Unit B

Module 4 ~ Lesson 2

 Hypotheses, Theories, and Laws

Scientific knowledge is accumulated, organized, and used to develop hypotheses and theories.  Hypotheses  are tested over time and are accepted or rejected. When a hypothesis consistently predicts and correctly explains observations, a scientific theory will eventually develop.


Watch this video for an explanation of scientific laws and theories.

 Developing the Theory of Evolution by Natural Selection

For many years, most scientists and philosophers agreed that life forms were unchanging. Comte de Buffon was the first to challenge this view in 1749, suggesting that humans and apes may share an ancestor. By the early 1800s, other scientists began to share Buffon's ideas. 

Georges Cuvier was a naturalist who developed the science of  paleontology . He studied  fossils  and made predictions about life in the past. He proposed the idea that Earth had experienced many destructive natural events, such as floods and volcanic eruptions. Cuvier proposed that these events were violent enough to have eliminated many species.

Image by Adolfo Beato from Pixabay

Charles Lyell rejected Cuvier's proposal and suggested that geological processes were slow and that the Earth may be much older than the 6,000 years most people believed it to be.

Jean-Baptiste Lamarck compared fossils to current species of animals and proposed that species changed over time. Lamarck noticed the changing form of species and provided a hypothesis for this change. Lamarck believed that offspring inherited the beneficial  acquired characteristics  of their parents. At the time, even Darwin conscripted to this theory.
Darwin travelled from England to South America to Australia and back to South America during his  five-year  voyage aboard the HMS Beagle. Observations he made in England and while exploring caused Darwin to ask many questions about the natural world and eventually develop the theory of evolution by natural selection.

Nathan Hughes Hamilton. (2018). Map of Cook and Darwin Voyages. CC-BY via Flickr


Read "Developing a Theory to Explain Change" and "Developing the Theory of Evolution by Natural Selection" on pages 122 to 124 of your textbook.

Read "Table 4.1 Darwin's Observations and Questions Arising from Them" on page 125 of your textbook.


Cuvier would have suggested the species of fish had become extinct, possibly due to a natural catastrophe, such as a flood or a volcanic eruption.
Lyell rejected the idea of catastrophism and guessed that Earth changed slowly and continuously over time. His idea also suggested that Earth was older than 6,000 years. He believed that slow, continuous change would amount to large changes over time. This influenced other thinkers, such as Charles Darwin, who wondered if the same sort of processes and timelines were also occurring in populations.