The Theory of Evolution

Old Theories of EvolutionJean Baptiste Lamarck

(early 1800’s) proposed:“The inheritance of

acquired characteristics”

He proposed that by using or not using its body parts, an individual tends to develop certain characteristics, which it passes on to its offspring.

“The Inheritance of Acquired Characteristics”Example:

A giraffe acquired its long neck because its ancestor stretched higher and higher into the trees to reach leaves, and that the animal’s increasingly lengthened neck was passed on to its offspring.

Popular Belief (Before Darwin)Species were

created at the same time and remained unchanged

Features may be passed on to allow survival of a species

Darwin’s Theory of EvolutionEvolution, or change over time, is the

process by which modern organisms have descended from ancient organisms.

A scientific theory is a well-supported testable explanation of phenomena that have occurred in the natural world.

History of Darwin’s StudiesDarwin went on an

around-the-world trip on the HMS Beagle and traveled to the Galapagos Islands.

He particularly liked and observed the finches. He also observed the tortoises on different islands.

He observed each different group had its own niche.

He studied 13 different species and saw how they adapted to their environment.

Diversity in Finches

The Galapagos IslandsThe smallest, lowest islands were

hot, dry, and nearly barren sparse vegetation.

The higher islands had greater rainfall and a different assortment of plants and animals had rich vegetation.

The Galapagos Island TortoisesGiant tortoises

varied in predictable ways from one island to another.

The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited.

Charles Darwin - The AuthorWrote in 1859:“On the Origin of Species by Means of Natural Selection”

Natural SelectionNatural Selection leads to organisms that

are well suited in particular environments.Individuals with favorable traits are more

likely to leave more offspring better suited for their environment

It provides a scientific explanation for the history of life on Earth as depicted in the fossil record and similarities evident within the diversity of existing organisms.

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5 Main Points1. There is variation with a

population.2. Some variations are

favorable.3. Not all young produced in

each generation survive.4. Individuals that survive

and reproduce are those with favorable variations.

5. Descent with Modification

Ostriches are the fasted birds on land due to favorable traits such as long, powerful legs.1.31

Evolution by Natural SelectionThe Struggle for Existence-

members of each species have to compete for food, shelter, other life necessities

Survival of the Fittest-Individuals that are best suited to an environment (adaptations that enable fitness) survive and reproduce most successfully.

SummaryEach organism is unique, each has

advantages and disadvantages in the struggle for existence

Species alive today descended with modification from species that lived in the past

All organisms on earth are united into a single family tree of life by common descent