Charles Darwin & Natural Selection

Darwin

▧ Born in Shrewsbury, England, in 1809▧ Studied medicine at Edinburgh University

(1825-1827) where the sight of blood and surgery without anesthetics repulsed him

▧ Studied to become a clergyman at Cambridge University (1827-1831)

The Beagle

▧ After Cambridge, Charles was recommended for a surveying trip on the HMS Beagle

▧ He sailed aboard the Beagle for 5 years, working as a naturalist.

▧ On his voyage, he made many observations and collected evidence to help form his theory about the way life changes (EVOLUTION)

The Beagle

▧ The Beagle sailed around the world from 1831-1836.

▧ At the time Darwin made his trip, the majority of people believed the Earth and all of its forms of life had been created only a few thousand years in the past.

▧ People also believed that the Earth had not changed during those few thousand years.

▧ People also believed in the fixity of species; that species never changed.

The Beagle

▧ After careful observation and study of new scientific discoveries, Darwin began to think otherwise.

The first dinosaur to be described scientifically was Megalosaurus by William Buckland in 1824.

The Father of Geology▧ Darwin was influenced by

geologist James Hutton’s writings that described geologic forces that he thought had changed and were still changing the Earth

▧ Hutton proposed that the Earth had to be much more than a few thousand years old.

Charles Lyell▧ Darwin was also influenced

by geologist Charles Lyell who wrote Principia Geologica

▧ Lyell’s book proposed that tremendous geologic processes had shaped the Earth such as seen in volcanoes active in the present

Back to the Beagle▧ On the voyage,

Darwin noticed that everywhere he went, the animals and plants differed vastly.

▧ Patterns in the species suggested that the species had changed over time and had given rise to new and different species.

Galapagos Islands▧ Many of Darwin’s conclusions were based on

observations of wildlife in the Galapagos Islands.

▧ The Galapagos Islands lie 500 miles west of Ecuador in the Pacific Ocean, directly on the equator.

▧ “Galapagos” means turtle.

The Finches▧ Darwin noticed that there were several types

of finches on these islands. ▧ In particular, he

noticed that all the finches looked like a bird he had seen on the South American continent.

The Finches▧ He wondered if the birds and other animals

had been created to match their environment, why didn’t these birds look like the birds of the African continent, since the environments of both the Galapagos and Africa were similar.

▧ Darwin guessed that some of the birds from South America migrated to the Galapagos.

▧ Once on the islands, the birds must have changed over the years.

The Finches▧ This would explain the numerous species of

birds present.

Cactus finch

Large ground finch

Woodpecker finch

Descent with Modifications

Darwin concluded that each species had descended, with changes, from other

species over time.

EvolutionChange in a species over time

Thomas Malthus▧ Darwin based his theory on

his own observations and the writings of Thomas Malthus.

▧ Malthus was a British social scientist who made observations about population control in humans: ○ People have more children

than are able to survive. ○ There are built in

population checks: disease, famine, and war.

Darwin extended these principles to biology and proposed a mechanism for evolution called

Survival of the Fittest

Natural Selectionor

Natural SelectionFive basic components

1. Genetic Variation▧ All species have genetic variation▧ Every species is different, even within itself

(Look around! All of us are different)

2. Organisms produce more offspring than can survive

▧ Many that do survive do not reproduce. ▧ The female green sea turtle lays a clutch of

about 110 eggs. She may lay several clutches. It is likely that less than 1% will ever reach sexual maturity.

3. Since more organisms are produced than can survive,

there is competition▧ Competition is struggle for existence ▧ Competition exists WITHIN and AMONG

species

Both: food, water,

shelter, space

Within a species: mates

Among species

The Struggle▧ The constant struggle for survival is

affected by short term natural disasters and long term environmental changes

Short Term● Drought● Fires● Floods● Snowstorms● Hurricanes● Tornadoes

Long Term● Ice ages● Biome shifts

4. Survival of the Fittest ▧ Some organisms are more suited to their

environment as a result of variations in the species

▧ Fitness: the ability of an individual to survive and reproduce in its specific environment. Fitness is a result of adaptations.

▧ Individuals that are fit to their environment survive and leave more offspring than those who aren’t.

▧ He who spreads the most genes wins!

5. Descent with Modification▧ Living species today are descended with

modifications from common ancestral species that lived in the past.

▧ Characteristics of fit individuals increase in a population over time.

▧ Over time, genes for less favored characteristics will be eliminated from the gene pool ○ ex: giraffes and their increasingly longer necks.

Natural Selection: Survival of the Fittest

▧ Adaptation: any inherited characteristic (genetic variation) that can increase an organism’s chance of survival.

▧ An organism does not change because of need or desire to survive. The organism either already has the variation that enables it to survive or it dies.

The variation

exists

The environment

changes

A variation may give an advantage to

survive environmental

change

Types of Selection1. Directional selection: when natural selection

favors one extreme of continuous variation ➔ Example: Darker peppered moths can blend

in with the dark trees, allowing them to survive and reproduce

Types of Selection2. Disruptive selection: when natural selection

favors both extremes of continuous variation ➔ Results in formation of two distinct groups ➔ Example: Lighter colored oysters blend in

with the sand and darker ones blend into the shadows; medium colored ones are easy targets

Types of Selection3. Stabilizing selection: when natural selection

favors the intermediate states of continuous variation

➔ Example: Birds who lay too many eggs can’t provide for them all, so the offspring starve; birds who lay too few eggs don’t have enough offspring survive

Extinction▧ As the environment

changes, organisms must have variations that allow them to survive (adapt) to those changes or die

▧ If an entire population of a species cannot adapt, that species becomes extinct or dies out.

Mass Extinction▧ There have been

at least 5 MASS extinctions during Earth’s history where a huge percentage of the living species were destroyed.

▧ At least one of these has been attributed to meteor impact and it’s consequences.

Mass Extinction▧ Many scientists

say that the earth is currently experiencing a mass extinction crisis.

It’s estimated that ⅕ of more of the world’s species will become extinct if the rainforests are destroyed.

Mass Extinction▧ If we are in a period of mass extinction,

what animals will your grandchildren be able to see in the wild?

▧ Visit the World Wildlife Fund website for more information on endangered species.

Works Cited▧ Davis, Donald E. “Meteor Impact”. (Also public domain from NASA.) No

date. Online image with permission. Dinosaurs and Their Extinction. June 10, 2004. <http://www.donaldedavis.com/PARTS/DDDINOS.html>

▧ “Snow Alaska”. No date. Online image. Public Domain. Mineral Management Service. June 10, 2004. GeekPhilospher.com <http://geekphilosopher.com/bkg/snowAlaskaIce.htm>

▧ “Clearcut in Cameroon Rainforest”. No date. Online image. June 11, 2004. Earth Crash Earth Spirit. <http://www.eces.org/archive/gallery/forestsgfx/forests39.shtml>

▧ Harvey, Martin. No date. Online image. World Wildlife Fund. June 11, 2004. <http://www.panda.org>

▧ “Allosaur”. No date. Online image. Public Domain. Dinosaur National Monument. National Park Service. June 10, 2004. http://www.nps.gov/dino/index.htm