Ch.10: Principles of Evolution

People Who Influenced Darwin

Before Darwin Most people believed that the Earth was only a few thousand years old, and that it was unchanging Around the 1700s, these ideas began to change

Hutton & Lyell Believed that geologic features of Earth must have taken a long time to form, therefore Earth must be much older than a few thousand years Also believed that Earth is and has always been changing Darwin figured that since the Earth is changing maybe living things change as well

Lamarck 1st to come up with a hypothesis about how organisms evolve Believed that body structures would become larger or smaller due to use or disuse during an organism’s lifetime, & that those acquired traits could be passed to offspring His hypothesis was wrong, but he was correct in that organisms do adapt to their environments

Malthus Malthus was an economist who said that the human population was growing faster than the food supply, so eventually resources would run out Darwin believed that this applied even more strongly to plant and animal populations, since they reproduce so much faster than humans

Section 2: Darwin’s Observations

Variation Variation is the difference in the physical traits of an individual from those of others Examples: Tortoises who live on islands where vegetation is high have high shell edges and long necks to reach food & those who live on islands with low vegetation have short necks & legs Finches have beaks that matched the food that they eat

Adaptation An adaptation is a feature that allows an organism to better survive in its environment Adaptations can lead to genetic change in a population over time

Darwin’s Evidence Fossils Darwin found looked similar to living species, suggesting that they could be the ancestors of modern species Darwin also found fossils of marine organisms in the mountains, suggesting that geologic change was occurring on Earth

Section 3: Theory of Natural Selection

Artificial Selection Natural variation exists in all populations & some variation is heritable, meaning it can be passed from one generation to the next For 100s of years, humans have been using artificial selection - the process by which humans change a species by breeding it for certain traits Darwin believed that a process similar to artificial selection could happen in nature

Darwin Publishes his Theory Over 20 years after Darwin’s voyage on the Beagle, he received a short essay from Alfred Russel Wallace that summarized all of Darwin’s thoughts about evolution. This prompted Darwin to publish his own book called On the Origin of Species by Means of Natural Selection. Natural Selection is the mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals

4 Main Principles of Natural Selection 1.Variation - natural genetic variation exists in all populations 2.Overproduction - populations tend to produce more offspring than the environment can sustain, leading to competition for resources

3.Adaptation - some variations allow an individual to better survive & reproduce Fitness is a measure of the ability to survive and produce more offspring relative to other members of the population 4.Descent with modification - Over time, natural selection results in changes in a population, as only those with the highest fitness will pass on their genes

Natural Selection acts on Phenotypes Natural selection doesn’t create new alleles, genetic mutations do Natural selection can only act on traits that already exist in a population As an environment changes, different traits become beneficial

Section 4: Evidence of Evolution

Darwin’s Evidence The most important & convincing evidence of evolution comes from fossils, geography, embryology, & anatomy Fossils - fossil organisms in lower, older layers of rock are more primitive than those in upper, newer layers; this supports descent with modification

Geography - Darwin observed that certain plants & animals in the Galapagos Islands were similar but not identical to mainland species He hypothesized that some individuals from the mainland migrated to the islands & then adapted to each particular island

Embryology - similar features of embryos in very different organisms suggests evolution from a distant common ancestor Ex. vertebrate embryos all have gill slits as embryos, but not as adults

Anatomy - comparing body parts of different species provides evidence of evolution Homologous structures are features that are similar in structure but appear in different organisms & have different functions (suggest a common ancestor) Analogous structures are structures that perform a similar function but are not similar in origin; they arise due to similar environmental challenges, not common ancestry

Structural Patterns & Evolutionary History Structural patterns are clues to the history of a species Vestigial structures are remnants of organs or structures that had a function in an early ancestor, but serve little or no function in the present Ex. pelvic bones & hind limb bones in snakes Ex. appendix & tail bone in humans

Section 5: Evolutionary Biology Today

Fossil Record Paleontology was a new science in Darwin’s time Our fossil record is incomplete, but it does support the theory of evolution Many transitional fossils have been found that show the change in organisms over time

Molecular & Genetic Evidence DNA Sequence Analysis - The more related two organisms are, the more similar their DNA will be. Protein Comparisons - Molecular fingerprinting compares similarities among proteins of organisms. Species that have the same proteins most likely come from a common ancestor

Evolution Unites all Fields of Biology All biological fields contribute to evolutionary theory The theory of natural selection along with genetics is sometimes called the modern synthesis of evolutionary theory The basic principles of evolution are used in many scientific fields such as medicine, geology, geography, chemistry