1. L2: Theories of Evolution
Learning Objectives:
Describe Lamarck’s theory of evolution.
Describe Darwin’s theory of evolution.
Analyse the evidence for theories of evolution.

2. Lamarck’s Theory of Evolution
Jean Baptiste Lamarck – French biologist in the late 1700’s
Lamarck’s theory
“Fountain of life”, all creatures were originally descended from worms.
Organisms evolved by adapting to their environments.
The change in species was caused by inheritance of acquired characteristics.

3. Lamarck’s Theory – Use it or Lose it
Lamarck believed that acquired traits (such as bigger muscles from increased use) caused organisms to better adapt to their environment.
He believed that these traits were passed from parent to offspring.
These changes accumulated over time.
If a feature was not used, it would shrink and be lost.

4. Example: Giraffe
Lamarck believed that the giraffe stretched it’s neck from trying to reach taller trees.
Over it’s life the neck grew longer from this.
This slightly longer neck was then passed on to children.
Over many generations the length of the neck steadily increased due to the stretching action of each generation.

5. Problems with Lamarck’s Theory
No evidence for the “fountain of life”.
Evidence that acquired traits (changes in the body) were not passed on to children. (Example: weightlifter builds lots of muscle, children are not born with lots of muscle because of this)

6. Darwin’s Theory of Evolution
Charles Darwin – English naturalist and geologist of the early 1800’s
Darwin’s Theory of Evolution
All organisms descended from a common ancestor.
Species evolved through the process of natural selection (survival of the fittest).

7. Evidence for Darwin’s theory
Evidence of similar species adapting differently on different islands of the Galapagos Islands (Galapagos Finches adapt different beaks).
Selective breeding experiments with pigeons proved that artificial selection can cause changes in a population.
He collected evidence from other scientists as well and published his famous book “On the Origin of Species by means of Natural Selection”.

8. Controversy
The scientific community today agree with Darwin’s theory of evolution by natural selection.
However, when the book was first published it was not accepted.
Why?
It challenged religious beliefs.
Scientists thought there wasn’t enough evidence. (Fossil evidence later found)
No way to explain variety and inheritance as DNA and genes had not yet been discovered.