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Unit 5: Evolution
Mr. Chapman
Biology 30
Early beliefs
In the 1700s scientists believed that
organisms were fixed and did not change.
At this time there were a few scientists
who were making major contributions to
the study of biology.
Carl Linnaeus
A Swedish botanist who
proposed a new system of
organization of plants,
animals, and minerals
based on their similarities.
Erasmus Darwin (not Charles!)
An English doctor and
poet who proposed
that all living things
descended from a
common ancestor. He
believed that more
complex things came
from less complex
things.
Lamarck
Jean-Baptiste Lamarck was a
French naturalist
He believed that all organisms
evolved towards perfection and
complexity.
He proposed that changes in an
environment caused an organism’s
behaviour to change. This change
could lead to greater use or disuse
of a particular structure.
Lamarck
Inheritance of Acquired
Characteristics
The idea that the environment could
cause a change in an organism’s
behaviour leading to the disuse or
greater use of a structure. The
structure would then become
larger or smaller, depending on its
use. This change in the structure
would then be passed on to the
offspring.
Inheritance of Acquired
Characteristics
Example:
Lamarck believed that giraffes’ long necks
had evolved over generations because the
giraffes were reaching for the leaves off of
trees.
Charles Darwin
Was born on February 12, 1809 in
England.
He came from a wealthy family, and was
expected to follow a medical career.
After he had graduated from Cambridge
he was invited to go on a voyage on the
H.M.S Beagle.
He went on a five year voyage from 18311836.
Beagle Voyage
They travelled down to the Galapagos
Islands, which are about 600 miles west of
Ecuador.
Galapagos Islands
These islands have species of organisms
found no where else in the world.
Darwin began to study the birds on the
islands. As he studied the finches, he
realized how different they were from one
island to the next.
He identified 13 species of finches.
There was only one species on the
mainland
Darwin’s Finches
They differed in beak size and shape.
Darwin’s Finches
He concluded from this observations that
as the birds dispersed to other islands
they adapted to different environments
and conditions.
They changed in ways that allowed them
to get enough food, in order to survive and
reproduce.
Adaptive Radiation:


Different populations of a species become
reproductively isolated from each other by
adapting to different ecological places.
Eventually they become separate species.
Darwin did not think that the environment
was responsible for the variation.
He believed that the variation existed
before and that nature was just selecting
the most suitable beak shape and size.
Survival of the Fittest
Individuals who have variations that give
them an advantage to survive and
reproduce are the ones who will pass on
their traits more frequently.
Darwin worked on his theory for more than
20 years!
Darwin found out that another naturalist
was also working on a similar theory.
Alfred Wallace was a British naturalist who
was working on his own theory.
After realizing how similar their ideas
were, Darwin and Wallace made an
announcement of their discoveries
together.
Darwin published The Origin of Species in
1858.
Evolution by Natural Selection
There are five main ideas of Natural
Selection:





Overproduction
Struggle for existence (competition)
Variation
Survival of the fittest
Origin of new species (Speciation)
Overproduction
The number of offspring produced by a species is
greater than the number that can survive, reproduce,
and live to maturity.
Example:
Cod fish lay millions of eggs, yet the ocean is not
completely filled with codfish because only a few survive.
A bacterium can divide by binary fission every 20
minutes. In theory one bacterium could give rise to 4 x
1021 cells in just 24 hours!
Competition
Due to overproduction, organisms of the same species, as well as
those of a different species, must compete for limited resources,
such as food, water, and a place to live.
Example:
Paramecium is a single-celled, ciliated protozoan
that feeds on bacteria. There are a number of species of
paramecium. Both species thrive when raised alone.
When raised together, the growth rate is slowed for both,
until one species declines. Evidently these two ciliates
are competing for a limiting resource, share the same
niche, and competition determines that only one persists.
Intra-specific Competition
Competition occurring between organisms
of the same species.
Inter-specific Competition
Occurs when two different species compete for
resources.
http://www.youtube.com/watch?v=LU8DDYz68kM
Variation
Differences among traits occur among
members of the same species. Therefore
no two individuals are exactly alike. These
variations are passed on to the next
generation.
Variations
We now know that variations arise by
mutations.
Mutations occur when there is a change in
a gene’s sequence, or in the number of
chromosomes.
Example
Some jaguars are born with slightly
larger jaws and teeth. This variation will be
passed onto the next generation.
Survival of the Fittest
Those individuals in a species with traits that
give them an advantage (those that are well
adapted to their environment) are better able to
compete, survive, and reproduce.
All others die off without leaving offspring. Only
the strongest organisms survive, reproduce and
consequently leave the strongest offspring.
Example:
Peppered moth of the industrial
revolution.
Speciation (Origin of a new
species)
Over numerous generations, new species
arise by the accumulation of inherited
variations. When a type is produced that is
significantly different from the original, it
becomes a new species.
Example: Darwin’s Finches