10.2 Darwin’s Observations 10.1 Early scientists proposed ideas about evolution before Darwin. Evolution is the biological change over time by which descendants come to differ from ancestors. A species is a group of organisms that can reproduce and have fertile offspring.

10.2 Darwin’s Observations Evolution of a horse

10.2 Darwin’s Observations Theories of geologic change set the stage for Darwin’s theory. There were three theories of geologic change: – Catastrophism: natural disasters such as floods and volcanic eruptions have shaped landforms and caused species to become extinct. – Gradualism: changes in landforms resulted from slow changes over a long period of time – Uniformitarianism: the geologic processes that shape Earth are uniform through time

10.2 Darwin’s Observations

10.1 – Evolution – – Life in a 24 hour day. 2 min – Turn & Talk assignment: Try to list as many events as you can in the 24 hour day, then compare with your partner to see if you captured all of the events.

10.2 Darwin’s Observations 10.2 Darwin observed differences among island species. Variation is a difference in a physical trait. – Galápagos tortoises that live in areas with tall plants have long necks and legs. Those with short necks lived in areas with low plants. – Galápagos finches that live in areas with hard-shelled nuts have strong beaks. Those that lived where fruit and insects were found had long, thin breaks.

10.2 Darwin’s Observations

An adaptations is a feature that allow an organism to better survive in its environment. –Species are able to adapt to their environment. –Adaptations can lead to genetic change in a population.

10.2 Darwin’s Observations Darwin found fossil evidence: of extinct animals that resemble modern animals. Darwin observed fossil and geologic evidence supporting an ancient Earth.

10.2 Darwin’s Observations Geological Evidence: He saw land move from underwater to above sea level due to an earthquake.

10.2 Darwin’s Observations 10.3 KEY CONCEPT Darwin proposed natural selection as a mechanism for evolution.

10.2 Darwin’s Observations Several key insights led to Darwin ’ s idea for natural selection. Darwin noticed a lot of variation in domesticated plants and animals. Artificial selection is the process by which humans select traits through breeding. neck feathers crop tail feathers

10.2 Darwin’s Observations Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals. Heritability is the ability of a trait to be passed down. There is a struggle for survival due to overpopulation and limited resources.

10.2 Darwin’s Observations

Natural selection explains how evolution can occur. Variation: heritable differences that exist in every population are the basis for natural selection Overproduction: Having many offspring increases the chance of survival but also results in competition for resources Adaptation: certain variation that allows an individual to survive & reproduce better than other individuals it competes against – Fitness: ability to survive and reproduce Descent with modification: Heritability of adaptations. More individuals will have the trait in every following generation, as long as the environmental conditions remain beneficial for the trait

10.2 Darwin’s Observations _M _M (First half of above video) Natural Selection: Crash Course 6 min

10.2 Darwin’s Observations 10.4 KEY CONCEPT Evidence of common ancestry among species comes from many sources.

10.2 Darwin’s Observations Fossils & the Fossil Record Shows how species changed their form/shape over time Ways of dating fossils: – Relative dating: estimates the age of fossils by comparing fossil to others in the same layer of rock Pro: can be used if there is no other way to tell the age of the fossil Con: layers of rock can be shifted by natural events (earthquakes, mudslides, etc.) and this can mess up estimate – Radiometric dating: uses the decay of radioactive isotopes (carbon-14 changes into nitrogen-14) Pro: can give an accurate age Con: can’t give an age for really old fossils (if all isotopes have decayed)

10.2 Darwin’s Observations The study of geography provides evidence of evolution. –island species most closely resemble nearest mainland species –populations can show variation from one island to another

10.2 Darwin’s Observations Embryology Similar embryos, diverse organisms Identical larvae, diverse adult body forms Gill slits and “tails” as embryos Larva Adult barnacle Adult crab

10.2 Darwin’s Observations

Homologous Structures Similar in structure, different in function Evidence of a common ancestor Example: bones in the forelimbs of different animals (humans, cat legs, whale fins, bat wings) Anatomy: Uses body structure as evidence of evolution.

10.2 Darwin’s Observations Vestigial structures are remnants of organs or structures that had a function in an early ancestor. Ostrich wings are examples of vestigial structures. Structural patterns are clues to the history of a species.

10.2 Darwin’s Observations Human hand Bat wing Mole foot Fly wing – Analogous structures are not evidence of a common ancestor. –Analogous structures have a similar function.

10.2 Darwin’s Observations Molecular Biology Common (universal) genetic code (A, T, C, & G) Similarities in DNA, proteins, genes, & gene products Two closely related organisms will have similar DNA sequences & proteins

10.2 Darwin’s Observations

DNA fingerprints will also be very close if the species are closely related

10.2 Darwin’s Observations 1oQ8 1oQ8 Start at 3 minutes (Evidence of Evolution) 6 min