Section 5.4 The Making of a Theory Chapter 5 Section 5.4 The Making of a Theory

Lamarck’s Theory In the early 1800’s, Lamarck proposed the first theory of evolution. Lamarck believed that new, very simple species were continually being created by spontaneous generation. Spontaneous generation is the formation of life from non-living matter.

He believed that organisms had a “force” or “desire” to change for the better and that they were able to simply produce new parts (acquired traits) to become better adapted to their environment. He reasoned that these acquired traits could be passed on to the offspring and over generations lead to the eventual permanency of them within the species. He called this theory inheritance of acquired characteristics.

Problems with Lamarck’s Theory Acquired traits are features that we gain over a life-time. Examples of acquired traits are flexibility, fitness, length of hair. These are things that cannot be passed on or inherited by the next generation.

Darwin’s Theory In 1831, Charles Darwin embarked on a journey to travel the world and gather scientific evidence. He came up with the following evidence. 1. In South America, he observed unusual fossil species that resembled giant sloths and armadillos. He suspected that the living forms might be descended from the fossilized species.

2. He noted that species living in South American tropics did not resemble those living in the African tropics. He inferred that each landmass might have acted like an isolated nursery, where the species evolved independently. 3. The Galapagos Islands was home to 13 very similar species of finches. Each with individual characteristics that helped them in their specific environment.

4. He became convinced that geological forces, such as earthquakes could account for the location of fossils and mountains.

Long after his voyage he began looking at artificial selection and the fact that certain traits can be inherited by the next generation. Then he looked at a piece of information that said animals usually produce more offspring than survive. From this evidence he suggested that there must be competition for survival and he looked at why some survive over others.

From all of his evidence he put together a workable theory of evolution by natural selection. Natural Selection – the idea that evolution occurs because those individuals best suited for survival are more likely to reproduce and pass their traits to the next generation.

The Theory of Evolution by Natural Selection Observation 1 Individuals within any species exhibit many inherited characteristics. Observation 2 Every generation produces far more offspring than can survive to reproduce. Observation 3 Populations of species tend to remain stable over time. Inference 1 Individuals of the same species are in a constant struggle for survival Inference 2 Individuals with more favourable variations are more likely to survive and pass those variations on. Inference 3 Since individuals with more favourable conditions contribute more offspring to the next generation, their characteristics will become more common.