Evidence for Evidence for EvolutionEvolution

“There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have

been, and are being evolved."

-Charles Darwin, Origin of Species (1859)

II. Evolution: Fact or Theory?

A. Define Fact: Has undergone repeated tests over a period of time. More certain than a theory.

B. Define Theory: Not yet “proven”. A collection of carefully reasoned and tested hypotheses, supported by evidence.

I. What is Evolution? The process by which modern organisms have

descended from ancient organisms

C. Examples - Fact or Theory?

1. Gravity exists.

• There is no doubt that gravity does exist. What goes up, must come down, right!

• However, physicists do not completely understand how gravity works!

2. Life on Earth has changed over time.

• There is no doubt that life on Earth does change over time.

• However, explaining how life changes over time continues to be one of the great challenges of biology.

Sir Isaac Newton

Charles Darwin

III. Evidence for Evolution

A. Similarities in Early Development

1. Embryos of many different animals are similar in appearance, especially during the early stages of development.

The similarities of vertebrate embryos show that similar genes are at work

Bio pg. 283

B. Similarities in Body Structures

1. Homologous Structures - parts of different organisms that developed from the same ancestral body part

Examples: The limbs of various vertebrates are similar in structure

Bio pg. 284

2. Vestigal Organs - Organs that are so reduced in size or function that they are merely traces of similar organs in other species

Examples:

• tail bone and appendix in humans

• tiny bones on the underside of pythons and boa constrictors

Bio pg. 285

C. Similarities in Chemical Compounds

1. Genetic Material: All organisms, from bacteria to humans, use DNA and /or RNA to carry information from one generation to the next

Example: DNA of all eukaryotic organisms has the same structure and replicates in the same way

DNA RNA

D. The Fossil Record

1. Species have gone extinct

Example: Dinosaurs

2. New species have developed

Example: Homo sapiens

3. Species have changed over time

E. Observed Evolution

1. Examples:

Drug resistance in bacterial strains

Insecticide resistance

England’s Peppered Moth

Darwin’s Finches

Bio pg. 297

IV. How Does Evolution Occur?

A. Early Theories

1. Jean Baptiste de Lamarck (1744-1829) was one of the first scientists to recognize that living things change over time

a. Early Theories used by Lamarck

A Desire To Change - Organisms change because of an inborn urge to better themselves. (ex. Birds really wanted to fly!)

Use and Disuse - Organisms could alter their shape by using their bodies in new ways (ex. Organs would increase in size if they were used a lot and vice versa)

Passing on Acquired Traits - Acquired characteristics are passed on to future generations

2. Charles Darwin and The Beagle

a. Christmas 1831, a young Englishman named Charles Darwin set sail on the Beagle for a 5 year cruise around the world

b. Darwin’s keen observations, data collection and analysis remain the foundation for evolutionary theory today

B. Darwin’s Theory of Natural Selection-The process by which the organisms whose characteristics are well-suited for their environment survive and reproduce.

1. The Three Steps of Natural Selection

(1) Variation:

Gene mutations and recombinations provide the variation upon which natural selection acts

(2) Selection:

In the struggle for existence, organisms either survive and reproduce or do not.

Far more organisms are born than ever grow to adulthood

Those organisms with adaptations well-suited for the environment are “selected” to survive

(3) Reproduction:

Best-fit organisms have the highest probability of successfully reproducing

Favorable characteristics (adaptations) will be passed on to the offspring

Organisms in future generations will become better and better adapted to their environment

2. Evolutionary Fitness

In summary, each time an organism reproduces it passes copies of its genes to its offspring.

Evolutionary Fitness: the success an organism has in passing on its genes to the next generation.

Note: Evolution occurs only if genes (and traits) are passed on and measured in future generations!