• To be able to discuss how differences in survival influences an organism’s ability to pass its DNA on to future generations.
• To be able to discuss how differences in reproductive success and the ability to attract a mate influences an organism’s ability to pass its DNA on to future generations.

Evolution is a change in the gene frequency in a population from one generation to the next. Natural selection is the mechanism behind evolution. Evolution can occur at 2 levels. Microevolution refers to the small genetic changes that affect one characteristic of a population such as coloration. Macroevolution describes the large scale, long-term dramatic genetic changes that result in a new species. Species refers to a group of closely related organisms that are able to breed with one another and produce fertile offspring Speciation is the formation of 2 species from 1 as the result of divergent natural selection in response to changes in the environmental conditions.

Before understanding what evolution is it may be best to understand what it is not. Table 1 lists many of the misconceptions about evolution. Probably the most common misconception is that evolution results from the survival of the strongest. In reality evolution occurs because of the survival of the fittest which refers to reproductive success. If evolution was based on the survival of the strongest we would all be elephants.

The Theory of Natural Selection describes the process by which beneficial genes are reproduced in succeeding generations more than other genes. Natural selection involves several factors.

1. All populations of organisms show variation

Some variations are more useful than others. Variation in a gene pool can be caused by: mutation, immigration (individuals entering the population), emigration (individuals leaving the population) and from natural selection.

The trait must allow the individuals to exploit the niche better than other individuals of the population and it must be heritable. Non-genetic traits can not be passed on to offspring.

2. In nature all organisms produce more offspring than can survive

3. Accordingly there is a shortage of resources; which results in a struggle for survival.

4. Some individuals of a species have a better chance for survival than others.

5. These individuals will leave more offspring

6. As time passes each generation is subjected to the same processes of natural selection. The percentage of individuals showing favorable variations will increase and those with unfavorable variation will decrease

Genetic survival, the ability to pass on DNA, is depended on an individual being able to find the resources needed for survival that include being able to get food and water, find nesting sites, and be able to defend a territory. It is also important not to be eaten. Genetic survival also depends on the ability to reproduce which will include surviving until it can mate, finding a mate, and having offspring that live until they reproduce. Succeeding in being able to find resources and reproduce depends upon being able to overcome selective pressures. Selective pressures are caused by environmental factors which cause some individuals with certain traits to survive and reproduce more than the rest of the population. These pressures can be caused by abiotic or non-living factors and biotic or living factors in the environment.

The major biotic factor is competition which occurs when more than one organism strives for limited resources. There is always competition for resources and mates. Competition, predation, the availability of food, water, and nesting sites, along with other environmental conditions such as temperature, and pH can create limiting factors that affect the size and range of a population.

Competition is based on differential survival, reproductive rates and mate selection.

A range of genetically different individuals is likely to consist of individuals that have genes that will make their survival more difficult or less difficult. Individuals that have characteristics that make their survival more difficult are more likely to die early and not pass their genes on. This does not mean that they will not have offspring it just means that they are not as likely to have as many offspring as other individuals. Where as individuals that have characteristics that make their survival less difficult are likely to live longer and pass their successful genes on.

Some individuals are better able to physically produce more offspring because of physiologic factors such as fertility and the lifespan of the adult. An individual that lives longer either because of their physical health or because they can get more resources can have more offspring. Reproductive success is also going to depend on the individual’s ability to protect its offspring. Protecting the offspring depends on providing a sturdy nest or shelter, being able to hide and protect the offspring from predators and supply the offspring with good nutrition.

Some individuals can attract a mate better than other individuals. The ability to attract a mate may depend on a number of physical and behavioral factors. Physical factors can include body side or outward characteristics such as bright feathers or coloration. Aggressiveness may indicate an individual that can protect a territory and protect the offspring thus those individuals may be more attractive. Other behaviors may include courtship behaviors or the ability to build a nest and choose a good territory.

1. Avoiding Toxic Plants

The ability to find food that is not poisonous is essential to the survival of an individual and their offspring. Plants that taste bad are often poisonous so being sensitive to bitter taste improves an individual’s survival and they have more offspring.

1. Individuals will be given a piece of PTC paper.

   The ability to taste PTC paper is genetic. Some individuals find that it is bitter and other individuals find that it has no taste at all.

2. Students will taste the paper and record if they are a taster or a non-taster on the Data Record.

C. Record how many offspring survive on the Data Record.

Analysis of results:

Tasters: Individuals that can discriminate the bitter taste will be less likely to feed poisonous food to their offspring thus they will have more offspring that can survive. They will have 10 offspring.

Non-Tasters: Individuals that cannot discriminate the bitter taste will be more likely to feed poisonous food to their offspring thus they will have fewer offspring that can survive. They will have 5 offspring.

 

2. Spotting Danger and Locating Food

In order to survive an individual must be able to spot danger from predators before they are either eaten or their offspring are eaten so visual acuity is critical. The number of offspring an individual has will thus be related to their eyesight

1. To test eyesight the instructor will write a 4-5 letter word in letters about ¾-1 inch high on an index card.
2. The students will line up 15 feet away and attempt to determine what the word is when the instructor holds it up.
3. The students should write what they thought the word is without discussing it with other students.
4. Afterwards the instructor will tell the class what the word is.
5. Record how many offspring survive on the Data Record.

Analysis of results:

Correctly identify word: They will be able to protect their offspring because they have excellent eyesight and can spot danger from far away. They will have 10 offspring.

Correctly identify 2-3 letters: They can not protect all of their offspring because they have poor eyesight. They will have 5 offspring.

Identify fewer than 2 letters: They have very poor eyesight and were probably eaten before they could reproduce. They have 0 offspring.

3. Health and Nutrition

Individuals with poor nutritional habits are less likely to be healthy, conceive, and if offspring are born they will not be able to successfully rear them.

1. To test nutritional habits each student should record what they had for breakfast that morning on the Data Record.
2. Using the basic food groups of cereal, milk products, fruit, vegetables and meat determine how many food groups are represented by breakfast.
3. Record how many offspring survive on the Data Record

Analysis of results

3 or more major food groups: These are healthy individuals that feed their offspring well. They will have 10 offspring.

1-2 major food groups: This diet cannot sustain many offspring. They will have 5 offspring.

0 food groups or only coffee or soda: This is a very unhealthy diet that can not successfully support the raising of offspring. They will have 0 offspring.

Physical factors such as fertility and the lifespan of the adult determine how many offspring they have and thus their ‘fitness.’ Not all individuals are equal so it is critical that mates be chosen to capitalize on these physical factors.

1. Each student is handed a playing card.
2. Prior to the beginning of the lab the instructor will make a list of "pairings" and the resultant offspring. (i.e. pairings of hearts, or face cards or specific numbers will result in 0, 1, 2, 3 offspring, etc)
3. Students will pair off and present their cards to the instructor to be told how many offspring they have.
4. Pairings should be repeated through 10 "breeding seasons". Students can try to improve their reproductive success by finding new mates or by remaining monogamous.
5. Record the offspring for each "breeding season" in the Data Record

Some individuals can attract a mate better than other individuals. In many species the male finds a territory and prepares a nest and displays it to arriving females. The female than determines which mate has the best nest.

1. The class should be divided into ‘males’ that will build nests and ‘females’ that will inspect and accept or reject a nest.
2. The ‘males’ be given plastic bowls for nests and nest material.
3. The ‘males’ should select 5 items from the nest material for their nests. They can exchange part or all of the nests each breeding season.
4. The ‘females’ are given a checklist to analyze the nests. They are not to show the checklists to the ‘males’
5. The checklists should have 8 or 9 items on it. The males can either gain points or lose points based on the items that were picked from the nesting materials. A sample point system can be:

   0 to 2 points 0 offspring

   3 points 1 offspring

   4 points 2 offspring

   5+points 3 offspring

6. For the ‘female’ it is a first come first serve basis. ‘Females’ can either chose an unpaired mate or double up on a nest but the second ‘female’ can not produce as many offspring so automatically subtract 1 for her total.
7. Once chosen the ‘female’ tells the ‘male’ how many offspring they had.
8. In between round the ‘females’ migrate to the hallway and the ‘males’ can rebuild nests.
9. Repeat for 10 rounds or 10 breeding seasons.

The maximum number of offspring is 30. Survey the class and fill in the following chart.

The maximum number of offspring is 30. Survey the class and fill in the following chart.

Assuming that the ‘females’ had more control and direct knowledge of what a successful nest was survey the ‘males’ to determine how successful they were.