"nothing in biology makes sense except in the light of evolution”

~Theodosius Dobzhansky (1900-1975)

Photo by “davemee” flickr creative commons

•In science, theories are statements or models that have been tested and confirmed many times.

In science, the term "Theory" does not express doubt.

•They explain a wide variety of data and observations

•They can be used to make predictions

•They are not absolute, can be changed as new evidence is found

•Why do so many different animals have the same structures: for example, the arm bones in a human are the same bones as a flipper in a whale?

• Why is the sequence of DNA very similar in some groups of organisms but not in others?

•Why do the embryos of animals look very similar at an early stage?

Photo courtesy of Swamibu, Flickr Creative Commons

1. Variation exists among individuals in a species.2. Individuals will compete for resources (food, mates, and space)3. Competition would lead to the death of some individuals while others would survive4. Individuals that had advantageous variations are more likely to survive and reproduce.

This process came to be known as Natural SelectionThe favorable variations are called Adaptations

Photo courtesy of digitalART2, flickr creative commons

What is an adaptation?

An adaptation is a genetic feature that is common in a population because it provides some improved function that helps members of the population survive and reproduce.

Examples:• Physical characteristics—giraffe’s long neck• Behavioral characteristics—lions stalking prey• Internal characteristics—cheetah’s extra large heart that helps

them run fast

What an adaptation is not• Adaptations are not acquired through practice or use.

Organisms only pass on what is in their genes. If you practice basketball and become excellent at it, you cannot pass that on to your offspring!

• Adaptations do not arise because they are needed.

Adaptations arise from chance mutations that are passed on when their helpful function helps organisms survive.

•Say in a species of blob….there exists blobs of all shapes and sizes (variation)

Blobs eat the little purple organisms that live underground and on the surface.

During a particularly hot year, food became less abundant (competition), blobs that had the ability to dig into the soil to get food had a better chance of survival.

Many blobs died that year…….

The ones that survived mated and passed their genes to the next generation. (reproduction)

The next generation had more blobs with the pointed noses. That is NATURAL SELECTION.

1.Variation2.Competition3.Survival4.Reproduction

Fossil Evidence•Shows numerous extinct animals

•Shows similarities between extinct animals and animals that are alive today

•The earth’s layers show a time scale of species and when they appeared on earth (and when they died out)

•Homologous structures – these are parts of the body that are similar, but have different functions

ex. The flippers of whales, and the wings of birds

All forelimbs of vertebrates have the same pattern of bones

• Common ancestry

•Vestigial Organs – these are organs or parts that seem to have no function

Whales have pelvic bones that do not attach to legs

Human tailbones serve no current purpose.

•Biochemistry and DNAWhen comparing the DNA of one species to another, more similarities are found in species that are more closely related.

Lion photo credit: ucumari Tiger photo credit: digitalART2

Chimpanzees and bonobos share over 98% of their DNA with us!

Embryological DevelopmentEmbryos of different species develop in almost identical ways.

Human fetus at 8 weeks

Direct observation of species change 1.Bacteria become resistant to antibiotics

2.Wolves were bred over many generations to become dogs (artificial selection)

• and then bred further to create a variety of breeds