Natural Selection & Evolution

Theory of Evolution Evolution, or change over time, is the process by which modern organisms have descended from ancient organisms. A scientific theory is a well-supported testable explanation of phenomena that have occurred in the natural world.

Before there was Darwin… Lamarck’s Giraffes: Does this make sense? If an organism changes during life in order to adapt to its environment, those changes are passed on to its offspring.

…and then there was Darwin Charles Darwin Trip around the world in 1831 Collected fossil evidence and observations Focused on species of finches and turtles Variety of organisms and variation he saw on his travels sparked his interest in evolution and adaptation

Darwin’s Observations OBSERVATION #1: All species have the potential for the overproduction of offspring.   OBSERVATION #2: Environmental resources are limited. Therefore, only a fraction of offspring are surviving each generation. OBSERVATION #3: No two individuals are exactly alike. OBSERVATION #4: Much of this variation is heritable (passed down through generations).

Theory of Natural Selection 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

Theory of Natural Selection Explains HOW the traits of a population change over time (adaptation) Changes are dependent upon the resources available and pressure from the environment Those individuals with the traits most beneficial for the environment are more likely to EAT, SURVIVE, and REPRODUCE… Eventually, the individual traits become the traits of the population Ex/ all arctic hares are white Video

Amoeba Sisters

Theory of Evolution Natural Selection + Speciation = Evolution Video Process in which new species are created using natural selection and speciation Takes long periods of time for evolution to occur How modern organisms have descended from ancient ancestor Natural Selection + Speciation = Evolution Video

Speciation Creation of new species through adaptation and… Geographical Isolation Separated by land Reproductive Isolation Separated by either mating ritual, mating time, sterility of offspring, habitat or eating habits

Phylogenetic Tree Each branch represents a speciation event Characterized by a new trait Video