Natural Selection Image Map

Why Sex Matters

Why do some organisms have sex?  

Bacteria usually reproduce asexually, which produces two identical copies of the parent cell.  Why don’t humans or other animals also use this form of reproduction?  The answer: genetic diversity.  Sexual reproduction allows populations of organisms to be different from one another.  Why would this be adaptive?  Because when ecosystems change, a population  made up of non-identical members has a considerably greater chance to adapt and respond to change in a positive way. By the way, even bacteria have a sex-like mode in which they occasionally fuse and exchange DNA.

Sexual reproduction has another importance.  Members of the population must have sex in order to create offspring.  Obviously, this means that for populations to survive, individuals must live long enough to reproduce.  As you will see in the What We Know section, this is the main requirement of all species.

When humans interfere…

Why do we call this unit "Population Balance?" …Because our world isn’t just a collection of independent groups of populations.  It’s a fragile, global network of interaction.   
Have you ever played the game JENGA®?  Well, Milton Bradley may not have known it at the time, but they created an excellent model of how ecosystems work!  In the game, removing a piece from the stack weakens the stability of the entire structure.  And as more blocks are removed, the stack weakens and will eventually fall apart.

In nature, removing a block could be equivalent to the extinction of a species.  When this happens, every member of the complex ecosystem involved is in danger, and most of the time, this includes humans as well.

Species Diversity - Who Cares?

Why does it matter if species go extinct? Who should care if the number of species on earth decreases? Several answers come to mind. Practical applications in medicine and agriculture often result from discovering unique properties of species, and the more species there are the greater the potential for finding useful genes. These genes can be inserted into existing organisms to produce medicine, disease resistance properties, growth enhancement, and other desirable things.

Human activity is creating massive extinctions. Only a few areas on earth support highly diverse species. Nearly one half of the earth's plant species and over 1/3 of the vertebrate species are found in only 25 local areas. To learn more about these diversity "hot spots," click here.




Introduction | Why It Matters | How We Find Out | What We Know | Story Time
Common Hazards | Activities | Self-Study Game | Teachers Pages | Standards (TEKS)

Peer Curriculum | Ecosystems Home Page | Communication Exercises
Copyright © 2001-2003
Web Site Privacy Statement