Ideas that shaped Darwin’s thinking Section 16.2

Geological breakthroughs During Darwin’s time, humanity's understanding of the Earth was changing rapidly James Hutton and Charles Lyell famously suggested that the Earth of extremely old, and that processes that occurred in the past are the same processes that operate in the present Uniformitarianism Hutton presented his work in 1785 Lyell published his first great work – principles of geology in 1830

James Hutton – Age of the Earth Hutton made a number of observations of the Earth He linked together a number of geological process Cooling magma to make igneous rocks Uplift to make mountains Erosion to reduce mountains and make sedimentary rocks All of these processes take a very long time Introduce the concept of deep time, and that the Earth must be more than a few thousand years old

Charles Lyell – Uniformitarianism Lyell argues that laws of nature are constant, and that scientists must be able to explain past events in terms of processes that occur in the present Concept of uniformitarianism - the present is the key to the past Volcanoes released lava and gas in the past the same way they do today Rivers erode canyons the same way they do today The Earth needs to be old enough to be able to form the numerous structures and phenomena that we can see across it’s surface Darwin read Lyell’s book, and it influenced his understanding of the world Darwin asked if the Earth can change over long periods of time, can animals?

Did anyone come up with the idea of evolution before Darwin? Yes! Throughout the 19th Century, the fossil record gave the idea that life had somehow evolved A Frenchman – John Baptiste Lamarck proposed that organisms could change during their lifetimes, by selectively using or not using parts of their bodies Acquired traits could be passed on to offspring, enabling species to change over time Published in 1809 - the year Darwin was born

What does this mean? Lamarck suggested that all organisms have an inbuilt drive to become more complex and perfect Organisms will change and acquire features that make them live more successfully in their environment Example – water bird could develop long legs as it began to wade in deeper water looking for bird The body could adapt to it’s new surroundings Traits altered by an organism were called acquired characteristics He proposed that if a bird acquired a new trait, such as longer legs it could pass it on to it’s offspring

Why were Lamarck's ideas incorrect? Organisms don’t automatically want to become perfect Evolution does not mean that organisms want o become better, nor does it happen in a predetermined direction Traits acquired by individuals can not be passed on to offspring But, he did recognize that species are not fixed He tried to explain evolution using natural processes He recognized a link between environment and body structures His work paved the way for people like Darwin

Thomas Malthus In 1798, Thomas Malthus recognized that humans were being born faster than they were dying This resulted in overcrowding He proposed that if population growth continued unchecked there would not be enough space for everyone War, famine and disease were three factors that control population growth Darwin took Malthus’s work and applied it to nature In nature, most offspring die before they reach maturity, and only a few manage to reproduce Darwin used this theory to investigate why certain individuals in a population survive, and look to see if there was any pattern

Artificial selection Darwin investigated changes produced by plant and animal breeders Breeders know that individual organisms vary, and it is possible to pass on these traits to offspring Used to improve crops and livestock The process of farmers breeding specific animals or plants for certain characteristics is called artificial selection Nature provides the variation, and humans use what is useful Darwin tested the idea of artificial selection by breeding fancy pigeons

Why is this important? At first Darwin didn’t recognize the importance of variations within a species Thought to be minor defects Darwin recognized that these minor defects provided the possibility for evolution This is the basis for his theory of evolution

Assignment Discuss with you neighbor the key people who influenced Darwin and his theory of evolution Create a timeline in your notes displaying this key bits of information Use the textbook to help you Add as much detail as possible Current understanding in the world at each time period What each scientist did How their contributions helped to change the general understanding of the world Basic example to help you on page 459 – but go into more detail!