Darwin’s Idea for Natural Selection By Kristi Schramm

Open your books to page 378  Read “Publication of ‘On the origin of Species” –Summarize in 3-4 sentences  Read ‘Inherited Variation and Artificial Selection’ –Summarize in 3-4 sentences

Darwin’s Influences  Darwin studied many scientific theories of his time  Scientists that influenced Darwin’s later theories include Hutton, Lyell, Lamarck and Malthus

James Hutton and Charles Lyell  Theory: The earth is many millions of years old and that the same processes that shaped the earth millions of years ago are the same as today  Made Darwin wonder: –If the Earth could change over time, might life change over time? –This change would only be possible if the earth was extremely old

Jean-Baptiste Lamarck  Noticed that animals were “adapt” to their environment  Theory: Acquired Characteristics: the use or disuse of a body part during it’s lifetime would effect how traits were passed onto the offspring.  Made Darwin wonder: –How did parents pass on their traits (inheritance) –Why are organisms so well adapted to their environment?

Thomas Malthus  Observation: Babies are being born more than people are dying.  Theory: if the human population continued to grow unchecked, eventually there would not be enough food or living space for everyone.  Influenced Darwin: Organisms give birth to many more offspring than can survive and reproduce

Write these questions in the Cornell Notes section (on the left)  What did Darwin observe in the Galapagos Islands?  When did Darwin publish his ideas?  What is Artificial Selection?

Darwin Presents His Case  Darwin studies his specimens from the Galapagos  The wrens, warblers, and blackbirds he thought he found were all actually finches!

Darwin Presents His Case  After 25 years of mulling over his theories, Darwin receives a document from Alfred Wallace summarizing the exact theory Darwin came up with

Darwin Presents His Case  Published his book in 1859  Artificial Selection: Humans breed the species with the most desired variations to enhance the desired trait.  Ex: Dog Breeding

Darwin’s Theory of Evolution by Natural Selection  Natural Selection is a process that allows the evolution of species over time  Darwin stated that three things must be true for natural selection to occur: –Struggle for Existence –Survival of the Fittest –Descent with modification

Struggle for Existence  Based on Malthus’s work populations Darwin’s theory states that there must be a struggle for existence. Not all offspring can survive because, there is competition for food, living space and other necessities of life.

Survival of the Fittest  Fitness= ability to survive and successfully reproduce  Higher fitness is a result of organisms that have characteristics that help them better survive in their environment. (These characteristics are called adaptations)  Organisms with more beneficial characteristics (phenotypes) will survive better.

Descent with Modification  Species today look different from species long ago (fossil record)  Natural selection will act on phenotypic variations that allow organisms that occupy different niches. By occupying a different niche some of the variation is an adaptation to one niche, while a different variation could be an adaptation to another niche.

Variation in beak type made the birds more suited for different niches.

 Implies that all species are related to one another (common descent)  Each living species has descended with changes from other species –How do you think these changes arose?  Mutations Descent with Modification

Evidence of Evolution Darwin argued that life on earth has been evolving for millions of years.  The Fossil Record  Geographic Distribution of Living Species  Homologous Body Structures  Similarities in Early Development

The Fossil Record  Showed that: –There have been countless species that have lived on earth but no longer live on earth today –Layers of rocks with fossils (ancient life) demonstrated that thousands, or even millions of years were needed to create this

The Fossil Record

Geographic Distribution of Living Species  Animals that are related to each other showed ‘decent with modification.’ Organisms had modifications that varied based on the environment they lived in  Animals that were not related each other looked similar if they were from similar environments. Beaver Muskrat Capybara

Geographic Distribution of Living Species Desert FoxKoala Dingo Example: Based on what they look like: Which two animals do you think are more closely related to one another?

Geographic Distribution of Living Species Desert FoxDingo Are not related to each other even though they look more alike. Evolutionists say they look alike because they live in the same kind of environment so over time they adapted in similar ways

Homologous Structures  Arms, wings, legs, and flippers all have very similar bones  Darwin believed this was evidence that all species were original descended from one common ancestor.

Similarities in Early Development Looking at the embryonic development of organisms Darwin noticed some similarities that other scientists also noticed.