Theories of Evolution

Jean Baptiste Lamarck (1744 – 1829) One of the first to propose a theory of evolution. Observed changes in the fossil record. He observed from that data that species changed over time. Believed that organisms could pass down acquired traits. Acquired traits – traits not determined by genes; traits gained by experience or behavior ie. Cheetahs exercised and increased leg strength, then passed that leg strengh on to their offspring. First to state that organisms change over time; newer organisms are modified versions of older organisms.

Teleology Derived from the root “telos” meaning end. Teleology – idea that evolution is purposeful or has a pre-determined result. Belief that everything happens for a reason. ie. Cheetahs were meant to become top predators, so they had to become faster to catch their prey.

Creationism/Intelligent Design Belief in a “creator” or “higher power”. Creationism Belief in the literal meaning of the Bible and other religious documents. Do not believe that species change significantly over time. Intelligent Design Belief that creator began the process of life. Recognize that species change over time, but do not believe that new species are created. ie. Cheetahs were created by God to be fast runners.

Charles Darwin He was hired as a naturalist for an expedition in 1831 on the H.M.S. Beagle. Read books on geology and noted that changes take place over millions of years, therefore, organisms must adapt to these changes. He collected specimens and recorded data from various locations (ie. Galapagos Islands). He noted differences between similar species living in different locations. Why were they different? Developed a theory called evolution by natural selection. This is now the most widely accepted evolutionary theory in scientific community.

Darwin’s Theory “Descent with Modification” – meaning that newer species are modified descendents of older species. Idea supported by Darwin’s observations Similar species showed different characteristics in different locations/islands. ie. Galapagos finches – compared birds on different islands Beaks shaped differently when different food sources present large, wide beak for cracking seeds. small, thin beak for catching insects.

Natural Selection Evolution by natural selection Proposed hypothesis for how evolution happens. Noticed that environmental factors (ie. food, territory, mates, predators) can limit the size of populations. Most populations do not grow unchecked. Two ways to limit population growth: increased death rate decreased reproduction rate

Natural Selection Main points of Darwin’s theory: All populations contain some variation. Not all individuals are the same within a group. Some organisms are more “fit” for their environment. Fitness – the ability of an organism to survive and reproduce in its environment. More fit organisms will have greater reproductive success. As a result, genes for these traits will be passed on more often. After time, the population as a whole may change. Adapt – to change genetically over time to become better suited for the environment ie. Cheetahs who were fast were more fit for the environment and more likely to survive and reproduce.

Important to Remember Evolution acts on populations, NOT individuals! Individuals do not change spontaneously. Changes may be seen in the population as a whole over millions of years. Evolution is NOT purposeful! Traits that are favorable in some environments may not be favorable in others. Change in the environment may cause change in populations.