Download A-6 Notes

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