L 2 Theories of Evolution Learning Objectives 1

L 2: Theories of Evolution Learning Objectives: 1. Describe Lamarck’s theory of evolution. 2. Describe Darwin’s theory of evolution. 3. Analyse the evidence for theories of evolution.

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.

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.

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.

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)

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).

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 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”.

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.