Evolution

•  Definition (memorize this!!) :

–  Gradual change in the genetic makeup of a species over a long period of time

Charles Darwin(1809 – 1882)

•  Darwin was always interested in the natural world. He came from a wealthy family and was expected to be a doctor. He went to college to study medicine and hated it…he dropped out. In 1827 he went to Cambridge to study theology and become a minister. Still, he was more interested in the natural world.

The voyage that changed everything

•  At the age of 22, Darwin was hired to be a naturalist on board a survey voyage. The ship was the HMS Beagle. The Beagle was a survey ship that was sent to collect information about the coastline of South America.

http://www.oum.ox.ac.uk/learning/htmls/darwin.htm

On the voyage he read a book by a geologist (Charles Lyell’s Principles of Geology) The book theorized that the surface of the earth changed slowly over many years. Using this information, not only did Darwin realize that the earth must be very old, but he became convinced that the same thing (gradual change) happened to species.

What he observed on the voyage

•  The animals and plants in South America looked more like each other than the plants and animals in similar climates in other parts of the world. S. A. fossils looked like current S. A. plants and animals. Plants and animals found on islands close to South America (Galapagos Islands) were similar to the ones on the mainland.

After the voyage

Darwin returned from the voyage and studied his notes along with other scientists’ essays. Published his observations in a book On the Origin of Species by Means of Natural Selection in 1859. The book had 2 major points:

·  Organisms have changed over time (Darwin called this “descent with modification”. We call it evolution)

·  Organisms change because of natural selection.

Natural Selection

•  Darwin studied Artificial Selection – We have bred animals and plants to suit purposes…we select the traits we like.

Natural selection is also called “survival of the fittest.”

Natural Selection says that individuals that have physical or behavioral traits that better suit their environment are more likely to survive and reproduce than those that do not have such traits.

In order to work the following conditions have to be met:

•  Harsh environment

•  More offspring than can survive

•  Variation within the offspring

Proof of Evolution

•  Five major points that we use to support the theory of evolution:

  1. Fossil Record
  2. Homologous Structures
  3. Vestigial Organs
  4. Amino Acid sequences
  5. Embryology

Fossil Record

Evolution can be seen in the fossil record. Darwin predicted and we have found thousands of “transitional forms” that link ancestors and current organisms.

Examples: page 284 and 285 in your book: whale transitional fossils

Tiktaalik

Significant because it shows transition from fish to amphibian

Also horse transitional forms:

Archaeopteryx

Significant because it shows the transition from reptile to bird.

Homologous Structures

•  Structures that are similar in more than one species and are used to support a common ancestry.

•  Example: Common mammal forearm / leg / flipper.

Vestigial Structures

•  Organs or structures that are reduced in size and seem to have little or no function. Vestigial structures are considered to be evidence of an organism’s evolutionary past

•  ex: Whale’s pelvic bone, blind salamander eye socket, our appendix, our wisdom teeth.

Amino Acid sequences.

•  Look at page 287 for an example,

•  Species descended from a recent common ancestor have fewer amino acid differences between their proteins than do species that have a common ancestor further back in time.

•  We can take amino acid sequence differences and graph them to create a phylogenic tree. A phylogenetic tree shows relationships and common ancestory using some trait (in this case, amino acid sequences.)

Embryology

•  All vertebrate embryos have similar structures.

•  All have a tail, buds that become limbs and pharyngeal pouches.

•  We lose the tail. Mammals, birds and reptiles lose the pharyngeal pouches…in fish and amphibians they become gills

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Co-evolution

•  Co-evolution occurs when 2 different species both evolve in reaction to each other.

•  2 great examples:

–  Plants and herbivores

–  Flowers and pollinators

–  ADAPTATION

•  Remember that each species has adaptations that help it fit perfectly into its specific niche (location and role)

•  Remember that individuals cannot adapt. A species adapts as helpful mutations assist some organisms in being more fit and those mutations are passed on

•  Biogeography – A study of the geographic distribution of organisms.

•  Convergent Evolution – organisms living in the same area evolve structures that are similar (analogous) in spite of their evolutionary ancestors being very dissimilar or unrelated.

•  Example of analogous structures:

–  butterfly and bird wing;

–  fusiform shape of dolphins, tuna,sharks, and penguins.

•  Forces in Evolution

•  Genetic Drift – a small population will exaggerate a difference resulting in speciation.

–  Founder’s effect

–  Bottleneck effect