Darwin and Evolution
17.1 History of Evolutionary Thought
1. In 1831, Charles Darwin, a 22-year-old naturalist, accepted
a position aboard the ship HMS Beagle that began a voyage
around the world; it provided Darwin with many observations.
In a lofty valley of the Cordillera, near Mendoza, I
found another spider with a singularly-formed
web. Strong lines radiated in a vertical plane from
a common centre, where the insect had its
station; but only two of the rays were connected
by a symmetrical mesh-work; so that the net,
instead of being, as is generally the case,
circular, consisted of a wedge-shaped segment.
All the webs were similarly constructed.
Excerpt from "The Voyage of the Beagle" by Charles Darwin
Pre-Darwinian world-view was determined
by theological beliefs.
1) The earth is young.
2) Each species was specially created and
did not change
3) Variations are imperfections
4) Observations are to substantiate the
prevailing worldview.
2. Mid-Eighteenth-Century Contributions
Carolus Linnaeus and Taxonomy
Taxonomy is the science of classifying organisms;.
Linnaeus developed a binomial system of nomenclature two-part names for each species
Homo sapiens
Canis lupus
Brassica rapa
B. Georges Louis Leclerc
Count Buffon (1707-1788), was a French naturalist.
In the course of his examination of
the animal world, Buffon noted that
despite similar environments,
different regions have distinct
plants and animals, a concept later
known as Buffon's Law, widely
considered the first principle of
biogeography.
C. Erasmus Darwin
a. Erasmus Darwin (1731-1802) was Charles Darwin's grandfather.
b. He was a physician and a naturalist whose writings on both
botany and zoology contained many comments that suggested the
possibility of common descent.
3. Late Eighteenth-/Early-Nineteenth Century Contributions
A. Cuvier and Catastrophism
a. George Cuvier (1769-1832), a French vertebrate zoologist, was the
first to use comparative anatomy to develop a system of classifying
animals.
b. He founded the science of paleontology-the study of fossils-and
suggested that a single fossil bone was all he needed to deduce the
entire anatomy of an animal.
c. To explain the fossil record, Cuvier proposed that a whole series of
catastrophes (extinctions) and re-populations from other regions had
occurred.
d. Catastrophism is the term applied to Cuvier's explanation of fossil
history: the belief that catastrophic extinctions occurred, after which
repopulation of surviving species occurred, giving an appearance of
change through time.
B. Lamarck's Acquired Characteristics
a. Lamarck (1744-1829) was the first to state that descent with modification
occurs and that organisms become adapted to their environments.
b. Lamarck, an invertebrate zoologist, held ideas at odds with Cuvier's.
c. Lamarck mistakenly saw "a desire for perfection" as inherent in all living
things.
d. Inheritance of acquired characteristics was Lamarck's belief
that organisms become adapted to their environment during
their lifetime and pass these adaptations to their offspring.
e. Experiments fail to uphold Lamarck's inheritance of acquired
characteristics
How could you test
Lamarck's theory?
What We Know So Far
1. Taxonomy and classification emphasize similarities among
species (common descent)
2. Fossils show extinct species (paleontology)
3. Isolated species are distinct (biogeography)
4. Organisms have adaptations to help them survive
*At this point, no mechanism has been proposed to explain how
these adaptations come to be
* Special creation is still strongly held,
but offers no explanation for the
appearance of new species (like on an
island)
.........Enter Charles Darwin..........
17.2 Darwin's Theory of Evolution
The Voyage of the Beagle
4. Galapagos
●Islands off S. America
●Island species varied from mainland species
●Finches resembled mainland finches, but with more
variation
●Tortoise Variations
Figure 17.7a
Dome shells, short necks - feed at ground level
Figure 17.7b
Shells that flare up, long necks - feed on tall plants
Marine Iguana
5. Darwin's Finches
a. Finches on the Galápagos Islands resembled a mainland
finch but there were more types.
b. Galápagos finch
species varied by nesting
site, beak size, and eating
habits.
Vampire Finches?
Questions to Ponder:
Did the animals on the islands
descend from one mainland
ancestor?
What were the variations found on the finches?
Why were the island finches so different from
mainland finches?
Why did the vampire finch evolve?
6. Natural Selection and Adaptation
a. Natural selection was proposed
by both Alfred Russel Wallace and
Darwin
Wallace was not given credit for the
theory because Darwin published
first, however, there is a
geographical area named for him
called the "Wallace Line" which
separates Australia and Asia.
Figure 17B
Regions between Australia and the Orient have
distinct biogeography – separated by what we now
call the Wallace Line
There are three preconditions for natural
selection.
1. The members of a population have random but
heritable variations.
2. In a population, many more individuals are
produced each generation than the environment
can support.
3. Individuals have adaptive characteristics that
enable some to survive and reproduce better.
Consider This.....
What characteristics might make
these rats more likely to survive?
There are two consequences of natural selection.
1. An increasing proportion of individuals in succeeding
generations will have the adaptive characteristics.
2. The result of natural selection is a population adapted to its
local environment.
Natural selection can only utilize variations that are randomly
provided; therefore there is no directedness or anticipation of
future needs.
Pause and think: Thinking that evolution has a direction is a
common misconception.
Can you think of any statements you may have heard that
suggest people think that evolution is directional?
Extinction occurs when previous adaptations are no longer
suitable to a changed environment.
How Evolution by Natural Selection Works
1. Variations exist in a
population.
2. Every individual struggles to exist.
3. Individuals differ in FITNESS
a) fitness measures an organism’s reproductive success
b) it does not necessarily mean stronger.
Fully armored
stickleback (ocean)
Low armor (freshwater)
4. Survivors pass traits to offspring
Over time, the traits that provide the best chance of survival
and reproduction are the ones most prevalent in the
population - these are ADAPTATIONS
Be careful with that word…..
Adaptation is a trait, a noun.
It is dangerous to use it in verb form because it suggests that
an individual can choose to adapt. They cannot.
***** POPULATIONS EVOLVE *****
Individuals are pretty much stuck with the traits they have
inherited.
Fix this sentence:
This Aye Aye has adapted to a life
of eating insects. It’s long digit is
used to probe wood.
ARTIFICIAL SELECTION
Dogs breeds were
developed by years of
breeding wolves
We chose the traits
most desirable, then
bred the dogs with
those traits.
Nature does the same
with “natural selection”
ARTIFICIAL SELECTION IN PLANTS
All of these species came from one species
On the Origin of Species by Darwin
1. After the HMS Beagle returned to England in 1836, Darwin
waited over 20 years to publish.
2. He used the time to test his hypothesis that life forms arose
by descent from a common ancestor and that natural selection
is a mechanism by which species can change and new species
arise.
3. Darwin was forced to publish
Origin of Species after reading a
similar hypothesis by
Alfred Russel Wallace.
The Definition of Evolution
Evolution is the change in allele frequencies,
or a change in the gene pool, of a population.
Things that are evolution.
Things that are NOT evolution.
Imagine a Scenario of Evolution.....
1. Create a real or imagined organism
2. Describe 2-3 variations
3. Show how evolution would act on this population given a
change in the environment (climate, predators, food change..)
4. Pay attention to which variations are beneficial, which are
harmful.
5. Show how reproduction changes the overall population
(with regard to these variations)
6. Be creative! You can map your organism through a few
generations... You will present your scenario to the class!