Natural Selection - How do plants and animals evolve? Why do they change in useful ways?
Welcome to Study Guides!

Natural Selection

A foot with six toes
A mutated foot with six toes

Whenever protons and electrons bump into each other, or atoms bump into each other, or molecules bump into each other, or prokaryotic cells bump into each other, or DNA molecules inside cells divide - whenever any of these things happen, they can happen in any of several ways, and random chance means that they do happen in lots of different ways. But some of these ways work better than others.

Say six protons bump into each other by chance - their forces will push them apart again, so they won't form an atom. But suppose one proton and one electron bump into each other - then their forces will naturally pull them together, so they form a hydrogen atom.

Now say some of those hydrogen atoms happen to bump into a helium atom. Nothing will happen, because the helium atom is stable on its own and can't bond with hydrogen. But if the hydrogen atom happens to bump into a carbon atom, they'll naturally bond together to make a hydrocarbon molecule (like sugar or oil). A hydrocarbon molecule is chemically strong, or stable - it's hard to break it apart. So more and more of the hydrogen and carbon atoms end up in hydrocarbon molecules.

Now suppose some of those hydrocarbon molecules happen to bump into some oxygen and nitrogen atoms - then they might happen to link up and become amino acids. Not all the hydrocarbons become amino acids; some stay just plain hydrocarbons. Some break down again into hydrogen and carbon atoms.

After some time, suppose gravity happens to pull a few of these amino acids floating around out in space down to a new planet, Earth. Here on Earth something new is happening - instead of the cold ice of space or the blazing heat of stars, there is warm water, heated by underwater volcanoes. The warm water makes different chemical reactions happen here, and some of the amino acids begin to bump into each other and stick together to make bigger and bigger molecules that we call RNA and lipids, and to make new molecules called proteins.

More about natural selection - from RNA to modern plants and animals

Bibliography and further reading:

Math home
Celebrating Black History Month with the pharaoh Hatshepsut, the queen Shanakdakhete, the poet Phillis Wheatley, the medical consultant Onesimus, the freedom fighters Toussaint L'Ouverture, Denmark Vesey, Yaa Asantewaa, and Samora Moises Machel, and the civil rights leader Martin Luther King, Jr.
Please help other teachers and students find us: link to this page from your class page.
Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram or Twitter.
Cite this page
  • Author: K.E. Carr
  • Title:
  • Site Name: Study Guides
  • Publisher:
  • Date Published:
Proud of your class page, homework page, or resource page? Send it in and win a "Great Page!" award!
Sign up for more free articles and special offers in' weekly newsletter:
We will never share your e-mail address unless you allow us to do so. View our privacy policy. Easy unsubscribe links are provided in every email.
Comment on This Article

Cool stuff we've been enjoying: Looking for birthday gifts? Check out these new Chromebooks - all the computer you need for only $229.00!. Then study in peace with these Beats wireless headphones - for the exact same price! When you're done, show off your presentation or watch a movie with this excellent smartphone projector for only $39.99!

Does your class page honor diversity, celebrate feminism, and support people of color, LBGTQ people, and people with disabilities? Let us know, and we'll send you a Diversity Banner you can proudly display!
Looking for more?
ADVERTISEMENT is loading comments...
(Comments will appear after moderation, if they are kind and helpful. Feel free to ask questions, and we'll try to answer them.)
Cite this page
  • Carr, K.E. . Study Guides, . Web. 23 February, 2017