Natural Selection

Darwin’s Voyages

Chapter 5

Section 1

A Darwin Voyage

• Evolution– A change over a

period of time

• Charles Darwin; 22– Voyage on the Beagle

• 1831– 5-year trip around the

world

– Started in England

Living Diversity

• Diversity– The variety of living

things on earth

• Scientists estimate…– Between 5-50 million

living species on earth right now

• Quite a guess!!!

Fossil Diversity

• Fossils give us a glimpse into the past

• Extinction– 99.9% of all species

that have ever lived are now extinct

Adaptations

• Physical and behavioral traits– Enable organisms to

survive• Catch food• Withstand conditions• Reproduce

Fitness

• The ability of an individual to survive & reproduce

• To successfully pass on its genes to its offspring

The Galapagos Islands

• 1000 kilometers west of S. America – 600 miles

• Small & short islands– Dry & hot

• Larger & taller islands– More lush

Darwin’s Finches

• 1 species of finch evolved into many different “specialized” species

Giant Tortoise Shells

• Tortoises from different islands had different shells

• Ah, hah!!!!– Natural Selection

• Survival of the fittest– Evolution!!!

Vestigial Organs

• Wings on flightless birds

• Tailbones on primates

Homologous Structures

• Develop from similar tissues in the early development stages of the organism

Arguments for an Ancient Earth

• River Valleys– Carved by glaciers over 100,000’s years

• Shells found in high elevation mountains– Plate tectonics!!!

Problems with Reproduction

• Extinction– Birth Rate < Death Rate

• Over Population– Birth Rate > Death Rate

• Disease• Famine• War

Peppered Moths

• Before the industrial revolution, England– Trees were light in

color from lichen growing on them

• After the pollution from Ind. Rev.– Lichen died, leaving

just the dark bark

Helpful Mutations

• Increases fitness– more offspring than others in population

• Becomes more common in the population

Evolution

• Any change to the relative frequencies of alleles in the gene pool of a species

Species

• A group of similar-looking organisms that can breed with one another and produce fertile offspring– Bobcat & Lynx

Natural Selection

• The struggle for existence selects only the fittest individuals to survive in nature– Generation after generation

Struggle for Existence

• Only the fastest rabbits will escape the lynx

• Only the fastest lynx will catch the rabbits