Charles Darwin, 1831, at 22 years old•Was sent on a 5 year trip around the world by ship•He learned as much as he could about the organisms he saw on the trip.

He saw and thought about….

• Differences between the organisms on each island• Differences between the organisms

on the Islands and the Mainland• Differences between the organisms

on the Islands and in England

Differences Between IslandsDifferences Between IslandsPointed and Smooth Shells,Bird Varieties

Differences between the organisms on the Islands and the Mainland nearby• Genetic Difference between Galapagos and

South American Yellow Finches.

Organisms different from those studied at home

Galapagos and England Doves

More Diversity1.7 million species of organisms identified on EarthGrizzly Bear here AND Panda and Polar elsewhereCalifornia King Snake, Western Rattlesnake,California Redwood, California Bay Laurel TreeCalifornia Bay Laurel, Valley Oak

Darwin was amazed at this diversity• He noticed that iguanas that lived in trees and ate

leaves on the mainland had smaller claws.• He noticed that iguanas with larger claws were able

to grip the slippery rocks of the Galapagos Islands.

More and More Differences• He also saw differences in the pointed or smooth tortoise

shells between the islands

• He saw differences in the color of the Finches in South America and on the islands

• He saw differences in the color of the Doves on the Islands and those from his home

His observations led him to develop a theory

Darwin wondered why there were these differences and variations

• Darwin hypothesized that a small number of species came to the islands by floating on a log…

• Once there, they reproduced and their offspring became different from their mainland relatives.

Differences to Adaptations

The differences Darwin noticed are examples of ADAPTATIONS

An adaptation is a trait that helps an organism survive and reproduce in its environment.

• Some adaptations keep organisms from being eaten.

• Some adaptations aid in reproduction:the color of flower petals attract pollinators.Darwin wanted to understand adaptations better!!

After 20 years of thinking

Darwin reasoned that:• Plants and animals that arrived on the Islands

faced new environmental factors than those on the mainland.

• He hypothesized that the species gradually changed over many generations and became better adapted to the new environment.

• This gradual change in a species over time is called evolution.

Darwin’s ideas are often referred to as the theory of evolution.

A theory is not a casual thought or a hypothesis.

• A scientific theory is a well-tested concept that explains a wide range of observations.

From the evidence he gathered,

Darwin concluded that organisms on the Galapagos Islands are changing over time.

“On the Origin of Species by Natural Selection”

was published by Darwin 28 years after his trip.

In it, Darwin proposed that:Evolution occurs in nature through a mechanism

called Natural SelectionIn Natural Selection: Individuals that are better adapted to their

environment are more likely to survive and reproduce than other members of the same species.

Factors that affect the process of Natural Selection

1. Overproduction2. Genetic Variation:A difference betweenindividuals of thesame species

3. Competition

Selection• Some variations make individuals better adapted

to their environment.

• Those individuals are more likely to survive, and reproduce.

• The offspring may inherit the helpful characteristics, making the offspring more likely to survive and reproduce, and pass on those characteristics to their offspring……….

Results of Selection• After many generations, more members of the

species will have the helpful characteristic.• The environment has selected organisms with

helpful traits to become parents of the next generation.

• Over time, Natural selection canlead to change.

• Helpful variations may gradually accumulate, and

• Unfavorable variations may disappear.

Environmental Factors• Environmental factors can affect

an organisms ability to survive.• Environmental factors can

therefore lead to selection.For Example:

• With a change in the environment, some individuals may be able to survive in the new conditions. These individuals will grow and reproduce.

Genes and Natural Selection

• Genetic variation also leads to selection.• Without variations, all members of a species

would have the same traits.So….

• Natural Selection would not occur because all individuals would have an equal chance of surviving and reproducing.

Inherited Traits and Natural Selection

• Variations can result from mutations and 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.