Darwin's Theory of Evolution Chapter 15
What is Evolution? • Evolution is….. • Change in a species over time • The process by which modern organisms have descended from ancient organisms • A theory • Well-supported testable explanation (hypothesis) of phenomena that have occurred in the natural world • Used to be called “transmutationism”
Charles Darwin • The major contributor to the theory • Born Feb. 12, 1809 • Same day as Abe Lincoln! • Theology major in college • Religion • Competitor • Alfred Wallace • Published work on natural selection before Darwin • Very Controversial character
Darwin’s Expedition • H.M.S. Beagle • Darwin took a trip around the world on a ship • Like a vacation • Went ashore when the ship ported • Gathered animals and other evidence for his ideas • Galapagos Islands • Main area of collection and influence on his work • 1000 km west of South America
What did he find? • Patterns of diversity • Looked at why certain organisms were found in only certain spots • Why did they survive there when others didn’t? • He looked at Galapagos turtles and finches in particular
Influences on Darwin’s Work • James Hutton • Hypothesized that the earth was shaped slowly • This went against the church btw • Charles Lyell • Principles of Geology • Explained how the earth could be changed so drastically over time • Volcanoes, earthquakes, etc. • So… if the earth changes over time, can animals?
Influences on Darwin’s Work • Jean-Baptiste Lamarck • French naturalist studied animals’ ability to adapt • Tendency Toward Perfection • Changing to acquire adaptations to reach a perfect state • Use and Disuse • If an organism doesn’t use a trait, then it’s lost over time • Ie our appendix and coccyx (tail bone) • Inheritance of Acquired Traits • Traits gained can be passed on • Ie if I lift weights my whole life, then my children will look like Arnold
Natural Selection “It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to change.” -Charles Darwin • Survival of the fittest • Fitness: the ability of an individual to survive and reproduce in its specific environment • Those individuals that possess adaptations that help them survive the best, will be the ones that reproduce and pass on their genes.
Evolution of Populations Occurs when there is a change in relative frequency of alleles
Natural Selection and Species Fitness • Overtime, natural selection results in changes in the inherited characteristics of a population. • These changes increase a species fitness (survival rate)
Descent with Modification • Each living species has descended with changes from other species over time • Darwin’s idea
Endosymbiosis Theory • Theory that during the evolution of the cell, one large bacteria cell engulfed another one that became the mitochondria • This is also how they thought the chloroplast evolved as well • They have their own DNA and a double membrane
Darwin’s Postulates 1. Organisms differ; variation is inherited 2. Organisms produce more offspring than survive 3. Organisms compete for resources 4. Organisms with advantages survive to pass those advantages to their children 5. Species alive today are descended with modifications from common ancestors
Evidence of Evolution • Fossil Record • Geographic Distribution of Living Species • Homologous Body structures • Similarities in Embryology
Fossil Record Fossil Record provides evidence that living things have evolved Fossils show the history of life on earth and how different groups of organisms have changed over time
Relative Dating • Can determine a fossil’s relative age • Performed by estimating fossil age compared with that of other fossils • Drawbacks – provides no info about age in years • Index fossil: compares time periods best over a short period of time and a wide geographic range
Absolute dating • Can determine the absolute age in numbers • Is performed by radioactive dating – based on the amount of remaining radioactive isotopes remain • Drawbacks - part of the fossil is destroyed during the test Trilobites: related to snowshoe crab
Geographic Distribution of Living Species • How can animals be similar, but distinctly different? • The ones Darwin saw on the Galapagos islands must have descended from a common ancestor • Animals on different continents in similar environments have similar anatomies (body structures) and behaviors
Convergent Evolution • When species who are not related evolve similarly due to a similar environmental pressures • Sugar glider and the flying squirrel
More Evidence Homologous Body Structures • Structures that have different mature forms but develop from the same embryonic tissues e.g. Wing of bat, human arm, leg of turtle
Analogous Body Structures • There appear to be many structures that are similar because of the function they carry out and in their external appearance. However, these structures differ internally. These species are NOT descended from a common ancestor. For example, wings of bat and butterfly are similar in appearance.
Vestigial Structures • traces of homologous organs in other species • Organ that serves no useful function e.g. Appendix
Evidence Continued Similarities in Embryology • In their early stages of development, chickens, turtles and rats look similar, providing evidence that they shared a common ancestry.
Speciation • Adaptive Radiation • The process in which multiple species adapt and change (evolve) due to different environmental pressures from one common ancestor
How Does Speciation Occur? • Geographic Isolation • Physical barrier separates a population • Behavioral Isolation • Capable of breeding, but are separated by courtship rituals or reproductive strategies • Temporal Isolation • Reproduce at different times
Coevolution • When organisms that are ecologically close -- for example, predators and prey, or hosts and parasites -- influence each other's evolution, we say that coevolution is occurring • One species’ evolution is in response to the other • One example is the bacteria living in our stomachs. They have evolved along with us.
Human Skulls Australopithecus Homo erectus Homo sapien
LigerResult of male lion and female tiger mating in captivity. Offspring are infertile.
Tigon Result of male tiger and female lion mating in captivity. Offspring are infertile.
Extinction • 99% of all species that have ever lived are now extinct