Wednesday, Oct. 11 - Genetics -Darwin and Evolution

Key Terms

Ancestry – The lineage or bloodline of descendants.

Cladograms – Diagrams that show the relationships of organisms.

Evolution – Change in living organisms over long periods of time.


Charles Dawin and Evolution

In 1859, Charles Darwin published “On the Origin of Species,” which proposed the theory that all forms of life developed gradually from different, usually simpler, parent organisms. He proposed that weaker (less adaptable) members of the population died without reproducing and that the strongest members of the population survived, reproduced and passed on those traits to the next generation.

Darwin also believed that everything that ever lived on Earth descended from a single, primitive organism and that evolution is responsible for all of the changes and diversity of species. This is called the Theory of Universal Common Ancestry.

Basically UCA says a caterpillar, a dog and a human all came from one ancestor. This was hard for people to believe because there was no real way to test Darwin’s theory. Also, religious beliefs (think Adam and Eve) made people reluctant to accept Darwin’s theories. To many people at the time, what Darwin was proposing was sacrilegious.

However, scientists have developed a test to see how related all the species on earth are. In general this test supports the idea of one common organism. They don’t know what it looks like, but they believe it was a simple, one-celled organism that lived in water.

In general, scientists say there are three major domains of life:

Eukarya – Humans, animals, plants, yeast





Cladistics is the method for studying the evolutionary relationships of organisms. Organisms are organized into clades (groups) that share the same evolutionary history. So the species in one clad have more in common with each other than they do with another clad. Cladograms are diagrams that show the relationship between species and track where traits diverge over time.

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