Download MECHANISMS AND PATTERNS OF EVOLUTION

MECHANISMS AND PATTERNS OF EVOLUTION
Evolution in Modern Times:
There are some organisms that evolve in short periods of time. These organisms have
short reproductive cycles such as pathogens in an antibiotic environment and insects in a pesticide
environment. Because of this, scientists can study the mechanisms and patterns of evolution in
progress. It is important to remember that organisms do not change their characteristics in direct
response to the environment. The genetic variation existed within the population along with the
potential for new combinations of traits. Nature selects those individuals that have traits that
will survive in a changed environment. If the organism can successfully reproduce, the trait will
be passed on to future generations.
Recent Examples of Evolution:

Use of Pesticides –
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Use of Antibiotics –
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English Peppered Moth –
~ observed in England for over 100 years
~ two basic colors of moth – light and dark
~ before Industrial Revolution – more ___________________ moths observed,
which was an advantage because __________________________________
~ after Industrial Revolution – more ____________________ moths observed
WHY???
~ most recently, there has been a change back to _____________________ moths
because of environmental laws limiting the amount of pollution let in air

Behavioral patterns are also thought to have evolved through natural selection
Adaptive Radiation:

Adaptive radiation is the process by which many new species of organisms evolve
from a common ancestor

The new species evolves and fills different environmental niches where there is less
competition. A niche is the role an organism plays in a particular environment. A
niche includes

Organisms move into new niches in the environment through chance mutations that
have positive adaptive value. A favorable adaptation would be one that allows an
organism to live a reproduce in a new environment.

Ex - Darwin’s Finches
Geographic Isolation:

Geographic isolation occurs when a population is physically separated into smaller
populations by geographic barriers

Natural barriers include –

Human created barriers include –
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Changes may occur in these separated populations that over a period of time, may
result in the production of different species (speciation)

Speciation occurs when members of the
isolated population and the main population can no longer interbreed, even if the
barriers are removed – this is known as reproductive isolation
Selective Breeding:

Selective breeding methods involve mating organisms with a particular desirable trait
to produce offspring with this trait

EX – racehorses have been produced that are faster than their ancestors

By selective breeding, man may cause evolution

In natural selection, ___________________________ acts as the selecting agent, but
in artificial selection, __________________________ are the selecting agents.
Rate of Change:
Although most scientists agree on the current facts of modern evolution theory, they do
not agree on the time frame for evolutionary change.
Time Frame for Evolutionary Change
(1) Gradualism – A theory that proposes that evolutionary change is slow, gradual, and
continuous. New species would arise by the very gradual collection of minor changes in a
population
(2) Punctuated Equilibrium – A theory that proposes that species are relatively stable for long
periods of time (several million years). This stability is interrupted by brief periods during which
major changes occur. These changes result in the evolution of new species.
These two time frames can be drawn as graphs.
Gradualism:
Punctuated Equilibrium:
Studying Human Evolution:
Scientists know very little about human evolution. One reason is that there is very little
fossil evidence. Some people incorrectly think that Darwin proposed that humans evolved from
apes. Darwin only suggested that humans, along with other mammals, could have shared a
common ancestor.
Modern scientists assume that human evolution, like evolution in other animals, is
continuing. However, because of their superior reasoning ability, humans are able to control their
environment. Because of this, the evolutionary effect of natural selection is not as great as in
other organisms. Factors that affect or may affect human evolution are reviewed below.
Factors That Affect or May Affect Human Evolution

Medical Knowledge. Medical knowledge permits the survival of individuals with
genetic traits such as diabetes, hemophilia, and PKU. Without medical knowledge
these people would die and the genes for these diseases would decrease in number in
the population. With modern medicine, the number of genes are maintained or
increased.

Modern Transportation. Due to modern transportation, humans are less affected by
the evolutionary force of geographic isolation.

Advanced technology. Advanced technology has given humans better nutrition and
greater control over their reproductive process. It also has increased the number and
kinds of mutagenic agents in the environment.

Genetic Engineering. Genetic Engineering may possibly lead to the appearance of
new traits and the elimination of others.