How do living things vary? What makes some organisms more likely to live to adulthood? What is different about them? Could it have something to do with their traits? Over time, the number of organisms with a trait that helps them survive or reproduce will increase in a population.

Charles Darwin Darwin’s observations led him to develop a scientific theory that is known as the theory of evolution by natural selection.

Replica of the HMS Beagle Darwin’s Voyage In December 1831, the British naval ship HMS Beagle set sail from England . On board was 22-year-old scientist Charles Darwin. His mission was to learn as much as he could about the living things he observed on his trip around the world. Replica of the HMS Beagle

Darwin’s Observations Giant Tortoise Darwin was amazed by the tremendous diversity, or variety of living things he saw on his voyage. Argentina Galapagos Islands He wondered why there were so different from those in England. Iguana

Armadillo found in Argentina Armadillo found in Texas

Observations of diversity Hmmm… Today scientists know that living things are even more diverse than Darwin could ever have imagined. Scientists have identified more than 1.7 million species of organisms on Earth. A species is a group of similar organisms that can mate with each other and produce fertile offspring.

There are more than 35,000 known species of spiders, including over 800 tarantula species.

Natural Selection Natural selection is changes in genetic traits over many generations (the process by which individuals with favorable traits survive and reproduce). Darwin’s theory of natural selection can be described in four basic steps: 1. Overproduction 2. Genetic variation 3. Struggle to Survive 4. Successful reproduction

Over production Organisms often have more offspring than will survive long enough to become adults. Tarantula egg sack

Genetic Variation No two individuals in a population are exactly alike. Every individual has its own combination of physical traits. Some of these traits improve survival and other traits lower the chances of survival in it’s environment.

Struggle to survive Individuals in a population must compete for food, water, living space, and mates. Some individuals may be killed by predators, or by diseases. Tarantula hawk

Successful reproduction Organisms must reproduce to pass their genes to the next generation.

Watching Natural Selection happen Populations are always responding to changes in their environment. Whether a new predator moves into an area or the climate changes, some individuals will be better able to adapt than others. These individuals will be more likely to pass their traits to future generations.

Natural Selection and the Peppered Moth In the early 1800’s scientists found that most of the peppered moths in England were light colored. Dark colored moths were rare. England, Early 1800’s The bark on the trees in Europe at the time were light colored. The light colored moths were hard to see. The dark peppered moths were easy to see.

Environmental changes alter the peppered moth population England 1850’s During the 1850’s, the environment in Europe began to change. Thousands of factories began to burn coal and fill the air with smoke and dark soot. The bark on the trees in Europe at this time began to become darker. The dark colored moths were hard to see. The light colored moths were easy to see. Birds began to eat more light colored moths because they were easy to find.

Environmental Issues Pollution can affect human lives as well as the lives of other living things. Smog has killed large numbers of people since the industrial revolution. In 1952, nearly 4,000 people were killed when a heavy smog hung over London.

Selective Breeding the breeding of parent organisms by man to produce desires traits in the next generation

Selective breeding Domestic Animals Plants: Summary: Human Influence on characteristics and behavior. Domestic Animals Ex: Chickens, Dogs, Cows Plants: Ex: Corn, Brasilica, Fruit hybrids

Evolution of the whale http://www.pbs.org/wgbh/evolution/library/03/4/l_034_05.html