Study GuidePlant Biology–Evolution1.Darwin's Theory of Evolution1.1What Is Evolution?Evolution is how living populations change over long periods of time. These changes happen asorganisms respond to their environment. The instructions for these changes are stored in DNA andpassed from parents to offspring. Over millions of years, this process has led from very simple lifeforms to the wide variety of complex organisms we see today.The idea of evolution is closely connected toCharles Darwinand his explanation ofnaturalselection. When combined with modern genetics, Darwin’s ideas form the foundation of today’stheory of evolution.1.2Darwin’s Big Ideas About LifeIn his bookOn the Origin of Species, Darwin explained how life changes over time. When we simplifyhis ideas and include what scientists know today, his main points are:•All living things likely came from one or a few very simple organisms.•New species do not appear suddenly. They slowly develop from existing species.•Organisms compete with each other for limited resources.•Those that are less well adapted to their environment are more likely to die out (extinction).•The fossil record has gaps, which explains why we do not always see clear transitional forms.These ideas set the stage for understandingwhyevolution happens.1.3Why Does Evolution Occur?Darwin noticed several important patterns in nature:•Organisms produce more offspring than can survive.•Populations usually stay about the same size because food, space, and other resources arelimited.Preview Mode
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