© Boardworks Ltd 20091 of 7. © Boardworks Ltd 20092 of 7 The first well- known theory of...


The first well-known theory of

evolution:


The short-necked ancestors of modern giraffes needed to reach the leaves on tall trees when food was scarce.

Lamarck’s theory of evolution:The Theory of Use/Disuse and Acquired Traits

How would this theory explain a giraffe’s long neck?

Over their lifetimes these giraffes stretched their necks; a trait which was then passed on to their offspring.

Jean-Baptiste Lamarck (1744-1829) was a French botanist who believed that species evolved because they inherited traits acquired through the over or under-use of body parts.


The Inheritance of Acquired Traits

• Lamarck believed that acquired traits could be inherited (ex. If you stretched your neck, dyed your hair, lost an arm, or had a large scar on your foot, your offspring will have those traits.)

• He also believed that all species had a tendency toward perfection – that species were becoming more perfect with each generation.


Was Lamarck right???

NO


Darwin’s theory of evolution by natural selection

The British naturalist Charles Darwin (1809–1882) later suggested a more persuasive argument for evolution.

Darwin proposed that evolution took place through natural selection.

Darwin developed his theory of evolution after noticing close similarities between certain fossils and the adaptations of modern day animals he saw during his round-the-world voyage on the HMS Beagle.


Who was Charles Darwin?


He also used his own experience…

• Darwin bred pigeons. • He noticed that he could breed pigeons to

have certain traits (i.e., purple wings, a large wingspan, a certain song.)

• He called this artificial selection: when humans breed organisms to get specific traits in offspring.

• If HE could select traits in offspring of pigeons, maybe something in nature is doing this as well…


Due to natural variation, the ancestors of modern giraffes would have had necks of different length.

How does Darwin’s theory explain a giraffe’s long neck?

How the giraffe got its neck

As a result, the long-necked giraffes were more likely to be healthy and live to produce more high-quality offspring.

This, in turn, would increase the chances of their long-necked characteristic (an adaptation for the environment) being passed on to future generations.

Giraffes with longer necks would have been able to reach more food than those with shorter necks.


Natural selection


Do organisms choose to adapt?

• NO!• Because of natural variations, some are just

more fit than others.• The traits that made organisms more fit he called

adaptations for the environment.• Fitness: ability to survive and reproduce in a

certain environment.• “Survival of the fittest” refers to the fact that

the organisms with the best adaptations (the most fit) will survive and reproduce better than the less fit organisms.


Galápagos finches

Darwin thought all the finches could have evolved from one type of finch that came from the mainland.

Some finches had strong and claw-like beaks, suitable for crushing seeds. They were more fit in environments with seeds.

Other finches had thin and delicate beaks, suitable for picking insects from holes in the ground. They were more adapted to islands with many insects.

In the Galápagos, Darwin noticed that different islands had different types of finches, with variations in their beaks.

Natural variation meant that some finches had slightly different beaks. These finches would have been able to eat different types of food and avoid competition. They wouldtherefore have survived and passed on their genes.


Adaptive radiation (one species adapting to many different environments)


Darwin’s 4 parts of natural selection:

• 1) Variation exists within species• 2) Organisms compete for natural

resources• 3) Organisms produce more offspring than

what can survive• 4) Environment selects organisms with

beneficial trait:AKA- “ Natural Selection” – Survival of the fittest

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