EVOLUTION AND ADAPTIONS

Unit Overview
In this unit, we will examine some frequently asked questions concerning evolution in an attempt to clarify and focus specifically what the Theory of Evolution is. This unit is not an attempt to influence an individual’s right to believe any theory about creationism but simply to reveal what the evolutionary theory of creation professes. We will also examine the Theory of Adaptation, which shares some similar concepts with evolution.

Unit Directions
Read the material and answer the test questions at the conclusion of the unit. To further understand some of the areas go on line to the WGBH site or search PBS television for Evolution. These sites will enable you to click on various film clips to provide support material for each area of the article.

The Basics

1. What is evolution?

Biological evolution refers to the cumulative changes that occur in a population over time. These changes are produced at the genetic level as organisms' genes mutate and/or recombine in different ways during reproduction and are passed on to future generations. Sometimes, individuals inherit new characteristics that give them a survival and reproductive advantage in their local environments; these characteristics tend to increase in frequency in the population, while those that are disadvantageous decrease in frequency. This process of differential survival and reproduction is known as natural selection. Non-genetic changes that occur during an organism's life span, such as increases in muscle mass due to exercise and diet, cannot be passed on to the next generation and are not examples of evolution.

2. Isn't evolution just a theory that remains unproven?

In science, a theory is a rigorously tested statement of general principles that explains observable and recorded aspects of the world. A scientific theory, therefore, describes a higher level of understanding that ties "facts" together. A scientific theory stands until proven wrong, but it is never proven correct. The Darwinian theory of evolution has withstood the test of time and thousands of scientific experiments; nothing has disproved it since Darwin first proposed it more than 150 years ago. Indeed, many scientific advances, in a range of scientific disciplines including physics, geology, chemistry, and molecular biology, have supported, refined, and expanded evolutionary theory far beyond anything Darwin could have imagined.

Introduction to Charles Darwin's Theory of Evolution (00:54)

3. Are all species related?

Yes. Just as the tree of life illustrates, all organisms, both living and extinct, are related. Every branch of the tree represents a species, and every fork separating one species from another represents the common ancestor shared by these species. While the tree's countless forks and far-reaching branches clearly show that relatedness among species varies greatly, it is also easy to see that every pair of species share a common ancestor from some point in evolutionary history. For example, scientists estimate that the common ancestor shared by humans and chimpanzees lived some five to eight million years ago. Humans and bacteria obviously share a much more distant common ancestor, but our relationship to these single-celled organisms is no less real. Indeed, DNA analyses show that although humans share far more genetic material with our fellow primates than we do with single-celled organisms, we still have more than 200 genes in common with bacteria.

It is important to realize that describing organisms as relatives does not mean that one of those organisms is an ancestor of the other or, for that matter, that any living species is the ancestor of any other living species. A person may be related to blood relatives, such as cousins, aunts, and uncles, because he shares with them one or more common ancestors, such as a grandparent, or great-grandparent. However, those cousins, aunts, and uncles are not her ancestors. In the same way, humans and other living primates are related, but none of these living relatives is a human ancestor.

For additional information on the tree of life, click on the following PDF File: Tree of Life PDF File

4. What is a species?

Members of one species do not normally interbreed with members of other species in nature. Sometimes, members of different species, such as lions and tigers, can interbreed if kept together in captivity. But in nature, geographic isolation and differences in behavior, such as choice of habitat, keep these sorts of closely related animal species apart. Similarly, closely related species of plants can sometimes be hybridized by horticulturists, but these hybrids are rarely found in nature. A species, then, is defined by science as a group of interbreeding or potentially interbreeding populations that is reproductively isolated from other such groups.

5. What do genes have to do with evolution?

Genes are the portions of an organism's DNA that carry the code responsible for building that organism in a very specific way. Genes — and, thus, the traits they code for — are passed from parent to offspring. From generation to generation, well-understood molecular mechanisms reshuffle, duplicate, and alter genes in a way that produces genetic variation. This variation is the raw material for evolution.

6. What role does sex play in evolution?

Sexual reproduction allows an organism to combine half of its genes with half of another individual's genes, which means new combinations of genes are produced every generation. In addition, when eggs and sperm are produced, genetic material is shuffled and recombined in ways that produce new combinations of genes. Sexual reproduction, therefore, increases genetic variation, which increases the raw material on which natural selection operates. Genetic variation within a species, also known as genetic diversity, increases a species' opportunity for change over successive generations.

7. Is evolution a random process?

Evolution is not a random process. The genetic variation on which natural selection acts may occur randomly, but natural selection itself is not random at all. The survival and reproductive success of an individual is directly related to the ways its inherited traits function in the context of its local environment. Whether or not an individual survives and reproduces depends on whether it has genes that produce traits that are well adapted to its environment.

The Proliferation of Species (02:33)

8. Are evolution and "survival of the fittest" the same thing?

Evolution and "survival of the fittest" is not the same thing. Evolution refers to the cumulative changes in a population or species through time. "Survival of the fittest" is a popular term that refers to the process of natural selection, a mechanism that drives evolutionary change. Natural selection works by giving individuals who are better adapted to a given set of environmental conditions an advantage over those that are not as well adapted. Survival of the fittest usually makes one think of the biggest, strongest, or smartest individuals being the winners, but in a biological sense, evolutionary fitness refers to the ability to survive and reproduce in a particular environment. Popular interpretations of "survival of the fittest" typically ignore the importance of both reproduction and cooperation. To survive but not pass on one's genes to the next generation is to be biologically unfit. And many organisms are the "fittest" because they cooperate with other organisms, rather than competing with them.

9. How does natural selection work?

In the process of natural selection, individuals in a population who are well-adapted to a particular set of environmental conditions have an advantage over those who are not so well adapted. The advantage comes in the form of survival and reproductive success. For example, those individuals who are better able to find and use a food resource will, on average, live longer and produce more offspring than those who are less successful at finding food. Inherited traits that increase individuals' fitness are then passed to their offspring, thus giving the offspring the same advantage.

10. How do organisms evolve?

Individual organisms don't evolve. Populations evolve. Because individuals in a population vary, some in the population are better able to survive and reproduce given a particular set of environmental conditions. These individuals generally survive and produce more offspring, thus passing their advantageous traits on to the next generation. Over time, the population changes.

11. Does evolution prove there is no God?

No. Many people, from evolutionary biologists to important religious figures like Pope John Paul II, contend that the time-tested theory of evolution does not refute the presence of God. They acknowledge that evolution is the description of a process that governs the development of life on Earth. Like other scientific theories, including Copernican theory, atomic theory, and the germ theory of disease, evolution deals only with objects, events, and processes in the material world. Science has nothing to say one way or the other about the existence of God or about people's spiritual beliefs.

Adaptations

Adaptation is a theory that shares similar ideas with evolution, but it is less controversial. An adaptation is an adjustment to the environment. Any characteristic that helps an animal to survive is considered an adaptation. Evolution focuses on all the changes that happen through time. Adaptation looks at the changes happening in one species during a time period or major event. There are many different types of adaptations, they can be behavioral, physical, and even the type of diet they have can be considered an adaptation. Again Darwin was a major part in discovering these changes in animals. He was studying in the Galapagos Island from 1831 – 1836. He noticed that on each island the finches’ beaks were different sizes and shapes. The beaks ranged from large round beak to tiny pointed beaks. Looking at the picture below, why do you think they are different?

First think, “What is the beak mostly used for?” That would be communication and eating food. So Darwin observed that food that was readily available on each island was different, although the islands were quite similar.

Finches with larger beaks would survive better on an island with seeds better than on an island with many cacti. On all the islands there was not just one type of finch. All beaks sizes were on each island, however, natural selection had its effect on each island.

This is on example of adaptation concerning diet. If an animal is an herbivore, carnivore, or an omnivore that is also considered a diet adaptation. Food is a basic need of all living things, along with water, shelter, space or carrying capacity, and waste disposal. As mentioned many times, any characteristic that helps and organism obtain their basic needs is an adaptation.

Coloring

There are many different types of physical adaptations; they can be anything to do with any parts of the body or coloring. Coloring is a major one. Animals that use coloring to blend into their surroundings are camouflage. A white rabbit would not survive in a wooded area because it would be easily seen. A white rabbit would have a higher survival rate in an area that has snow for most of the year.

A fantastic example of animals adapting to their environment and changing colors is the peppered moths. In England, the white moth with black spots was pretty common. The moths called home, trees with light colored bark and mosses.

Once the Industrial Revolution began in England less and less of these moths were seen. These moths were not just disappearing, they were changing color. Darwin’s words of survival of the fittest were being seen. Now that soot from all the new industries was covering trees, white moths were more easily seen by their predators; therefore darker moths had a better chance of surviving. The number of black peppered moths began to increase. This change can now be seen in reverse. Industries have standards that keep the air cleaner, so the white barked trees are staying white. So the peppered moths are returning to their original color.

Warning color is another way color is used for defense. The most commonly known animal that uses warning color is the poison dart frog. The bright colors tell predators they are poisonous. Many animals steal coloring or patterns from other animals. Mimicry is when an animal looks, sounds, or acts like another animal to fool other animals into thinking it is dangerous or poisonous. The Owl Butterfly pictured below has the same coloring and eye patterns as the owl. From a distance in a tree it would be difficult to tell that it is not an owl.

Behavior

Animals use certain behaviors to help them to survive. These are common behaviors that you many not of thought of as adaptations. Schooling or herding is when animals travel and stay in large numbers. When traveling in groups there are more eyes, ears, and bodies to detect and fend off danger. Being nocturnal is a behavioral adaptation. To be awake during the night, animals need special eyes to see clearly. The majority of nocturnal animals have large eyes with large pupils. This allows the eyes to take in more light, which makes the darkness clearer.

Hibernation is when an animal will go into a deep sleep, usually during the colder months. Animals go into hibernation to conserve energy because their food source is scarce during a certain time of year. Right before hibernation animals eat large amounts of food. That food builds up fat which is where their energy is stored. Once in hibernation, the animal’s heart rate is slowed and its body temperature is dropped. As they sleep, their body uses the energy that is in the fat. As a result they will lose most of the weight they gained before hibernation. Migration is when animal travel to another area. This is mostly seen in the colder months. Once it gets cold, food supply is low, so some animals have to travel to a warmer climate. Some animals travel thousands of miles to reach their destination.

Now answer questions 1 through 25.