Evolution History and Theory
Theory of evolution • Theories:explanations for facts about natural events supported by many experiments over time • Evolution:change over time • Theory of Evolution: modern organisms descend from ancient organisms • Biological Diversity: the large variety of living things on Earth
Theoretical timeline: 1795 • James Hutton: • Theory of Geological change • Forces change earth’s surface shape • Changes are slow • Earth is much older than thousands of years
Theoretical timeline: 1798 • Thomas Malthus-19th century English economist • Population Growth • If population grew (more births than deaths) • Insufficient living space • Food runs out • Darwin applied this theory to animals/plants
Theoretical timeline: 1830 • Charles Lyell • Book: Principles of Geography • Principle of Uniformitarianism • Geographical features can be built up or torn down • Darwin thought…if earth changed over time, what about life?
Getting closer… 1809 • Jean Baptiste de Lamarck • Was eventually disproved • The first attempt to support evolution • Recognized that living things have changed over time • Realized that organisms are somehow adapted to their environments
Lamarck’s hypothesis • Tendency towards perfection • Ex. Birds kept trying to fly until their wings developed enough for flying • Use and disuse • Ex. Giraffes continuously stretched their necks to reach tree tops, so their necks grew • Inheritance of acquired traits • Ex. The giraffe’s offspring would be born with a longer neck
What’s wrong with lamarck’s theory? • Thought behavior affected heritable traits • Heritable traits: passed down from parent to child through genes • Ex: If a person builds up their muscles, their children will not be born with bigger muscles.
Darwin’s voyage H.m.s. beagle: 1831-1836 • Traveled the world • Made observations • Saw variation within species on different islands • Collected evidence • Plant and animal specimens • Developed hypotheses after returning to England
GalÁpagos islands • Off the coast of South America, near Ecuador • Volcanoes, tortoises, and birds…oh my! • Smaller, low islands were hot, dry, and nearly barren with little vegetation • High islands had greater rainfall, an assortment of animals, and rich vegetation.
Tortoises… varied from one island to another. The shape of the shell could be used to identify which island it inhabited.
Darwin’s Finches • 14 species of finches with one common ancestor • Variety of beak adaptationsdue to isolation of populations on different islands • Struggle for existence: ongoing competition for resources
Darwin’s Theory: natural selection • Parent organisms reproduce similar offspring • Heritable variation is caused by variations in an organisms genes. • In most species, only a small percentage will survive to reproduce, depending on… • Fitness: how well an organism can survive in its environment • Survival of the fittest: individuals better suited to the environment, and are more likely to survive/reproduce. • Adaptations are inherited characteristics that increase an organism’s chance for survival. • Over many successive generations, natural selection changes characteristics of a population
Natural selection Requires • Variations in traits within a population • Ex. Length of giraffes’ necks • More individuals are born than can survive • Ex. Struggle for existence…someone’s gottago! • 3. Individuals with greater fitness get more resources, survive, and reproduce. • Ex. Giraffes with naturally long necks get more food, survive, and have babies with long necks (trait passed on in genes) • 4. Over time and many generations, traits in the population change. • Ex. average neck length of the population increases.
Critical thinking Answer on a separate piece of paper and hand in to the basket. p. 386, Key Concept #2 p. 389, #1-4, 6, 8, 10, 12, 15, 18, 19 p. 390, #30