Evolution by natural selection How do species change over time?

Charles Darwin Born in England in 1809 Took a 5-year voyage on the HMS Beagle in 1831 Observed that species vary: –Globally –Locally –Over time

Evolution Based on his observations, Darwin developed the theory of biological evolution: –Explains how modern organisms evolved over LONG periods of time through descent from modern ancestors

Ideas that influenced Darwin Hutton –Geological change and “deep time” Lyell –Laws of nature are constant over time and scientists must explain past events in terms of processes they observe in the present Lamarck –Organisms could change during their lifetime by selectively using or not using parts of their body –Acquired traits could be passed on to offspring, leading to change in species over time

Lamarck’s Evolutionary Hypothesis

More Ideas that Influenced Darwin Malthus –Population growth of humans could lead to a lack of living space and food for some people –Provided a possible mechanism for Darwin’s ideas Artificial Selection –Nature provides variation –Humans select for those they find useful –Used in agriculture and with live stock

Evolution by Natural Selection Conditions under which natural selection could occur: –Struggle for existence: more individuals are born than can survive in the environment –Variation and adaptation: there is variation among individuals and some variations are more beneficial than others (adaptations) –Survival of the fittest: Differences in adaptations affect how well an organism can survive and reproduce (fitness)

Adaptations and Fitness Adaptations can involve body parts or behavior Adaptations that help an organism survive AND reproduce increase its fitness

How does evolution occur? Mechanism for evolution= natural selection Natural selection: process by which organisms with variations most suited to their local environment are more likely to survive and leave more offspring Over time, populations change as they become better adapted to their environment