Theory of Natural Selection Chapter 15 Section 1

Learning Targets I can… Explain the biological definition of evolution Discuss Darwin’s principle of survival of the fittest and explain what Darwin meant by natural selection

Developing the Theory Charles Darwin – “The Father of Evolution” Darwin boarded the HMS Beagle in 1831 to survey the coast of South America Darwin was a naturalist and companion to the captain His job was to collect biological and geological specimens during the ship’s travels

Developing the Theory In 1835 the HMS Beagle arrived at the Galapagos Islands Darwin began to collect mockingbirds, finches, and other animals on the four islands he visited Noticed that different islands seemed to have their own, slightly different varieties of animals.

Developing the Theory

Developing the Theory After Darwin returned to England, he reconsidered his observations He determined that almost every specimen brought from the islands was new to European scientists The specimens did resemble specimens on the main land of South America, though they were not identical

Developing the Theory

Developing the Theory Darwin hypothesized that new species could appear gradually through small changes in ancestral species, but wasn’t sure how this could work - So, he turned to animal breeders to get a better understanding

Developing the Theory Darwin learned that breeders use Artificial Selection Artificial Selection is where a breeder can promote traits that are beneficial to the species or work to remove traits that are not beneficial Can also result in developing new breeds of dogs or new strains of crop plants, etc.

Developing the Theory While thinking of Artificial Selection , Darwin read an essay by the economist Thomas Malthus The essay suggested that the human population, if unchecked, eventually would outgrow its food supply, leading to a competitive struggle for existence Darwin realized that Malthus’ ideas could be applied to the natural world.

The Theory of Natural Selection Darwin then proposed his Theory of Natural Selection, which had 4 principles: Individuals in a population show variations among others of the same species Example: No single zebra has the same stripes as another

Theory of Natural Selection Variations are inherited Ex: Children look similar to parents Animals have more young than can survive on available resources Ex: Cardinals lay 9 eggs (on avg.) per summer. If each cardinal lived only one year, in seven years there would be a million cardinals if all offspring survived.

Theory of Natural Selection Variations that increase reproductive success will be more common in the next generation - ex: If having a fan-shaped tail increases reproductive success of pigeons, then more pigeons in the next generation will have fan-shaped tails.

The Origin of Species It is believed that Darwin’s theory originated near 1840 Soon after he began writing a multi-volume book compiling evidence for evolution and explaining how natural selection provides a mechanism for the origin of species

The Origin of Species Darwin eventually published his book “ On the Origin of Species by Means of Natural Selection” In his book, Darwin used the term evolution only on the last page. Today, biologists use the term evolution to define cumulative changes in groups of organisms through time

Evolution Darwin’s theory of natural selection is not synonymous with evolution It is a means of explaining how evolution works

Explore the Galapagos Go to the website http://www.pbs.org/wgbh/nova/evolution/explore-galapagos.html Complete the questions on the packet for #1 – 10. Then complete the diagram question on the back of the packet