The History of a Meal

The History of a Meal

OBJECTIVE(S):

Upon completion of this activity, students should be able to:

1.Analyze a food to determine the plants it contains.

2.Name the place of origin of 15 food crops.

3.Define plant breeding, domesticated plants, crop evolution, natural and artificial selection, genetic variation.

4.With a partner, outline a procedure that early plant breeders might have used to domesticate a wild plant species.

5.Write a paragraph explaining why it is important to on serve wild plants, from a plant breeder's point of view.

MATERIALS AND/OR EQUIPMENT:

●Nonmeat food products brought from home by students

●World map showing continents, countries, bodies of water

●Crop origin cards (included)

●World crop map with some countries and regions labeled (included)

TIME REQUIRED FOR ACTIVITY:

Three class periods

BACKGROUND MATERIAL:

(Adapted from "Crop Origins and Plant Improvement", by Sonja Williams, College of Agriculture, University of Illinois.)

Imagine that the entire history of humans of Earth has been compressed into a single day. It is now midnight, the end of that day. At what time do you suppose people began farming? They began just 14 minutes ago at about 11:46 p.m.!

Archaeologists think that people have been farming for less than 10,000 years. This is a very short time compared to the million years that people are thought to have been on Earth.

Before people cultivated plants, they got their food by a way of life called, "hunting and gathering." In the 20th century, we depend on agriculture for most of our food. Very few people anywhere in the world survive by hunting and gathering today, but until 7000 or 8000 B.C. all people lived this way.

Agriculture is defined as "the science or art of cultivating the soil, producing crops, and raising livestock, and ... preparation of these products for ... use." While agriculturists depend on domesticated (tame) plants or animals, hunters and gatherers depend on stands of wild plants or herds of wild animals. People who live by hunting and gathering must move from place to place as their food resources become depleted.

Many events had to occur over a very long period of time for people to change from hunter-gatherers to farmers and city dwellers. Early hunter-gatherers found natural populations (stands) of wild grain and harvested these stands by hand. You can understand how difficult this may have been if you imagine gathering tiny seeds of a wild plant such as foxtail for your food. Fortunately, hunter-gatherers had many kinds of plants and animals from which to choose.

Modern archaeologists and agronomists have discovered evidence that very productive varieties of wild wheat and other grains existed in prehistoric times. These grain plants grew in scattered natural stands in various areas of the Near East, especially in Turkey, Iran, and Iraq.

Those plants may have had other traits (phenotypes) that made them appealing to the early hunter-gatherers. They may have had larger kernels, different colors, or may have grown taller than today's common wild varieties. Some may have had seed heads that didn't "shatter," but held on to their mature seeds. Groups of hunter-gatherers settled in villages near large stands of productive wild grains.

Because many seed heads did shatter easily, many of the seeds produced in wild stands would be planted naturally each year as they were collected by hunter-gatherers. (In much the same way today, corn seeds germinate in fields and along roadsides from grain dropped by combines during harvest.) People in villages began to count on the yearly production of "naturally planted" grains in the areas surrounding their villages.

The next step in the development of farming in the Near East was actual domestication of wild plants. Domestication included deliberately collecting, saving, and planting seeds, not just setting up camp near a natural stand of wild plants.

When people realized they could collect seeds and plant them the following season, they may have noticed that some seeds developed into more vigorous and healthier plants. At the end of the growing season, they saved seeds from these plants to sow the next year. In this way, early people became involved in plant selection and improvement.

Plants can be improved by selection. Plants possessing desirable phenotypes (traits) are selected or saved. Desired traits might include higher yield, disease resistance, better taste, production of fruit or seeds at a certain time of year, and many other characteristics. Seeds from selected plants usually develop into a high (or predicable) percentage of offspring with traits similar to the parents.

Although prehistoric people had no idea how traits were passed from one generation to the next, they made use of their observations to select plants with characteristics they wanted to preserve. It has only been in our century that plant breeders have begun to understand that a blueprint or plan for organisms' traits exists in every living cell in the form of a chemical called DNA. DNA is usually contained in structures called genes, which are segments of larger structures called chromosomes. The DNA carried in the chromosomes is passed from one generation of organisms to their offspring in observable and understandable ways. The study of biological properties that are transmitted through DNA from one generation to the next is called genetics.

At a later stage in the history of plant domestication, plant growers learned they could sometimes use two different plants as parents and get offspring with a combination of the two parents' traits. Repro-duction which involves male and female reproductive cells (eggs and sperm) is called sexual reproduction. The process of selective mating of plants is called plant breeding. If plants with a different DNA code are mated, the process is called hybridization. The offspring (the F1 generation) are called hybrid plants.

Hybridization worked best between similar plants because the plants often had very similar types and numbers of chromosomes. Popula-tions of similar plants which can be hybridized belong to the same species. Occasionally, plants that are not similar to each other can mate and produce live offspring. However, many times offsprings of crosses between species with different types and numbers of chromosomes are sterile and cannot produce offspring by mating or sexual reproduction.

Through a painstaking process of selection, planting, hybridization, and further selection of plants with desired traits, early farmers developed most of the cultivars or varieties we know today. Wheat and many other crops were domesticated in the Near East. Plant domestications occurred in their parts of the world, too. China, Southeast Asia, Mexico, and South America are all regions where important crops were first domesticated. In all these place, farmers were discovering wild plants, selecting, and breeding them to increase the populations of plants with desired characteristics.

This process can be described as crop evolution. Evolution is the change in the frequency of characteristics of a population over time. The process of crop evolution is dependent on variation in traits of plants, selection of individuals with certain traits, and reproduction of the selected individuals.

Crop evolution, as described above, occurs as a result of artificial selection, in which people select the plants that will reproduce. However, in the natural environment sometimes members of a plant population are able to survive and reproduce while other members don't survive and therefore do not reproduce. This process (which does not require that people do the selecting) is called natural selection.

Natural selection has also played a role in crop evolution. An example of the role of natural selection in crop evolution is the development of species or varieties of plants suited to certain climates. Because of differences in climate in different parts of the world, crops from specific regions may have greater tolerance for cold, drought, heat, or flooding than crops from other regions. The climate, not people, has acted to select the individuals most capable of reproducing in that environment.

Because early plant breeders had little understanding of genetics, development of new or improved varieties of plants took a long time. Crop evolution and improvement occurred mostly through a process of trial and error. But modern plant breeders use an understanding of genetics to speed up the process of plant improvement.

Plant improvement requires more than just a knowledge of genetics. It requires genetic variation, so that breeders can choose different traits to breed into crops. The variation comes from different individuals of the same species of plants, or it may come from traits contained in different species.

Today, only about 150 species of plants are cultivated as crop plants. Another 1,000 species are not cultivated, but are important to people for wood, fiber, medicine, and food. Worldwide, there are over 350,000 species of plants. Some of these 350,000 species can provide much variation for future crop development. The wild plants of today may become the crops of tomorrow.

PROCEDURE:

(Adapted from "Crop Origins and Plant Improvement", by Sonja Williams, College of Agriculture, University of Illinois.)

Imagine that there are no grocery stores. Imagine that you can't have a garden because there are no seeds to buy. Where would you get your food?

You would probably learn to harvest wild plants, just as hunter-gatherer cultures still do in remote parts of the world. This is a difficult way to get your goods and becomes even more difficult when there are many people in a small area of and. Cultivated plants can be grown in much greater densities and can feed greater populations.

It is important to remember that all food corps began as wild plants. Through the long process of domestication described in the Background section of this unit, you learned some of the steps in domesticating or selecting wild plants. Archaeologists and agronomists specializing in crop evolution have worked like patient detectives to uncover evidence of the origins of crop plants.

This activity investigates the history of some of the food plants that people in our society take for granted. You will see how long ago people first domesticated food plants and will get an idea of how far food plants have spread from their original homes.

Class Preparation

Display nonmeat food products brought by students from home for this activity. Suitable foods are fruits, vegetables or processed products. Make sure students bring the container or box for processed foods such as breakfast cereals, cookies, or macaroni so that plant products contained in the foods can be identified.

Copy and cut out a set of crop origin cards for each five students if each students does not have a workbook.

Copy one map sheet per student if each student does not have a workbook.

(Read the Background section and the Introduction to Activity before class.)

1.Look at all the foods that were brought to class by other students. List 15 different plants that are contained in these food items. You may have to do some detective work in the library to discover the plants that make up certain foods.

1.9.

2.10.

3.11.

4.12.

5.13.

6.14.

7.15.

8.

2.Use the crop origin cards to find the original home of each of the 15 food plants on your crop map. Write the name of a crop plant near its place of origin. Since exact places of origin are not known for most plants, you need only find the general area where the crop is thought to have originated. (You may have to look at a more detailed world map to find a specific country. You can enter the information on your crop map.)

If the cards don't contain a description of one or more of the food plants, you can use the library to research the origin of a crop plant. The Learning More resources found in the reference section gives some suggested books to help you research crop origins.

3.Work with a partner to outline the steps early farmers could have used to develop crop plants and improve their characteristics. You can look for these steps in the background reading. It might help to think about a plant that is part of the food product you brought to class. The first step will be the wild version of the plant; use as many steps as you need.

STEP 1:Find a group of wild plants.

______

STEP 2:

______

______

STEP 3:

______

STEP 4:

______

______

4.Write a paragraph to describe why it is important to preserve wild plants, from a plant breeder's point of view.

Crop Origin Cards

Crop: Wheat
Scientific Name:
Triticum aestivum
Place of origin/history of cultivation: Wheat was first cultivated in the Near East (Turkey, Iran, Iraq), North Africa, and Afghanistan. Fossil grains 9,000 to 10,000 years old have been discovered. / Crop: Sugarcane
Scientific Name:
Saccharam officinarum, a grass
Place of origin/history of cultivation: Sugarcane is thought to be from New Guinea or Java in Southeast Asia. It is known to have been grown for thousands of years.
Crop: Corn
Scientific Name:
Zea mays
Place of origin/history of cultivation: Field corn looks very different from existing wild corn plants, so its history is not clear. Scientists think it originated in Mexico and South America. A wild relative of corn, teosinte, has been found in Mexico. Teosinte has the same number of chromosomes as modern corn, and both annual and perennial forms exist. It was cultivated as long ago as 5000 B.C. / Crop: Green pepper