Chapter 6: Change Over Time Charles Darwin – The Origin of Species

Key Vocabulary & Concepts Darwin’s Theory Key Vocabulary & Concepts A trait is a characteristic that an organism passes to offspring through its genes. Sexual reproduction results in offspring that are genetically different from each parent. DNA is genetic material that carries information about an organism and is passed from parent to offspring. A (scientific)theory is a well-tested concept that explains a wide range of observations. An adaptation is a trait that helps an individual survive and reproduce. A species is a group of similar organisms that can mate with each other and produce fertile offspring.

What was Darwin’s hypothesis? What is natural selection? A fossil is the preserved remains (solidified/imprints) or traces of an organism that lived in the past. The process of change over time is called evolution. In artificial selection, only the organisms with a desired characteristic, such as color, are bred. (Human controlled) What was Darwin’s hypothesis? **Natural selection is the process by which individuals that are better adapted to their environment are more likely to survive and reproduce more than other members of the same species. Factors that affect the process of natural selection: overproduction, variation, & competition Any difference between individuals of the same species is called a variation. What is natural selection? **Darwin proposed that over a long time, natural selection can lead to change. Helpful variations may accumulate in a species, while unfavorable ones may disappear.

What evidence supports evolution? Evidence of Evolution What evidence supports evolution? **Fossils, patterns of early development, similar body structures, and similarities in DNA and protein structures all provide evidence that organisms have changed over time. FOSSILS The Earth’s crust is arranged in layers of different types of rock. Older layers are deposited before newer layers and are therefore deeper in the crust. Fossils are found in the rock layers. They provide a historical sequence of life called the fossil record(ex. Fossils found in the upper layers tend to resemble present day organisms, deeper layer fossils tend to look quite different) Gaps remain in the fossil record because: fossils only form under certain conditions (must be free of oxygen) not all organisms form fossils scientist haven’t excavated all the rock on Earth

PATTERNS OF EARLY DEVELOPMENT SIMILAR BODY STRUCTURES Embryonic Structure: early embryos are nearly indistinguishable among major groups such as vertebrates SIMILAR BODY STRUCTURES Homologous Structures : bones in differing species are often found in the same amount and position. These bones have been modified over time for different purposes. Organisms that have similar body structures share a common ancestor. Vestigial Structures: Remnants of once useful structures that no longer have a purpose (ex. Whales have hind-limb bones in their bodies)

SIMILARITIES IN DNA & PROTEIN STRUCTURES Genes are segments of DNA. New genetic studies allow for DNA comparison. The more similar the DNA sequences, the more closely related the species are. If organisms have evolved from a common ancestor, they must share much of their genetic information which has shown to be the case. In most cases, evidence from DNA and protein structure has confirmed conclusions based on fossils, embryos, and body structure. Section of Cytochrome c Protein in Animals The table shows the sequence of amino acids in one region of a protein, cytochrome c, for five different animals. Each letter corresponds to a different amino acid in the protein. http://www.youtube.com/watch?v=GZCL3gv9kEM

What patterns describe the rate of evolution? Rate of Change How do new species form? Natural selection explains how variations can lead to changes in a species, but how could an entirely new species form? A new species can form when a group of individuals remains isolated from the rest of its species long enough to evolve different traits that prevent reproduction. What patterns describe the rate of evolution? Scientists have developed two patterns to describe the pace of evolution. Gradualism: small changes that add up to major changes over a long period of time (slowly and steadily) Punctuated Equilibrium: species evolve during short periods of rapid change (quickly over short periods of time)