UNIT 5 PART 1: EVIDENCE OF EVOLUTION Evolution is a gradual change over time. There are two kinds: Geological – a change in the earth over time Organic – a change in species over time

Evidence from the Past - Fossils A fossil is any trace or remains of an organism that has been preserved by a natural process. Scientists can compare these to living organisms to see if evolution has occurred. Special circumstances are needed for fossils to form and then usually only the hard parts are left.

Relative Dating of Fossils Most fossils are in sedimentary rock which forms layers. If the layers are undisturbed the oldest is on the bottom and the youngest on top. Therefore, the oldest fossils are found in the bottom layer. This tells you which fossils are older. Determining the order of the fossils results in the fossil record.

Earliest organisms were simple, later ones more complex. Unicellular organisms appeared before multicellular. Aquatic organisms appeared before land animals. Patterns of Evolution

There are sequences in the fossil record that indicate that later species developed from earlier ones through a series of gradual changes passed on from generation to generation. These occurred over millions of years in the species. The fossil record is considered the strongest evidence of evolution.

Evidence from Living Organisms The classification system that we use is based on similarities and differences in anatomy, embryological development, and biochemistry. Similarities indicate a common ancestor. The more similarities between organisms the more closely related they are.

Comparative anatomy Vestigial structures – parts that are reduced in size and have little or no function. Human appendix, tail bone, wisdom teeth and muscles that move the ears and nose Whale hip and leg bones

Homologous Structures Parts that have similar structures and development (are built the same way) but have different functions: Human arm Cat leg Whale flipper Bat wing Indicates a common ancestor

Analogous Structures Parts that have the same function but a different structure and development (they are made differently): Bird wing Insect wing Indicates evolution along different lines

Embryology The embryos of closely related species show similar patterns of development. As development continues the embryo resembles the adult. The longer the embryos resemble each other, the closer related they are.

Comparative biochemistry The ability to read the amino acid sequence of proteins and the DNA of an organism letter by letter has enabled biologists to confirm evolutionary relationships. The more closely related organisms are, the greater the biochemical similarities will be in the sequences of DNA, proteins, and enzymes.

Geographical distribution Using geography to determine what species evolved where. If a species is found in only one location (must have evolved there). Ex. Australia has between 600,000 and 700,000 species of plants and animals. Approximately 3/4 of living plant and mammal species are species found only there.

Direct Observation Evidence from observed natural selection. Examples for the evidence for evolution often stems from direct observation of natural selection in the field and the laboratory Ex. Darwin’s studies on Galapagos Islands; the Grants’ studies on finch beaks

Recall the mechanisms of evolution Natural Selection organisms having traits that better enable them to adapt to specific environmental pressures will tend to survive and reproduce in greater numbers than others of their kind (survival of the fittest) Genetic Drift describes random fluctuations in the number of variations of a gene in a population. Alleles increase and decrease by chance over time

And how they account for the diversity of life Natural selection   Predators, changes in climate, competition for food forces organisms to change in order to survive. These forced changes allow for diversity among organisms. Genetic Drift Variety of alleles may decrease or increase by chance Can lead to speciation (increase biodiversity)