p. 079 Natural Selection

species

A group of similar organisms that can breed and produce fertile offspring.

natural selection

A natural process resulting in the evolution of organisms best adapted to the environment.

adaptation

A trait that helps an organism survive and reproduce

Common Ancestor

An ancestral species from which later species evolved

Overproduction

Strategy in which organisms make more offspring than will actually survive.

Fitness

the ability of an individual to survive and reproduce in a particular environment

Alfred Russel Wallace

Alfred Russel Wallace OM FRS (8 January 1823 - 7 November 1913) was a British naturalist, explorer, geographer, anthropologist, and biologist.[1] He is best known for independently conceiving the theory of evolution through natural selection; his paper on the subject was jointly published with some of Charles Darwin's writings in 1858.[2] This prompted Darwin to publish his own ideas in On the Origin of Species. Wallace did extensive fieldwork, first in the Amazon River basin and then in the Malay Archipelago, where he identified the faunal divide now termed the Wallace Line, which separates the Indonesian archipelago into two distinct parts: a western portion in which the animals are largely of Asian origin, and an eastern portion where the fauna reflect Australasia.

evolution

Change in a kind of organism over time; process by which modern organisms have descended from ancient organisms.

Charles Darwin's Story

Darwin's Theory The Englishman Charles Darwin is one of the most famous scientists who ever lived. His place in the history of science is well deserved. Darwin's theory of evolution represents a giant leap in human understanding. It explains and unifies all of biology. Darwin's theory of evolution actually contains two major ideas: One idea is that evolution occurs. In other words, organisms change over time. Life on Earth has changed as descendants diverged from common ancestors in the past. The other idea is that evolution occurs by natural selection. Natural selection is the process that results in living things with beneficial traits producing more offspring than others. This results in changes in the traits of living things over time. In Darwin's day, most people believed that all species were created at the same time and remained unchanged thereafter. They also believed that Earth was only about 6,000 years old. Therefore, Darwin's ideas revolutionized biology. How did Darwin come up with these important ideas? It all started when he went on a voyage. The Voyage of the Beagle In 1831, when Darwin was just 22 years old, he set sail on a scientific expedition on a ship called the HMS Beagle. He was the naturalist on the voyage. As a naturalist, it was his job to observe and collect specimens of plants, animals, rocks, and fossils wherever the expedition went ashore. The route the ship took and the stops they made are shown in the Figure below. Route of the voyage of the Beagle Voyage of the Beagle. This map shows the route of Darwin's 5-year voyage on the HMS Beagle. Each stop along the way is labeled. Darwin and the others on board eventually circled the globe.[Figure1] Darwin was fascinated by nature, so he loved his job on the Beagle. He spent more than 3 years of the 5-year trip exploring nature on distant continents and islands. While he was away, a former teacher published Darwin's accounts of his observations. By the time Darwin finally returned to England, he had become famous as a naturalist. Darwin's Observations During the long voyage, Darwin made many observations that helped him form his theory of evolution. For example: He visited tropical rainforests and other new habitats where he saw many plants and animals he had never seen before (see Figure below). This impressed him with the great diversity of life. He experienced an earthquake that lifted the ocean floor 2.7 meters (9 feet) above sea level. He also found rocks containing fossil sea shells in mountains high above sea level. These observations suggested that continents and oceans had changed dramatically over time and continue to change in dramatic ways. He visited rock ledges that had clearly once been beaches that had gradually built up over time. This suggested that slow, steady processes also change Earth's surface. He dug up fossils of gigantic extinct mammals, such as the ground sloth (see Figure below). This was hard evidence that organisms looked very different in the past. It suggested that living things—like Earth's surface—change over time. Animals in the Galapagos: giant marine iguana, blue-footed booby, giant ground sloth On his voyage, Darwin saw giant marine iguanas and blue-footed boobies. He also dug up the fossil skeleton of a giant ground sloth like the one shown here. From left: Giant Marine Iguana, Blue-Footed Boobies, and Fossil Skeleton of a Giant Ground Sloth[Figure2] The Galápagos Islands Darwin's most important observations were made on the Galápagos Islands (see map in Figure below). This is a group of 16 small volcanic islands 966 kilometers (600 miles) off the west coast of Ecuador, South America. Map of the Galapagos Galápagos Islands. This map shows the location of the Galápagos Islands that Darwin visited on his voyage.[Figure3] Individual Galápagos islands differ from one another in important ways. Some are rocky and dry. Others have better soil and more rainfall. Darwin noticed that the plants and animals on the different islands also differed. For example, the giant tortoises on one island had saddle-shaped shells, while those on another island had dome-shaped shells (see Figure below). People who lived on the islands could even tell the island a turtle came from by its shell. This started Darwin thinking about the origin of species. He wondered how each island came to have its own type of tortoise. Galapagos tortoises Galápagos Tortoises. Galápagos tortoises have differently shaped shells depending on which island they inhabit. Tortoises with saddle-shaped shells can reach up to eat plant leaves above their head. Tortoises with dome-shaped shells cannot reach up in this way. These two types of tortoises live on islands with different environments and food sources. How might this explain the differences in their shells?[Figure4] The Farallon Islands - "California's Galapagos" One of the most productive marine food webs on the planet is located on the Farallon Islands, just 28 miles off the San Francisco, California coast. These islands also host the largest seabird breeding colony in the continental United States, with over 300,000 breeding seabirds. The islands are known as the Galapagos of California. Why?

Inherited variation

Differences in physical traits of an individual from the group to which it belongs

Competition

Driving force of natural selection in which organisms fight for food, water, and living space.

Charles Darwin

Traveled to the Galapagos Islands on the HMS Beagle and later wrote the book "The Origin of Species." Largely credited with originating the theory of evolution.

Selective Advantage

When organisms possess an adaptational advantage that increases their likelihood of survival

allele frequency

proportion of one allele, compared with all the alleles for that trait, in the gene pool