Evidence of Evolution

Picture of Charles Darwin
Click on image for full size
The Bettmann Archive

The Theory of Natural Selection

During the 19th century when Europeans were exploring their own countries as well as mounting large expeditions to explore foreign lands, natural historians such as Charles Darwin and Alfred Russel Wallace were making observations of the geographic distributions of species. They found that different species were found in different environments. Species in the tropics were well suited, or adapted, to live in the tropics and species in England were well adapted to live in England. Finches on different Galapagos Islands were well adapted to their particular environments. Independent of one another, Darwin and Wallace both developed the theory of natural selection to explain the geographic distributions of species. That theory states that there are variations in organisms of the same species. Some are tall, some are short, some have larger mouths, keen eyesight, etc. The organisms that are most well suited to live in a particular environment are more likely to survive. The survivors produce the next generation and those offspring are more likely to have their parent's special traits (such as keen eyesight, etc.)

Here are the main points of the theory of natural selection:

  1. Everyone’s Different: There are variations among individuals of the same species (better eyesight, extra feathers, longer legs, etc.)
  2. Resources are Limited: Resources such as food and shelter are limited
  3. Lots of Babies: Organisms make more babies (young) than could actually live in the environment.
  4. Organisms Compete: Organisms compete for food and other resources in the environment.
  5. The "Fittest" Survive: The organisms whose variations best fit the environment are most likely to survive, reproduce, and pass useful traits to the next generation.

The evidence of evolutionary changes in life forms through time has been well established and accepted for more than a century. Natural selection is an explanation for the mechanism of evolution. In addition, scientists continue to investigate more specific hypotheses that might further develop our understanding of how change through time happens. One of the main hypotheses, developed by Stephen J. Gould and Niles Eldridge, is called punctuated equilibrium. This hypothesis suggests that the rate of change in a population is not constant. No changes, or very few, may happen to a population of organisms over millions of years and then changes may happen rapidly over many thousands of years. Advances in technology over the past century have allowed scientists to continue to test hypotheses that further our understanding of evolutionary processes.

Last modified May 16, 2005 by Lisa Gardiner.

You might also be interested in:

Cool It! Game

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Evolution Impacts Environment, Study Finds

Ecosystems have an impact on how living things evolve. And evolution has an impact on ecosystems too. Scientists have discovered the evolution of small fish called guppies affects the streams in which...more

Radiation is Dangerous to Living Creatures

Radiation can be harmful to living creatures. Radiation can harm living things directly by damaging their cells. The cells might stop functioning, or they might be unable to reproduce. Radiation can also...more

ExploraTour - Looking at the World in a Different Light

Look at the bed below the body of the sleeping man. You can still see where he was lying down. The heat from his body warmed up the bed sheets which are now radiating infrared light toward your eyes....more

ExploraTour - Looking at the World in a Different Light

All warm objects (not just people) release infrared light. Warmer objects give off more infrared light. Very hot objects radiate other types of light as well. Click on the picture to see the infrared...more

ExploraTour - Looking at the World in a Different Light

What kinds of light can people see? Our eyes can see visible light. When it passes into our eyes different types of visible light create different sensations that we see as colors. ...more

ExploraTour - Looking at the World in a Different Light

Imagine you found a pair of special glasses that not only gave you telescopic vision but gave you the ability to see all forms of radiant energy. The universe in visible light contains all the familiar...more

ExploraTour - Looking at the World in a Different Light

This is a volcano on the island of Miyake in Japan. It has erupted, sending hot lava and ash into the air, a total of ten times. The time after one eruption until the next occurred was about twenty years...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA