Chapter 15 - Evolution

Chapter 15 - Evolution Section 15 -1

What is Evolution?? • “Evolution is ...the sequence of events involved in the evolutionary development of a species or group of organisms . In the "big picture" evolution is the process of change which LIFE has under gone since its origin. • Evolution is change over time….

The Theory of Natural Selection • What is a theory? • Watch the video: Evolution Primer #1: Isn't Evolution Just a Theory?

The Theory of Natural Selection • Charles Darwin (18091882) - Proposed the Theory of Natural Selection. Naturalist on the Voyage of H.M.S. Beagle (1831-1836) Set sail 2 days after Christmas 1831. • Watch the video: Evolution Primer #2: Who Was Charles Darwin?

Darwin’s 5 year Voyage on the HMS Beagle

The Galápagos Islands • The Galápagos Islands have species found in no other part of the world, though similar ones exist on the west coast of South America. Darwin was struck by the fact that the birds were slightly different from one island to another. He realized that the key to why this difference existed was connected with the fact that the various species live in different kinds of environments.

Darwin identified 13 species of finches in the Galápagos Islands. This was puzzling since he knew of only one species of this bird on the mainland of South America, nearly 600 miles to the east, where they had all presumably originated.

• He observed that the Galápagos species differed from each other in beak size and shape. He also noted that the beak varieties were associated with diets based on different foods. He concluded that when the original South American finches reached the islands, they dispersed to different environments where they had to adapt to different conditions. Over many generations, they changed anatomically in ways that allowed them to get enough food and survive to reproduce.

Artificial Selection • So evolution is just change over time – the organism will change and adapt for survival over generations. • Darwin inferred that we could speed up evolution to suit our own needs by choosing those traits in plants and animals that we wanted to select

Artificial Selection in Pets

Artificial Selection • As shown here, farmers have cultivated numerous popular crops from the wild mustard, by artificially selecting for certain attributes.

Artificial Selection in Cattle • “Since our entry in the Texas Longhorn business in 1984, we have used selection, artificial insemination, and embryo transfer to accomplish a small but quality herd. “ • I found this quote and picture on a website – it illustrates artificial selection in cattle breeding.

Natural Selection • Natural Selection • Natural selection is the process of interaction between an organism and its environment that results in the differential rate of reproduction of different phenotypes in the population. • Natural Selection is the most important agent of evolution. • Selection acts on phenotypes. • The result of natural selection is a a change in the allele frequencies in a population.

Influence of Thomas Malthus • One of Darwin’s influences was Thomas Robert Malthus, a late-eighteenth century economist. Malthus wrote "Essay on the Principle of Population" (1798), which Darwin read and was inspired by. The central theme of Malthus' work was that population growth would always overpower food supply growth, creating perpetual states of hunger, disease, and struggle. The natural, ever-present struggle for survival caught the attention of Darwin, and he extended Malthus' principle to the evolutionary scheme.

Influence of Thomas Malthus • Darwin considered that some of the competitors in Malthus' perpetual struggle would be better equipped to survive. Those that were less able would die out, leaving only those with the more desirable traits

Variation • For many traits that occur in a population, individuals are often not all identical. For example, if running speed were measured, some individuals would likely be able to run faster than others but most individuals would probably be intermediate.

Heritability • Traits Are Heritable • Those individuals that survive better or reproduce more will pass their superior genes to the next generation. Individuals that do not survive well or that reproduce less as a result of "poorer genes" will not pass those genes to the next generation in high numbers. As a result, the population will change from one generation to the next. The frequency of individuals with better genes will increase.

Overproduction •

Overproduction means more offspring of a species are produced than can possibly all survive. The ones that have characteristics that make them better at feeding, hiding, getting mates etc. tend to be the ones that survive and pass on their genes to the next generation. This means that, of the great diversity in the babies born in a generation, specific traits tend to make them successful and these traits get passed on more effectively and so a higher % of the next generation have these "adaptive' traits.

Reproductive Advantage • Some variations confer a reproductive advantage to the organism in certain environments. In the case of the trees, those which grow taller may receive more light than those that are shorter, and so the taller trees have more energy to spend producing seeds.

• End of Section 15.1 • Assessment questions • 1. Darwin collected specimens and fossils in the Galapagos, in South America, and in other locations – he was able to formulate his theory by making observations on the linkages he found

2. • Darwin observed variation in individuals and realized that variation was heritable . He realized that selection (artificial) could lead to changes over time and that this concept should also apply to natural selection.

3. • A. more offspring of a species are produced than can possibly all surviveexample: mice have many more babies than can survive

3. • B. Individuals in a population have variation – example in a herd of horses the horses will not all look the same

3. • C. Variations can be inherited - example Variation in a human characteristic, as a result of inheritance from the parents, is called inherited variation. Here are some examples:

• eye colour • hair colour • skin colour

3. • D. Variations increasing reproductive success will be more common in the next generation – example more colourful plumage on male birds makes them more successful at attracting females

4. • Wallace came to the same conclusion as Darwin I think you are right about Natural Selection. Charles

Thank you Alfred