Chapter 6 Section 1: Darwin’s theory Key concepts: What important observations did Darwin make on his voyage? What hypothesis did Darwin make to explain the differences between similar species? How does natural selection lead to evolution? Key terms: species, fossil, adaptation, evolution, scientific theory, natural selection, variation.

Chapter 6 section 1: Darwin’s theory Darwin – took the HMS Beagle from England on a 5 year trip around the world. He was the ships “naturalist” – a person who studies the natural world.

Darwin’s important observations Included the diversity of living things, the remains of ancient organisms, and the characteristics of organisms on the Galapagos Islands

Darwin Diversity – Darwin was amazed by the diversity of living creatures that he saw Species – a group of similar organisms that can mate with each other and produce fertile offspring Fossils –the preserved remains or traces of an organism that lived in the past.

Galapagos In 1835 the Beagle reached he Galapagos Islands (West of South America) Darwin found many similarities between the organisms on the islands and those in South America, but there were important differences From his observations, Darwin hypothesized that the animals had originally come from South America and had ADAPTED to the environment on the island (by getting larger claws, or different beaks, or other methods to help the animals survive on the island)

What’s important about this? Ummmmmm Animals adapted over many generations to eat and live better on the island, meaning they passed on NEW genetic traits to their offspring. Animals, Darwin believed, were evolving to adapt to the island.

Comparisons among the Islands Darwin noticed differences between the different islands. For example, tortoises on one island had dome shaped shells. On another island, they had saddle shaped shells.

Adaptations Like the tortoises, finches on the Galapagos Islands were noticeably different from one island to the next, especially the beaks of the finches. Beak shape is an example of an adaptation, a trait that helps an organism survive and reproduce. Certain beak structures helped finches get food. Some plants became poisonous or developed a bad taste to prevent animals from eating them.

Evolution Darwin spent the next 20 years consulting other scientists. His reasoning: Darwin reasoned that plants or animals that arrived on the Galapagos Islands faced conditions that were different from those on the mainland. Perhaps, Darwin hypothesized, the species gradually changed over many generations and became better adapted to the new conditions. This gradual change over time is called evolution.

Scientific theory (from an earlier chapter, but also in this chapter): a well-tested concept that explains a wide range of observations (tells the how and why) Selective breeding: Darwin studied other examples of breeding to help him understand evolution. For example, farmers would breed sheep with fine wool together to produce offspring with similar traits. This is called selective breeding.

Natural selection In 1858 – Darwin and another scientist, Alfred Russell Wallace, each proposed an explanation for evolution. In his book, The Origin of Species, Darwin proposed that evolution occurs by “natural selection”.

Natural Selection Natural selection is the process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species. Darwin identified factors that affect the process of natural selection: OVERPRODUCTION, COMPETITION, AND VARIATIONS.

Overproduction Darwin knew that most species produce far more offspring than can possibly survive. For example, female insects will lay thousands of eggs. If all newly hatched insects survived, they would crowd out all other plants and animals. This does not happen, why not?

Variations Any difference between individuals of the same species is called a variation.

Competition Food and other resources are limited, so members of a species must compete with each other to survive. It does not always involve direct physical contact (fighting). Most competition is indirect (not finding enough to eat).

Selection Darwin observed that some variations make individuals better adapted to their environments. Those individuals are more likely to survive and reproduce. Their offspring will likely inherit the helpful characteristic. After many generations, more members of the species will have the helpful characteristic.

Natural selection (again) 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 change A change in the environment can affect an organism’s ability to survive. The environmental change can therefore lead to selection. For example: Monkey flowers are a type of plant. They cannot grow in a soil with high concentration of Copper. However, because of genetic variation, SOME varieties now grow near copper mines, despite the copper in the soil.

How did zat happen? Welll..

Monkey flowers When the soil around a mine first became contaminated, a small number of monkey flower plants may have been able to survive. These grew and reproduced. After many generations, most of the seeds that sprouted in the soil produced monkey flowers that could withstand the copper.

Genes and natural selection Without variation, all members of a species would have the same traits. Natural selection would not occur because all individuals would have an equal chance of surviving and reproducing. Where do variations come from? Mutations, gene exchange during meiosis