1. Unit A: Biological Diversity Topic 6: The Best Selection

2. Artificial Selection  Occurs when humans purposely breed a species to select for a specific trait/allele/gene.  When you are selecting a trait, you are also selecting the genes that code for that trait.  For example, with dogs, the behavioral trait of obedience has been selected for over thousands of years with the result that dogs are able to be tamed, but wolves, and coyotes cannot.

3. Artificial Selection  Upside: Can result in major genetic changes to a species much faster than would happen if evolution occurred naturally.  Downside: By selecting for traits that we think are good we produce organisms that are no longer adaptable to their environment and would die without us.  Downside: By selecting for only a few traits we are reducing the variability in a species.  Downside: Artificially selecting for only a few traits can have harmful side-effects in organisms (Eg. deafness in Dalmatians)

4. First Example of Artificial Selection  Occurred in the Fertile Crescent (Middle East) 10000 years ago.  Hunter/gatherers noticed that certain plants contained high energy levels.  These plants were artificially selected for size and energy. This is the beginning of farming, and cities, and civilization.

5. Artificial Selection Example Cont’d  Because of farming, wheat, corn, and rice make up over half of all domestic plants. The variability in these species of plants has been greatly reduced. These plants are being artificially selected (called selective breeding in farming) and genetically engineered for disease resistance. However, the lack of variability is troubling.

6. Charles Darwin  Lived in 1800s England.  Travelled to the Galapagos Islands and noticed that similar species of birds on different islands looked and acted different from each other.  Wrote the book, Origin of Species by Means of Natural Selection.

7. Theory of Natural Selection  All organisms and species compete with each other for survival and the opportunity to reproduce.  Natural selection says that the environment selects for organisms which are best fitted to that environment.  This process is very slow, taking millions of years, and thousands of generations.

8. The Four Rules of Natural Selection 1. All organisms produce more offspring that can possibly survive. This leads to increased competition and survival of the fittest. 2. There is incredible variation within a species. 3. Some of these variations increase the chances of an organism surviving to reproduce. 4. Over time, variations that are passed on lead to changes in the genetic characteristics of a species.

9. What Natural Selection Doesn’t Say  Natural selection doesn’t select for the most intelligent, the strongest, or most ‘beautiful.’ It only says that animals that have adaptations that help it survive and reproduce in its environment will have a better chance than others to pass on their genetic code.  There is no end point with natural selection, as the environment changes, so does which traits become favoured.

10. The Peppered Moth and Natural Selection  White colored moths had a better chance to survive and reproduce than black moths because most trees in their environment (England) were covered in white lichen.  Air pollution in the 1800s blackened the lichen and this feature selected for black colored moths.  100 years later, when pollution was cleaned up, white moths were again selected for, and black moths selected against.