The Basics

• The basics of Darwin's theory state that in a given population stronger or faster animals are more likely to survive (and thus pass on their genetic coding to their descendants). Over the course of millions of years, this causes successful species to evolve and grow stronger.
  
  

Natural Selection

• The heart of Darwin's theory lies in the notion of natural selection. It states that variation exists in any animal population, with individuals possessing different traits such as fur color, muscle structure, horn size and comparative intelligence. Those individuals that are better adapted to survive in their environment---say, a giraffe tall enough to eat from the tops of the trees, as opposed to one who can't reach that far---stand a better chance of thriving and thus passing on their traits to their offspring. Hence the term "survival of the fittest."
  
  

Species

• The same process of natural selection that applies to individual animals also applies to entire species. A species with numerous individuals well adapted to their environment will survive and prosper, while species which cannot adapt to their environment will perish.
  
  

Evolution

• Over time, this process of natural selection creates lasting changes in the species as a whole. Because the stronger, fitter and more agile animals have a better chance of surviving (and thus producing offspring with the same genetic traits), those traits eventually become dominant in the population. The process of improvement can eventually result in entirely new species, evolving from older ones that possessed less-advanced traits.
  
  

Creationism

• Darwin's theories engendered their share of controversy even in his time. Today, a number of religious groups question the validity of evolutionary theory and condemn its instruction in schools. They believe it stands in opposition to Biblical teachings, which state that God created the universe and all the creatures within it, and support an alternative theory known as creationism. Though widely discredited by scientists, creationism retains a number of adherents, and the ensuing controversy has kept Darwin's theories in the forefront of contemporary political debate.