Where do we all come from? And why are we all so different? evolution This used to be a questioned posed and answered only by philosophers, not scientists. Where do we all come from? And why are we all so different?

Diversity? How does variation happen?

Fixity of Species Ancient scholars (e.g. Aristotle (384-322 B.C.), Biblical philosophers and most ordinary people used to believe in the “fixity of species". All species had come into existence at the same time (i.e. at the time of creation), and hadn't changed since then. This thinking survived up until the 1800's. At about that time, the idea that species could change was beginning to be accepted by scientists. The process by which modern organisms have evolved from ancient organisms is called evolution. How this occurred was not understood yet.

Jean Baptiste Lamark proposed a theory of evolution based on ACQUIRED CHARACTERISTICS which correlated to three assumptions: Law of use and disuse Law of inheritance of acquired traits A desire to change

Theory of Acquired Characteristics If a GIRAFFE stretched its neck for leaves a "nervous fluid" would flow into its neck and make it longer. Its offspring would inherit the longer neck, and continued stretching would make it longer still over several generations. Meanwhile organs that organisms stopped using would shrink. Lamarck believed that the long necks of giraffes evolved as generations of giraffes reached forever higher leaves.

Lamarck was wrong! In reality, body structures changed by environmental influences do not alter the genes of that animal, which are all that can be passed on to the next generation. Although later discoveries did not support Lamarck’s theory; he is credited with brining up the concept of evolution. His ideas paved the way for the ideas of Charles Darwin.

Theory of Natural Selection In the mid-1800s, British naturalist CHARLES DARWIN and the English biologist ALFRED RUSSEL WALLACE independently thought of a way for life to change – a process Darwin called NATURAL SELECTION. Natural selection is now considered one of the BASIC MECHANISMS of evolution - along with mutation, genetic drift, gene flow and non-random mating.

Fitness and Adaptation Darwin also noted that most organisms have physical traits and behaviors that allow them to survive and reproduce in their environment. Darwin called this fitness and argued that fitness arises through a process called adaptation. Successful adaptations allow organisms to be better suited to their environment therefore better able to survive and reproduce. Quills are an adaptation that almost completely eliminates the risk of predation for porcupines

Idea’s that shaped Charles’ Darwin’s Theory of Evolution In 1831, Darwin left for a 5 year trip around the world aboard the HMS Beagle as the ship's naturalist. Observed many different animals, and fossils of extinct creatures. Visited the Galapagos Islands off S. America where he did most of his work. Observed variations in tortoises and finches. Believed the earth was much older than most people thought based on Charles Lyell’s book Principals of Geology and the work done by James Hutton. The influence of farmers and artificial selection. In artificial selection, the intervention of humans ensures that only individuals with the more desirable traits produce offspring.

Decided that species did change with time, but not in the way that Lamarck has suggested. Came home and wrote a paper on the topic, but did not release until receiving a letter from Alfred Russel Wallace who had independently come to the same conclusion. Both had been inspired for part of their ideas by Thomas Malthus' 1838 paper "An Essay on Population", which stated that populations increase faster than food supply. Darwin and Wallace jointly announced their theory and Darwin published On the Origin of Species by Means of Natural Selection in 1859. The world has never been the same!

Darwin and Common Descent Darwin’s book changed the way people think about the living world. In the book Darwin maintained that modern organisms have been produced through evolution. That each new organism comes from preexisting organisms; that each species has descended from other species. And if you look back far enough you will see that all species have shared a common ancestor. Darwin called this principle common descent.

The Darwin-Wallace theory of evolution can be summed up as follows Populations will increase at a geometric rate. (e.g. a single oyster may pass as many as 114,000,000 eggs at a single spawning). However, populations are basically constant. If 1 and 2 above are true, there must be a struggle for existence. There is variation within each species. Some traits are more favourable for survival than others. Favourable traits are passed on to offspring. Thus, after many generations, most of the members of the population have the selected trait.

Evolution can be defined as: the process by which related populations diverge from one another, giving rise to new species.