Chapter 6.1

Ideas About Evolution

Early Models of Evolution

  A species is a group of organisms that share similar characteristics and can produce fertile offspring. Evolution – changes in inherited characteristics over time.

Hypothesis of Acquired Characteristics

   Jean Baptiste de Lamarck said that characteristics or traits developed during a parent organism’s lifetime are inherited by offspring. He called these traits acquired traits. For example – he would say a body builder would acquire big muscles over their life and pass big muscles onto their children.

Scientists found no support for this idea so it was rejected.

Darwin’s Model of Evolution

 In 1831 Charles Darwin went on journey to observe plants and animals in South America. At the Galapagos Islands he found a great variety of plants and animals.

Darwin’s Observations

  Darwin observed 13 different species of finches. They were all similar except for body size, beak shape, and eating habits. From his observations he said that because of the competition for food that over time what started as one type of finch changed into 13 different species.

Natural Selection

 Natural selection – organisms with traits best suited to their environment are more likely to survive and reproduce. The traits that made them better suited are passed on.

Principles of Natural Selection

     1. Organisms produce more offspring than can survive.

2. Differences, or variation, occur among different individuals or species.

3. Some variations are passed to offspring.

4. Some variations are helpful. Individuals with helpful variations survive and reproduce better than those without these variations.

5. Over time, the offspring of individuals with helpful variations make up more of a population and eventually may become a separate species.

Variation and Adaptation

   Variation is an inherited trait that makes an individual different from other members of its species. Variation occurs from mutations, there are small variations or large variations.

An adaptations is any variation that makes an organism better suited to its environment. These can be changes in color, shape, behavior, or chemical makeup.

Changes in the Sources of Genes

   Genetic makeup of a species may change its appearance. Many environmental factors may bring about changes. Also when members of a population move in or out of an area it brings new genes in.

Geographic Isolation

  Sometimes a small number of individuals may become isolated from the rest of a population.

Since there isn’t as much variation, and gene mutations may occur the individuals may become very different from the original population they were a part of.

Gradualism

  Gradualism – the idea that evolution is a slow, ongoing process, where one species changes to a new species. This is caused by a series of mutations and variations.

Punctuated Equilibrium

 Punctuated Equilibrium is the idea that rapid evolution happens when a few genes mutate the appearance of a new species in a short amount of time.