How do living things vary?

Over time, the number of organisms with a trait that helps them survive or reproduce will increase in a population.

What makes some organisms more likely to live to adulthood?

What is different about them?

Could it have something to do with their traits?

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

Charles Darwin

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

Darwin was amazed by the tremendous diversity, or variety of living things he saw on his voyage.

Argentina Galapagos Islands

Giant Tortoise

Iguana

He wondered why there were so different from those in England.

Armadillo found in Argentina

Armadillo found in Texas

Observations of diversity

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.

Hmmm…

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. Overproduction2. Genetic variation3. Struggle to Survive4. Successful reproduction

Over production

Organisms often have more offspring than will survive long enough to become adults.

Tarantula egg sack

Genetic Variation

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.

No two individuals in a population are exactly alike.

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 reproductionOrganisms 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 MothIn the early 1800’s scientists found that most of the peppered moths in England were light colored. Dark colored moths were rare.

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.

England, Early 1800’s

Environmental changes alter the peppered moth population

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.

England 1850’s

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.

Environmental

Issues

Selective Breeding

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

Selective breedingSummary: 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