due to chance (has greater effect on smaller populations) Examples ◦ 1) Bottleneck effect – drastic decrease in population size may leave only certain alleles available. These alleles will quickly be perpetuated. ◦ 2) Founder effect –When a few individuals colonize a new area (same reasoning as bottleneck) 3) Gene flow Introduction or exit of alleles in a population whenever individuals enter or leave. 1) Molecular Biology All living things use DNA and RNA. The genetic code amongst all living things is universally the same. (In other words, the fact that the RNA codon AUG gives the amino acid MET in humans is seen in every other living thing as well) This fact more than any other (at least to me) indicates that all living things originated from a common ancestor. Molecular Biology – Continued The closer 2 different species DNA is to one another, then the closer those 2 are related. Which 2 species are closer related? Species A: AACTGGCTTA Species B: AACTAACCCG Species C: TACTGGCTTA The remains or traces of organisms that have once lived on Earth. Fossil Record: the history of life on Earth, based on fossils that have been discovered The fossil record shows how organisms have changed over time and shows that the Earth is about 3.5 billion years old. Extinctions occur when there are major changes in the environment and species do not have the adaptations to survive. The fossil record helps scientists to discover relationships between different groups of organisms and determine common ancestors. The Earth is divided into layers called strata. Generally speaking, the lower the strata = the older the layer of Earth (each new layer becomes stacked on the older layer below it) This means if two fossils are found, the fossil found in the lowest layer would be the oldest There are also techniques for determining the absolute (or relatively exact date) of a fossil’s age Convergent evolution – process by which different species evolve similar traits (SAME FUNCTION, DIFFERENT ANCESTOR) Example: Birds, bats, and moths have wings, but they did not evolve from a recent common ancestor. Caused by: ◦ living in similar habits / performing similar functions Structures with closely related function but do not come from the same ancestral structure ◦ Same function, different structure Example: Birds, bats, and moths have wings, but they did not evolve from each other. Divergent evolution- build up of differences between groups which can lead to the development of a new species In other words, two different species that evolved from the same ancestor. Caused by populations of the same species: 1. moving to two different environments or.. 2. specializing in different areas of the same environment Structures in different species that originated from common ancestor May have different function but similar structure Evidence for Evolution – Comparative Anatomy Vestigial structures – no longer have a use, but may have had a use in evolutionary history. Ex: human tail bone (coccyx) made of 4 fused vertebrae that resemble the bones in an animal’s tail. Other examples: the appendix, and ear muscles! When two or more species have evolved together, the situation is called coevolution. Example: ◦ Insects and Flowers Flowers provide food for insects. Insects take pollen from one flower to the next so they can reproduce.