The Theory of Evolution

The Theory of Evolution
In science, theories are statements or models that have been tested and
confirmed many times. Theory, for science purposes, does not express doubt. The
word theory is used to represent ideas & explanations that have been confirmed
through numerous tests and observations.
Theories have some important properties:
• They explain a wide variety of data and observations
• They can be used to make predictions
• They are not absolute, they serve as a model of understanding the world and can
be changed as the world view changes
Ex: The theory of evolution remains one of the most useful theories in biology
because it explains many questions and observations. It is considered a unifying
theory of Biology.
Some questions that can be answered by evolution.
• Why do so many different animals have the same structures, Ex: the arm bones
in a human are the same bones as a flipper in a whale?
• Why do organisms have structures they no longer use, like the appendix in a
human, or non-functioning wings in penguins?
• Why are there bones and fossil evidence of creatures that no longer exist?
What happened to these creatures?
• Why do so many organisms' morphology and anatomy follow the same plan?
• Why is the sequence of DNA very similar in some groups of organisms but not in
• Why do the embryos of animals look very similar at an early stage?
Darwin's Theory of Evolution by Natural Selection –
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: "On the Origin of Species by Natural
Selection”. Some of his findings –
1. Variation exists among individuals in a species. The favorable variations were
called adaptations.
2. Individuals of species will compete for resources (food and space).
3. Some competition would lead to the death of some individuals while others would
(survival of the fittest).
4. Individuals that had advantageous variations were more likely to survive and
Darwin's Finches:
Darwin noted that all the finches on the Galapagos Island looked about the same
except for the shape of their beak. His observations lead to the conclusion that all
the finches were descendants of the same original population. The shape of the
beaks were adaptations for eating a particular type of food (Ex. long beaks were
used for eating insects, short for seeds)
Lamarke's Theory of Acquired Characteristics – pg. 376 of text
Some thought 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
• 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.
Lamarke's Theory was eventually discarded - PROVEN 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.
Evidence of Evolution
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.
• Carbon dating – gives an age of a sample based on the amount of radioactive
carbon is in a sample.
• Fossil record – creates a geologic time scale.
Evidence from Living Organisms
• Evidence of Common Ancestry – finch species on Galapagos Islands
• Homologous Structures – structures that are embryologically similar, but have
different functions, such as, the wing of a bird and the forearm of a human
• Vestigial Organs – seemingly functionless parts, snakes have tiny pelvic and limb
bones suggesting they evolved from 4-legged organisms. Humans have wisdom
teeth, because at one time they needed this 3rd set of teeth to grind plants.
• Biochemistry and DNA
• Embryological development – embryos of different species develop almost
Direct Observation of species change
1. wolves/dogs
2. dog breeds