Download An Introduction to Evolution

Bio 20 - Evolution
Teacher Notes
An Introduction to Evolution
The Theory of Evolution remains one of the most useful theories in biology
because it explains many questions and observations, such as:
 Why do organisms have structures they no
longer use, like the tail bone in humans or
non-functioning wings in penguins?
 Why do so many different animals have the
same structures, such as arm bones in
humans are the same bones as a flipper in a
whale?
 Why are there bones and fossil evidence of
creatures that no longer exist? What
happened to these creatures?
Evolution – hereditary changes in groups of living organisms over time
Evidence for Evolution
1. Fossil Evidence
If today’s species came from ancient species, then we should be able to find
remains of those species that no longer exist.
We have tons of fossils of creatures that no longer exist but bear striking
resemblance to creatures that do exist today. In other words, fossils provide
evidence of the change in organisms.
Fossil – preserved evidence of an organism
Plants, animals, and bacteria can form fossils but most die and decompose before
they have a chance to become fossilized.
Bio 20 - Evolution
Teacher Notes
Fossils are usually found in sedimentary rocks. Because younger rocks often lie on
top of older rocks, scientists can determine the course of changes in living things
on Earth.
Carbon dating also gives an age of a sample based on the amount of radioactive
carbon is in a sample.
Fossil record – creates a geologic time scale that indicates life forms has changed
with time.
Paleontology – the study of prehistoric plants and animals through the fossil record
Bio 20 - Evolution
Teacher Notes
2. Evidence from Living Organisms
Vestigial Organs – body part which has no apparent use today but has some use in
the past.
Examples:
 Snakes have tiny pelvic and limb bones
 Humans have a tail bone
 Pigs, cattle, deer, and dogs have reduced,
nonfunctional digits, referred to as dewclaws. The
foot of the pig has lost digit 1 completely, digits 2
and 5 have been greatly reduced, and only digits 3
and 4 support the body.
Homologous Structures – body parts that are similar in structure but differ in
functions although the origin of the structure was the same.
Example: forelimb of tetrapods (vertebrates with legs)
Bio 20 - Evolution
Teacher Notes
Analogous Structures - body parts that have similar function but differ in
structure.
Embryology – animals having a backbone (vertebrates) appear to have similar
structures as embryos.
Bio 20 - Evolution
Teacher Notes
Biochemical Evidence – chemical analysis of DNA indicates that organisms share
common traits at the molecular level
Theories of Evolution
Two major theories have been put forth:
1. Lamarck’s Theory of Acquired Characteristics
Chevalier Lamarck believed that you would gain
or lose features if you overused or didn’t use
them, and you could pass these new traits onto
your offspring.
This was known as the Inheritance of
Acquired Characteristics.

Lamarck believed that the long necks of
giraffes evolved as generations of
giraffes reached for ever higher leaves.

A lizard that didn’t use it legs would eventually
not have legs and its offspring wouldn’t have
legs
A giraffe stretched its neck to reach higher
leaves, and this stretched neck would be a
trait inherited by its offspring
Lamarck’s Theory was eventually discarded – Demonstrated TO BE WRONG!
Why? Logically it doesn’t work. Imagine if you were in a car accident and had a leg
amputated. This does not mean that your children will only have one leg. Features
gained during life are not passed on to children.
Bio 20 - Evolution
Teacher Notes
2. Darwin’s Theory of Evolution by Natural Selection
Charles Darwin was a naturalist who observed many species. He is famous for his
trips to the Galapagos Islands, his observations of the finches (and other animals)
and the book he wrote: “The Origin of Species”. Darwin’s Theory of Evolution is
based on Natural Selection, which is comprised of:
1. Variation exists among individuals in a species.
2. Competition - Individuals of species will compete for resources (food and space).
3. Overpopulation – Organisms produce more offspring than can actually survive in
a given environment.
4. Survival of the Fittest - Individuals that had advantageous variations are more
likely to survive and reproduce.
Other Evolutionary Scientists
Darwin was inspired by an essay written by Thomas Malthus, an English biologist,
which suggested that nature allows organisms to overproduce which creates a
natural struggle to survive.
Alfred Wallace, a British biologist working in the East Indies, also suggested a
theory of evolution very similar to Darwin’s although it was developed completely
independently. Wallace allowed Darwin to receive total credit for the same theory
of evolution.
Bio 20 - Evolution
Teacher Notes
Lamarck Vs Darwin
Lamarck’s Hypothesis:
Organisms
present
Changes in
environment
Organisms
change
response to
environment
Organisms
survive
Changes in
environment
Organisms with
certain features
are naturally
selected
Certain
organisms
survive
Darwin’s Hypothesis:
Populations of
organisms with
variations
present
Lamarck




Use and Disuse
Transmission of
Acquired
Characteristics
Increasing
Complexity
No Extinctions
Darwin
Both
Change
occurs
in
nature




Variation
Inheritance
Differential
Survival
Extinction