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Avatar: Species Can Change
Slide 1
From the fossil record, we know that species can change over time. Biological evolution
describes the changes in living things over generations of time. The process of a species
changing over time through biological evolution begins with the development of genetic variations
within the species.
Here you see an example of variation in a flower that is normally yellow, but one of them has
developed a mutation that manifests an orange color instead. Variations like this develop from
mutations, which are random changes in the structure or number of DNA molecules in a cell that
can be inherited by offspring. Mutations that occur in an organism’s reproductive cells are passed
on to its offspring. The offspring then have some trait different from what is normally seen in its
population.
In summary, species may change over time through biological evolution, and evolution is driven
by genetic mutations that get passed from one organism to its offspring.
Slide 2
Some mutations are lethal. Imagine, for example, a mutation in humans that leads to a
development of cancer. Other mutations can be helpful, such as one that helps an insect hide
from birds that eat it, by causing the insect to have colors that blend in with the local environment.
Can you spot the insects on these tree branches?
Other mutations are somewhere in between—like this example. How many fingers are in this
human hand?
The result of beneficial mutation is a new genetic trait that gives an individual a better chance for
survival than those individuals without the mutation. Those individuals go on to reproduce,
passing the traits to more individuals, and over time the species as a whole takes on a different
look.
Slide 3
Through beneficial mutations, some members of a population have better chances of surviving
and producing offspring than others. This better chance for survival occurs only if the trait
associated with the mutation gives the organism some kind of advantage in its environment. This
gives rise to the next step of biological evolution: natural selection, an idea first presented by
Charles Darwin. Natural selection occurs when some individuals of a population have genetically
based traits that increase their chance for survival. They reproduce and pass that trait on to their
offspring. For several generations, the beneficial traits increase in number within a population.
You may have heard about how overuse of antibacterial soaps and medications has led to the
creation of superbugs that are resistant to being killed.
This diagram shows how natural selection works in a population of bacteria. You start out with a
group of bacteria. They reproduce and some of them develop mutations that make them resistant
to antibacterial products. Those with the mutation have a better chance of surviving and
differential success in reproducing. They then reproduce and pass their high level of resistance
on to their offspring. Later, a new generation emerges that all has all the higher resistance to
antibacterial products. Note that natural selection occurs on individuals but evolution takes place
at the species level.
© KC Distance Learning Slide 4
In summary, natural selection is the process by which favorable traits increase over time in a
population due to differential success in reproduction. It results in species that are better adapted
to their environment or that can better survive pressure from their environment. It gives rise to a
gradual change in a species over time. Natural selection is the process responsible for the great
diversity of life on Earth.
© KC Distance Learning