Evolution

Evolution

• Definition: Change in a population of organisms over time.

Modern Humans

• Human evolution illustrated on a cladogram

Theories of Evolution

• Jean-Baptiste Lamarck – 1809 published his theory of evolution – Mechanism of

Evolution = Inheritance of Acquired Characteristics

Theories of Evolution

• Charles Darwin – 1859 published his theory of evolution in the major work, On the Origin of Species– Mechanism of Evolution

= Natural Selection

The Original Manuscript

• Most important book on biology ever published!

Lamarck’s Ideas

• Organisms change over time

• Organisms are adapted to their environment

• They are continually changing and acquiring features more suitable for their environment.

• Continued

Larmarck’s Ideas

• During an organism's lifetime, there is selective use or disuse of its organs and traits. If a trait isn’t usedit’s lost.

Larmarck’s Ideas

•Traits that are used are passed on to their offspring. Over time, this process leads to the change in a species. (hence the term: inheritance of acquired characteristics)

Darwin’s Ideas on Evolution

• Variation – organisms show variation in each of their traits: height, colors of eyes/hair/skin, resistance to disease, etc.

• Natural selection – Organisms better suited to their environment survive and reproduce (also known as survival of the fittest).

• Fitness – ability to survive and leave offspring. No offspring = No fitness.

Worksheets

• Natural Selection and fur color

• Evolution: comparison of Lamarck (acquired characteristics) and Darwin’s (natural selection) ideas on evolution.

Darwin’s ideas on Evolution

• In the early 1800’s, when Darwin was born, people thought the Earth was a few thousand years old.

• But by the 1820’s, scientists hypothesized the Earth was millions of years old.

• 5000 years

• 5,000,000 years

Darwin’s ideas on Evolution

• An ancient Earth was necessary to support Darwin’s ideas on evolution—populations change over (long, long periods of) time.

55,000,000YA

35,000,000YA

17-11 MYA

12-6 MYA

5 MYA-present

Microevolution according to

Darwin’s Ideas on Natural Selection

Natural Variation in population of bacteria

Macroevolution according to

Darwin’s Ideas on Natural Selection:

Speciation* –formation of new species

Genes and Variation• Most

phenotypes (traits) are polygenic.

• A graph of these traits often shows a bell curve.

Stabilizing Selection

• If individuals near the center of the bell curve have higher fitness (= leave a greater amount of fertile offspring) then stabilizing selection occurs.

Directional Selection

• If individuals at one end of the bell curve have higher fitness then directional selection occurs.

Disruptive Selection

• If individuals at both ends of the curve have higher fitness than those in the middle then disruptive selection occurs.

Genetic Drift

• If a small population is isolated from others of the same species, it is possible that just be “chance” one allele may become more common in a population.

Genetic Drift

• For example: The Bronx, NY, becomes built up and trees are cut down. Few squirrels are able to survive. However, one section of the Bronx is set aside for the development of the Bronx Zoo. Trees are NOT cut down in this area. By chance, several of the gray squirrels in the area of the zoo have black fur (a variation in fur color). Over time, the allele for black fur becomes common in this population.

I’ I’m an Eastern Gray

Squirrel

I’ I’m an Eastern Gray

Squirrel

How do new species form?Example: Galapagos Finches

• A small group of a species of finch arrives on one of the Galapagos Islands

• These finches do not usually fly across open water—they may have gotten lost or were blown there by the wind.

Speciation continued!

• Over time these original finches may have ended up on other of the Galapagos Islands through some chance occurrence.

• USUALLY the finches do NOT fly from one island to another.

Speciation continued!

• The Galapagos Islands had different environments. – Some had a low elevation and were dry with

little plant material.

Speciation continued!

• Others had a higher elevation with greater rainfall and many plants.

Speciation continued!

• Directional selection occurs:– One island may have seeds that are large and

difficult to open. – Birds with a larger, thicker beak will have the

highest survival rate on this island

Speciation continued!

• Directional selection occurs:– Another island may have seeds that are small

and easy to open – Birds with a small, thinner beak will have the

highest survival rate on this island

Speciation continued!

• Reproductive Isolation: if the populations remain separate, and their gene pools continue to change, eventually they can no longer mate with each other—they are then TWO NEW SPECIES!!!

• On the Galapagos Islands this processes resulted in the evolution of 13 different finch species.

Darwin’s Finches

Evidence of Evolution

• Fossil Record

Evidence of Evolution

• Comparative Anatomy: – Homologous structures = structures that have

different mature forms but develop from the same embryonic tissue

Evidence of Evolution

• Vestigial organ = organ that serves NO useful function in an organism.– Wisdom teeth– Appendix

HUMANS

Fingernails on Seal’s Fin

Embryology

NOTE Similarity of embryos of all of these animals

Evidence of Evolution

• Similarities and dissimilarities in DNA code.

• Complete worksheet + bar graph.