7.1 Darwin’s Theory

Key ideas What important observations did Darwin make on his voyage? How did Darwin account for the diversity of species and the differences between similar species? How does natural selection lead to evolution?

Darwin’s Observations December 1831, Charles Darwin set sail from England on a five year trip around the world. He observed plants and animals he had never seen before. This observation led him to develop the theory of evolution by natural selection.

Darwin’s observations included: Diversity of organisms Species: a group of similar organisms that can mate with each other and produce fertile offspring Remains of ancient organisms (fossils) Fossil: preserved remains or traces of an organism that lived in the past Characteristics of organisms on the Galapagos Islands

Examples of different species.

Fossils

Comparisons to South American Organisms How are these iguanas different?

Galapagos Organisms Darwin’s drawings Identify some specific differences in these finches’ beaks. These finches live in different islands.

Adaptations Def: a trait that helps an organism survive and reproduce in its environment. Ex: milkweed – poisonous or have a bad taste – avoid being eaten Ex: some plants have bright colored flowers – attract insects

Evolution Darwin reasoned that plants or animals that arrived on the GI faced environmental factors that were different from those on the mainland. Darwin hypothesized that the species gradually changed (evolution) over many generations and became better adapted to the new environments.

Scientific theory Scienfic theory: A well-tested concept that explains a wide range of observations Darwin concluded that organisms on the GI had changed over time, but did not know HOW the changes had happened.

Selective Breeding Humans have used selective breeding to produce sheep and pigeons that fit certain criteria. Darwin thought that a process similar to selective breeding might happen in nature.. But what process would push this selective breeding in nature?

Meet the Supercow □ at 3:30

Natural Selection Darwin proposed that evolution occurs in nature through natural selection ( individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species) in the book called, On the Origin of Species by Natural Selection.

Overproduction – Malthus pointed out that sometimes the food supply is not large enough to feed all the offspring of certain organisms- insects, humans, etc. Darwin knew that overproduction occurs in many species. Why don’t all the offspring survive?

Genetic Variations: a difference between individuals of the same species Certain insects may be able to eat foods that others might avoid This characteristic gives the insects an advantage over others.

Competetion – since food and other resources are limited, the members of a species must compete with each other to survive. Selection – some variations make individuals better adapted to their environment making them more likely to survive and reproduce

Selection cont’d – Darwin proposed that, over a long time, natural selection can lead to change. Helpful variations may gradually accumulate in a species, while unfavorable ones may disappear.

Environmental factors - factors in the environment can affect an organisms’s ability to survive. Genes and natural selection – like environmental factors, genetic variation contributes to evolution. Without variations, all members of a species would have the same traits.

Why the big eyes??

NOT EVOLUTION… human manipulation.

Darwin could not explain what caused variations or how they were passed on. Scientists later learned that variations can result from mutation and the shuffling of alleles during meiosis. Genes are passed from parents to offspring. Because of this, only traits that are inherited, or controlled by genes, can be acted upon by natural selection