Origin of Species

Introduction to Evolution

Review:

1. How does the DNA of an organism determine the structure and function of the proteins that the organism produces? The nitrogen bases are in a certain sequence

2. Why do individuals of a particular species differ? Genetically unique

3. How is variation introduced into a species? Meiosis (sexual reproduction)

A Little Bit of Geology:

What is a fossil? A trace of a long-dead organism

Where are fossils found? Often in the layers of sedimentary rock

How do scientists determine the “relative age” of fossils? Law of Superposition- successive layers of rock or soil are deposited on top of one another; Half-life using Carbon 14 Dating; Mold-Imprint- imprint of an organism’s shape in sedimentary rock…..cast-mold filled with minerals (rock-like)

Theories of Evolution: Before we begin, a few vocabulary words need to be introduced:

Species- a group of organisms of a single type that are capable of producing fertile offspring in the natural environment

Population- all the members of a species that live in the same area and make up a breeding group

1. The term evolution refers to an orderly succession of changes. Biological evolution is the change of populations of organisms over generations.

2. Early scientists noticed that new life-forms appeared to be modifications of fossil forms found in the same geological area. This strongly implied that a natural modification process was at work.

3. The French scientist Jean Baptiste de Lamarck (1744-1829) was one of the first to propose a unifying hypothesis of species modification. In other words, Lamarck was the first to develop a theory of evolution.

Lamarck’s Theory: similar species descended from a common ancestor or living species were descended from a similar extinct species

What is an acquired? Give an example of an acquired trait. A trait that is not determined by genes

Can an acquired characteristic change the genotype of an organism? No

Can we pass “acquired traits” onto our offspring? No Is Larmack’s theory valid No

4. In 1831, a young man by the name of Charles Darwin boarded the H.M.S. Beagle as a naturalist. The Beagle was charted for a five-year mapping and collecting expedition to South America and the South Pacific.

5. Before Darwin departed on his voyage, he was convinced, like most people of the time, that species were un-related. At the same time, he was discovering many fossils himself and was struck by the fact that many fossils resembled living forms.

6. Of all the areas visited by Darwin, it was the Galapagos Islands that had the most profound influence on his thinking. In particular, the small finches found on the islands caught his attention. While all of the small birds were finches, they had differentiated (evolved) into 14 species with remarkably different beaks.

What was significant about the structure of the beaks? They were specialized for a particular food source. The similarities implied that they shared a common ancestor.

Based on Darwin’s experience and observations in the Galapagos Islands, what theories could be developed to explain the presence of different finch species? The offspring of the original finches had adapted to different environments and food sources.

7. In the mid-1800’s, both Charles Darwin and Alfred Wallace independently proposed the hypothesis that species were modified through a process called natural selection.

Darwin’s Theory:

1. Descent with modification- the newer forms appearing in the fossil record are modified descendents of older species (few common ancestors).

2. Modification by natural selection- some organisms have traits that make them better able to cope with their environment. Organisms that have a greater number of these traits reproduce more successfully

What is meant by the term “fitness”? A single organism’s genetic contribution to the next generation

While Darwin and Wallace announced their hypotheses at the same time, Darwin’s name became more associated with evolution after his book The Origin of Species was published in 1859.

8. Darwin was influenced by two men while developing his theory.

Charles Lyell (geologist)- his book, Principles of Geology, caused Darwin’s interest in the study of geology and allowed him to consider the possibility that the modification of environments might be a slow process requiring long periods of time.

Thomas Malthus (clergyman)- his thesis left Darwin to believe that the environment limits the growth of populations by increasing the rate of death or decreasing the rate of reproduction or both

Review: