Darwin Chapter 22

Charles Darwin Lived in England 1809-1882 1831-1836: Beagle’s five-year voyage mapping the coastline of South America 1859: On the Origin of Species by Means of Natural Selection EVOLUTION  explains how modern organisms evolved over long periods of time through descent from common ancestors 

On the Origin of Species by means of Natural Selection Published by Darwin in 1859 (158 years ago) Two major claims: The species present on Earth today descended from ancestral species Natural selection is the mechanism for evolution Natural Selection leads to evolutionary adaptation. Individuals with beneficial heritable traits leave more offspring, therefore, the frequency of those traits increases in the population over generation Evolution – changes in a population’s genetic composition over time.

Darwin challenged traditional views Prevailing view = Earth was only a few thousand years old, species of organisms were unchanging, created by God

Historical context Aristotle (384-322 B.C.) – all living forms could be arranged on a scale of increasing complexity = scala naturae species are permanent and perfect and do not evolve Natural Theology – 1700s Based on Old Testament creation story Species were individually designed by God and do not evolve Taxonomy = science of classification Sought to classify the species that God had created Linnaeus (1707-1778) – taxonomy showed God’s organization

Historical context (continued) Georges Cuvier (1769-1832): paleontologist; felt changes in fossils at different strata due to catastrophism. Some catastrophe (flood or drought) destroyed large numbers of species at a time Hutton: (1726-1797): gradualism; profound change can take place through the cumulative effect of slow but continuous processes. Earth’s geologic features explained by mechanisms currently operating in the world.

Historical context (continued) Charles Lyell (1797-1875): uniformitarianism; basic geological processes (wind, rain, erosion, etc.) have not changed throughout Earth’s history. Darwin reasoned that Earth must be older than 6000 years

Other scientists suggest that evolution occurs Lamarck’s theory of evolution: theory of evolution based on the idea that modification acquired during life of an organism passed to offspring. Wallace: also developed theory of evolution based on natural selection in1858; this pushed Darwin to publish his findings

Acquired Characteristics Inherited Characteristics List the characteristics that you believe you have always had. For example, you may have brown eyes or curly hair. List your acquired characteristics. For example, you may have learned how to play a musical instrument.

Lamarck’s Evolutionary Hypothesis Jean Baptiste Lamarck – proposed theory of evolution based on growing fossil record Suggested that organisms could change during their lifetimes by selectively using or not using various parts of their bodies. Suggested that individuals could pass these acquired traits onto offspring, enabling species to change over time Published ideas in 1809 – year Darwin was born Lamarck proposed that all organisms have an inborn urge to become more complex and perfect, and to change and acquire features that help them live more successfully in their environments. Lamarck thought that organisms could change the size or shape of their organs by using their bodies in new ways. Traits altered by an individual organism during its life are called acquired characteristics. .

Evaluating Lamarck’s Hypothesis Lamarck was INCORRECT because: Organisms do not have an inborn drive to be perfect Evolution does not mean that over time species becomes “better” somehow Evolution does not progress in predetermined direction Traits acquired by organisms during lifetime cannot be passed on to offspring Lamarck gave us some good stuff too! Lamarck was one of 1st to try to explain evolution scientifically using natural processes Recognized link b/w org’s environment and body structures

Darwin’s research Charles Darwin (1809-1882) Voyage of the HMS Beagle – 1831 mission to chart the South American coastline Observations: Adaptations of plants and animals were similar in similar environments Geologic change (for example due to earthquake) indicated that Earth was much older than 6000 years. Geographic distribution of unusual species on Galapagos indicated descent with modification

Blue Footed Boobies

Artificial Selection Artificial Selection: selective breeding of domesticated plants and animals to produce offspring with genetic traits that humans value nature provides variation, humans select variations that are useful. Example: a farmer breeds only his best livestock

Artificial Selection Humans have been modifying species for thousands of years Darwin saw this being done with dogs He observed that a species could be changed a lot in a short period of time Thought that the same thing could be happening in nature at a slower pace

Differences Natural Selection Artificial Selection Traits that are more beneficial in the organisms environment become more common in the population Humans choose the traits that become more common in the population

What Darwin Knew What did Darwin (and science) know? The Earth is REALLY old 4.6 Billion Years The Earth has changed over time Mountains and valleys formed Rivers change course Water erodes land Humans can change organisms through breeding Organisms have rapid Population Growth Darwin realized most organisms don’t survive and reproduce… ???Which individuals survive and why???

What Darwin didn’t know DNA and Genetics Knew that traits were passed from parent to offspring Didn’t know HOW

POGIL

Struggle for Existence If more individuals are produced than can survive  members of a population must compete to obtain food, living space, and other limited necessities of life Called: Struggle for Existence Which individuals come out on top of struggle?

Variation and Adaptation Individuals have natural variations among heritable traits Some variants are better suited to life in their environment than others Predatory species that are faster, longer claws, sharper teeth  catch more prey Prey species that are faster, better camouflaged  avoid being caught

Some Variations are Favorable Adaptation - any heritable characteristic that increases an organism’s ability to survive and reproduce Body parts or structures bear’s claws body color  camouflage or mimicry Physiological functions a plant carrying out photosynthesis Behaviors avoidance strategies prey use crane flapping wings

Darwin’s Theory of Natural Selection Animals on different islands are in different populations Galapagos Islands were most likely colonized by a single finch species from South America Single species adapted to the varied habitats on the islands Today we have 13 different species of finch Differ by Beak Shape WHY?

Darwin’s Observations Overproduction Variation Based on Malthus’ Idea, Darwin realized that species tend to produce excess offspring limit resources + excess offspring = competition Not Everyone Survives! Differences among members of the same species Most variation is heritable Siblings look more like each other than they do other people

Darwin’s Observations

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

Summary of Darwin’s Theory The Process Organisms differ; variation is inherited Organisms produce more offspring than survive Organisms compete for resources Organisms with advantages survive to pass those advantages to their children Species alive today are descended with modifications from common ancestors

Summary of Darwin’s ideas Natural selection refers to the differential success in reproduction which results in adaptations of populations of organisms to their environment Natural selection occurs from the interaction between the environment and the inherent variability in a population Variations in a population arise by chance Natural selection is not a chance phenomenon, since environmental factors set definite criteria for reproductive success