Domestication of plants and origin of agriculture in Mesoamerica
Archaeological research carried out in different parts of the world allows us to identify regions where the oldest remains of cultivated plants are found, which are considered as probable centres of origin of agriculture.
Among the regions with the oldest remains, the area known as the Fertile Crescent in the Middle East and Mesoamerica, especially in the central part of Mexico, have been recorded so far. It is estimated that in the first region, agriculture may have begun to be used about 11 000 years ago, while in Mesoamerica this may have occurred 9000 or 10 000 years ago.
Other equally important regions are the Andean region of Peru, Ecuador and Chile; equatorial Africa; the Mediterranean region; Southeast Asia; and some regions of northern China.
It is known that the adoption of agriculture was a gradual process and apparently emerged independently in each of the sites mentioned. However, there are still many questions about how and why agriculture began to be adopted as the main form of human subsistence.
Some authors believe that the scarcity of resources obtained through harvesting, due to climate change or human population growth, may have been a factor in stimulating their increasingly widespread use. Other authors consider that its adoption should rather be seen as a stage in a process of technological development.
Harvesting, agriculture, and domestication
Today, Mexico's rural indigenous population bases its subsistence on agriculture, mainly on corn, beans, and chili, its staple foods. However, about 15% of the elements of their diet are still obtained from hunting and gathering a wide variety of wild animals and plants. Agriculture and plant collection have had a long history of coexistence in Mesoamerica.
Different archeological investigations in sites of human occupation in prehistory show that approximately 8500 years ago, hunting and gathering were predominant activities of Mesoamerican men and that the cultivation of plants was still incipient. However, over time, agriculture became an increasingly important activity, and shortly before the Spanish Conquest about 80% of the indigenous subsistence depended on cultivated plants.
If one compares the resource collection processes of some indigenous groups in Mexico, the differences between forms of agricultural management and collection can be very tenuous. For this reason, in order to discuss the origin of agriculture, it is necessary to characterize the distinctive features of this process and distinguish it from other ways of obtaining resources.
The main difference between plant collection and agriculture is that while the first activity involves a direct harvest of natural products, the second involves a productive process through which nature is transformed and the availability of resources controlled.
Agricultural management generally includes some form of manipulation of the environment that aims to create an artificial environment in which man seeks to control variables such as nutrient quantity, humidity, light, temperature, competitors, predators and other ecological factors in order to ensure the availability of plant resources. The process in which the environment is manipulated and plants are propagated in an artificially produced environment can generally be considered a crop.
Hernández-X. considers that in order to cultivate a wild species it is necessary to modify the genetic scheme resulting from processes of natural selection to another scheme adapted to conditions managed by man and to other anthropocentric purposes.
This observation emphasizes that agricultural management also includes mechanisms for human manipulation of plant genotypes. The manipulation of genotypes is the cultural activity that allows man to adapt biological diversity to the needs of human society and to artificial management conditions. This manipulation is carried out mainly through a particular form of selection: artificial selection.
It was Darwin who first described the way artificial selection operates in plants and animals, by favoring desirable individuals and eliminating undesirable ones. In plants, this process can have spectacular results in relatively short times with the sowing and ex situ planting of successive generations. However, when other forms of in situ management are analysed, neither the selective processes nor their results are as evident as in ex situ sowing.
Artificial selection and other artificial evolutionary forces are aimed at designing and creating organisms that satisfy human requirements and can grow in man-made environments. The evolutionary process resulting from human manipulation of plant and animal genotypes is precisely the domestication process. Therefore, agriculture is a productive process in which both the cultivation and domestication of plants are involved.
Origin of agriculture in Mesoamerica, archaeological evidence
The cultural area known as Mesoamerica, which encompasses approximately the southern half of Mexico and part of Central America, has been considered one of the most important centers of plant domestication in the world. A possible explanation for this may be the coexistence of an extraordinary plant diversity and a long cultural history.
Thus, in Mexico alone, there are about 30,000 species of flowering plants and more than 50 indigenous ethnic groups. Mexico's indigenous peoples currently use and manage more than 5,000 plant species, with which they maintain different forms of interaction. For this reason, Mesoamerica can be considered a living laboratory for the domestication of plants. And everything seems to indicate that it has been for thousands of years.
Archaeological investigations of Mesoamerican prehistory conducted by MacNeish in the Sierra de Tamaulipas and Tehuacán Valley, Puebla, and by Flannery in Guilá Naquitz, Oaxaca, have revealed important information about the early stages of plant domestication and the origin of agriculture in Mesoamerica.
In the Tehuacán Valley, Smith and MacNeish agree that the first evidence of morphological changes in plants, determined by human manipulation, is found in the chupandía (Cyrtocarpa procera), the avocado (Persea americana) and the chile (Capsicum annuum) in strata of approximately 8000 years ago.
In Guilá Naquitz, Flannery found the oldest evidence of domestication in guajes (Lagenaria siceraria) and pumpkins (Cucúrbita pepo) in strata from about 9000 years ago. According to these authors, in both sites the cultivation of corn may have occurred up to two thousand years after the plants mentioned.
Although there is not enough evidence, MacNeish considers that because avocado and chili are not native to the Tehuacán Valley, the ancient specimens found there could be cultivated individuals and that, therefore, in that region the cultivation could have started about 8,000 years ago.
This author considers that there were possibly two types of agriculture in the Tehuacán Valley, one of them called barranca horticulture, which consisted of planting plants, such as pumpkins, in the barrancas near the caves inhabited by prehistoric men. The other type of incipient agriculture is called hydro-vegetable, and consisted of domesticated individuals, for example avocado or chili, were planted next to the springs or on the beaches of the Salado River, where they were irrigated throughout the year.
There is a third possible type of incipient crop in the Tehuacán Valley, for which there is also insufficient evidence, and which was considered by Smith. The characteristics of this type of crop are deduced from the following ideas proposed by Smith:
1) Agriculture, in any of its forms, implies favouring useful plants to the detriment of non-useful ones. The primary objective of the first farmers, then, was to promote the abundance of certain desirable species among the local flora.
2) The first forms of cultivation used by the people of the Tehuacán area involved only the removal of some undesirable plants in small patches of land, in order to create a favorable habitat for some desirable plants, which were planted either from their vegetative parts (stakes or tillers) or from their seeds.
3) When the Indians cleared space for planting, most species of useful plants were not removed. Mesquite and other legumes, chupandilla, nopales and other edible cacti, as well as many other species were left standing. The growers planted the species they wanted to harvest among these plants, which grew very successfully. Then, the natural vegetation was never completely removed, and after such a plot was abandoned, they could eventually return to it.
Based on these ideas, Smith considered that the first cultures of Tehuacán were probably the magueyes (Agave spp.) and nopales (Opuntia spp.) since these plants propagate vegetatively and, in addition, there is archaeological evidence that they were regular elements in the human diet.
From our point of view, this third type of incipient agriculture could be called dryland silviculture, since men probably favored the growth of useful plants such as legumes, nopales, cacti, fruit trees, etc., in dry environments, in a manner similar to that proposed by MacNeish in the barranca horticulture model.
In summary, archaeological studies of prehistory in Mesoamerica suggest that the cultivation and domestication of important crops such as corn and beans were preceded by experiences of domestication of other plants. These studies do not allow to clarify if there were forms of manipulation of plants prior to the first signs of domesticated plants. It is not possible to conclude what the first forms of cultivation were like either. Ethnobotanical information on the current management of some species may contribute to the interpretation of archaeological information.
Current management of plants by Mesoamerican indigenous peoples
Currently, domestication processes are actively carried out in Mesoamerica. These processes include plants that already have an advanced degree of domestication, that is, they depend to a large extent on man for survival and reproduction. But, in addition, Mesoamerican peoples also domesticate Arvensian and wild plants with little or no degree of domestication.
The former are plants that grow in man-made habitats but do not depend on man for survival and reproduction, while the latter grow naturally outside man-made habitats and cannot easily invade them. Domestication processes may include different species, but also wild, arvensian and domesticated populations of the same species.
Ethnobotanical studies have revealed that in Mesoamerica there is a wide spectrum of forms of interaction between men and plants. However, it is possible to distinguish two main forms of management: in situ and ex situ.
In situ management includes interactions that take place in the same spaces occupied by arvense and wild plant populations. At this level, men can take products of nature without significant disturbance, such as in some forms of collection, but they can also consciously or unconsciously alter the phenotypic or genotypic structure of plant populations in order to improve their utilitarian qualities or to increase the number of some desirable species. The main forms of in situ management are:
1. Harvesting. It basically consists of taking the useful plants or their parts directly from the natural populations. Most of the wild and arvensian useful plants reported in ethnobotanical studies are collected.
2. Tolerance. This form of management includes practices aimed at maintaining, within man-made environments, the useful plants that existed before the environments were transformed. Thus, in the indigenous rural areas of Mexico it is very common to observe that during the weeding of the milpas, people tolerate different species of edible annual arvense plants or quelites.
Examples of this form of management can be seen in quintoniles (Amaranthus hybridus), verdolagas (Portulaca olerácea) and green tomatoes (Physalis philadelphica) in many places in Mexico. In Guerrero Mountain, the same phenomenon is observed in the Alaches (Anoda cristatá) and in the Chipiles (Crotalaria pumita).
This same form of management is also observed among perennial species. For example, in the Tehuacán Valley and in the Balsas River basin it is very common for people to tolerate mezquites (Prosopis laevigata); guamúchiles (Pithecellobium dulce) and guajes colorados (Leucaena esculentá) as well as magueyes (Agave spp.); "nopales" (Opuntia spp.); "pitayas" (Stenocereus spp.) and other edible cacti.
3. Promotion or induction. This type of management consists of different strategies aimed at increasing the population density of useful plants in their natural habitats. It includes the sowing of seeds or the intentional propagation of vegetative structures in the same places occupied by populations of wild or arvensian plants. An example of this form of management is the one practiced by the Mixtecs of the Montaña de Guerrero to increase the amount of palms of the Brahea dulcís species.
This palm, which is a very important resource for making hats and petates that are commercialized by people, has a vegetative reproduction system by means of stolons that have the particularity of being resistant to fire. In some areas with favourable environmental conditions for the palm, the Mixtecs deliberately set fires to remove shrubs, herbs and tree seedlings in order to eliminate competitors and promote palm growth. A similar principle is used to encourage the growth of some pastures in order to increase the amount of fodder for livestock.
In the Tehuacán Valley, popolocas vegetatively propagate some species of useful cacti in natural plant communities. From branches, the pitayas (Stenocereus stellatus, S. pruinosus and S. marginatus) propagate; the chichipe (Polaskia chichipe) and the chende (Polaskia chende), as well as the baboso (Pachycereus hollianus), and from branch shoots the garambullo (Myrtillocactus geometrizans) and the chiotillo (Escontria chiotilla).
In many parts of Mexico, it is common for indigenous peoples not only to tolerate but even to intentionally propagate seeds of desirable arvensian plants within the fields in order to increase their population density.
Examples of this form of management can be seen in the Montaña de Guerrero with green tomatoes, quintoniles, alaches and chipiles. Mixtecos induce an increase in the availability of these plants during the storm for self-consumption. During the dry season, farmers with irrigated land are even able to market their products due to the scarcity of these plants during this period.
4. Protection. This form of management consists of special care to arvense and wild plants that the peasants carry out in order to ensure and expand their production. This care includes the eradication of competitors and protection against predators, fertilization, pruning, protection against frost, etc.. Robert Bye described an example of this form of management among the Tarahumara, who eliminate competitors from wild onions in their natural populations.
In Guerrero Mountain there are also examples of this form of management with the red guaje, as well as with green tomatoes and snake tomatoes, which are arvensian forms of tomatoes (Lycopersicon esculentum). In the first case, Mixtec farmers prune some preferred trees and occasionally also fumigate them to protect them against compuchyde pests. In the case of green tomatoes and Arvensian tomatoes, the Mixtecs fertilize, fumigate and protect against frost these plants that play a very important role in their diet.
On the other hand, ex situ management includes interactions that take place outside natural populations, in habitats created and controlled by man. These forms of management are commonly used with domesticated plants, but also with wild plants and arvenses. There are two main forms of ex situ management:
1. Transplant. It consists in the transplantation of complete individuals taken from natural populations. Examples of this form of management can be observed in Montaña de Guerrero with the mezcalero maguey (Agave cupreata), and a wild guava known locally as guayaba tlahuanca (Psidium guajava). E
In the first case, the maguey seedlings are taken to the milpas in order to form soil tension borders and to eventually use the products of this plant (edible flowers and leaves, as well as stems for mezcal production).
In the case of the Tlahuanca guava, the offspring of wild trees are transplanted to the family gardens. In the Tehuacán Valley similar examples can be observed with several species of magueyes pulqueros and mezcaleros, as well as with the garambullo.
2.Sowing and planting. This form of management includes the ex situ propagation of sexual and vegetative reproductive structures. Guajes (Leucoma spp.), avocados, and various species of fruit trees, such as guavas, nanches (Byrsonima crassifolia), white zapote (Casimiroa edulis), and plums (Spondias mombin) are some examples of wild trees propagated by seed in the mixed orchards of Montaña de Guerrero.
On the other hand, plums, chupandillo, nopales, pitayas (Stenocereus spp.), colorines (Erythrina spp.) and copales (Bursera spp.) are examples of wild trees whose vegetative reproductive structures (stems and branches) are very frequently planted in orchards and other agricultural systems both in the Balsas river basin and in the Tehuacán Valley.
Among the herbaceous species, in Montaña de Guerrero, the transplant of onions (Allium glandulosum) and friars (Euphorbia graminea) from their wild populations to family gardens can be observed. It can also be observed the cultivation of arvense species such as alaches, chipiles, mustard (Brassica campestris) and quintonil. All these species are grown on irrigated land, especially in the dry season, and then marketed.
Artificial selection processes
There are still not enough studies to demonstrate and evaluate the effects of artificial selection processes on the forms of management described above. However, there are important observations to suggest that these processes are occurring. Thus, for example, many plant species obtained through harvesting, mainly annual plants, are collected without special preferences.
With others, however, especially perennials, collectors commonly distinguish individuals who are different in traits related to both their quality and their resources. For example, among edible plants, people distinguish flavors, textures, sizes, colors, the presence of toxic substances, and so on.
From such a variety of options, collectors choose the "best" plants according to their cultural values, and use them. For example, in the Montaña de Guerrero, the Mixtecos distinguish sweet and bitter forms of guamúchil (Pithecellobium dulce) and collect the sweets. A similar situation is found with the red guajes (Leucaena esculenta).
The Mixtecs distinguish three varieties: 1) the Basque guajes, which are toxic; 2) the bitter guajes, which have bitter seeds and can only be eaten after roasting, and 3) the sweet guajes, whose seeds are still edible raw. The farmers selectively collect the sweet guajes. Bitter guages are also harvested, but only when sweets are scarce.
Among the herbaceous arvenses, a certain selection can also be observed during the tolerance practiced in weeding. The case of alaches and chipiles can be commented.
In each of these species the Mixtecos distinguish two variants: 1) "male" variants, which present narrow and pubescent leaves, with high fiber content and no palatable; and 2) "female" variants with wide, non-pubescent leaves, with less fiber content and pleasant flavor and texture. Farmers prefer to collect and consume the "female" variants of these plants. It could be expected that, due to harvesting, the population density of "female" plants would decrease and over time the "male" forms would predominate.
However, this does not happen, because during the harvest the Mixtecs only cut the young branches without destroying the plant. In practice, this form of harvesting is a form of pruning. In addition, during weeding, the farmers try to eliminate the "male" forms.
A similar process of selective tolerance can be observed in other species of wild edible plants. It occurs, for example, with "guamúchiles": bitter variants are usually eliminated when a field is opened or when firewood is cut. The same applies to bitter, cimarronas or sour variants of guavas and nanches.
In the case of colored guavas, Mixtec farmers prefer sweet variants and sometimes also some individuals of the bitter variant. But generally they eliminate bitter individuals and above all the toxic ones of Basque. In a study carried out in Montaña de Guerrero, we compared the frequency of favorable phenotypes in wild and cultivated populations, as well as in a population where selective tolerance has probably acted for several centuries.
We found a significantly higher frequency of favorable individuals in the tolerated population compared to the wild population. This suggests that selective action during tolerance may affect the phenotypic frequencies of the populations, and probably also the genotypic frequencies.
In summary, during some forms of in situ management of wild landscapes or arvenses, man is able to raise the population density of some useful plant species. This process by itself does not necessarily change the genetic structure of populations. However, in some cases, it appears that artificial selection may be acting in a similar way to ex situ cultivation. This suggests that in situ domestication of plants is a possible process.
The favoring of species and variants of these species that are suitable for humans is easy to visualize in plants with vegetative propagation such as magueys and some cacti. In these cases, men simply take reproductive structures of the forms they are interested in and propagate them. However, in species that present only sexual reproduction, the issue is not so trivial.
In this case, choosing fruits or seeds in the desired form may not be enough to ensure replication. This depends on the type of crossbreeding system involved. Thus, in a species where self-fertilization predominates, replication of the desired phenotype from harvested seeds may be direct. Whereas in plants in which crossing is predominant or in which crossing is forced, the sowing of harvested seeds does not guarantee the replication of the desired phenotype, according to the Mendelian principle of segregation.
The length of the life cycle can further complicate the selection process. Thus, recognizing and accepting or eliminating a variant form of a species is relatively quick in annual species, while the process can be very slow in perennial species with a long life cycle. In this respect, Smith's opinion on the domestication of avocado, one of the first crops in Mesoamerica, is interesting.
Smith believes that because it takes about seven years for an avocado seedling to produce, and the tree can continue to produce after seventy years or more, the selection period prior to its effective domestication by large cotyledons must have been extensive.
An in situ domestication model is attractive for analyzing the case of colored guajes (Leucaena esculenta subsp. esculenta) mentioned above. Guajes are perennial plants with cross-fertilization and, in them, an artificial selection pattern that occurs generation after generation could be a very long process. In this case, it would be more feasible to increase the number of desired phenotypes by leaving them standing in their natural populations than by cultivating them elsewhere.
Hypothetical models of the origin of agriculture
There are two main hypothetical models that have been proposed to explain how agriculture emerged and how it developed. One of them is the seminiculture model, which seeks to explain the origin of the cultivation of seed-propagated plants. This model has been based mainly on case studies of annual herbaceous plants such as the main cereals (wheat, oats, rice, maize, etc.) and legumes (beans, lentils, chickpeas, etc.).
In general, the scheme of this hypothetical model suggests that wild forms of domesticated plants first invaded areas disturbed by man, where they evolved as arvensian plants, and were eventually cultivated.
In this model, domestication is considered as a consequence of cultivation (and although it is not specified, it is generally referred to as a crop that we characterize in this article as ex situ). Authors like Harían consider that domestication is a process of natural evolution that results from selective pressures associated with harvesting and sowing.
The starting point is to consider that mutant plants that are favorable to man generally present a very low adaptation and are not capable of surviving in natural conditions. Therefore, the only way to ensure the survival of these plants is by establishing them, growing them and reproducing them in man-made controlled environments.
The second hypothetical model is that of vegeculture, which focuses on understanding the origin of the cultivation and domestication of vegetatively propagated plants. This model is based on the study of plants such as yams (Dioscorea spp.), yucca (Manihot esculenta), potato (Solanum tuberosum), vine (Vitis vinifera), etc. Harían believes that the ease with which these plants are propagated and domesticated could be an argument to support the idea that tropical vegeculture is older than seed farming.
This author suggests that the cultivation of these vegetatively propagated plants originated from the collection of vegetative structures, which were easily planted, harvested and replanted, practicing artificial selection every cycle. Under this model, therefore, ex situ cultivation is also a condition to domesticate the plants.
Although these two models have been widely developed for several decades, they do not satisfactorily explain the origin of the domestication of many plants, such as, for example, that of perennial plants with a cross-breeding system. For these plants, as noted above, an in situ domestication model is more attractive for explaining the origin of their domestication.
This model is based on considering the management of wild vegetation and the development of artificial selection practices in the same places where useful plants are naturally found. For this reason, a third model that considers in situ management and selection is necessary. From our point of view, this hypothetical model could be called the forestry model, alluding to the management of the wild.
The in situ domestication process could be even older than the assumption in the vegeculture hypothesis. The main assumption of a forestry hypothetical model is that agriculture is the result of a long history of in situ management of natural vegetation. In addition, it is more feasible to increase the number of desired phenotypes by selective tolerance, promotion or induction, and in situ protection of such phenotypes than by cultivating them ex situ.
With this selective action and the elimination of undesirable phenotypes, the frequency of crossing between desirable phenotypes could also be increased, thereby increasing the availability of desirable products in plant populations and communities, as well as an advantageous increase in the frequency of favourable phenotypes in the progeny. After a process like the one suggested here, the cycles of cultivation and selection of these plants would be more successful.
This hypothetical model of artificial selection in situ suggests that domestication may have been a feasible process in cultivation forms such as those described by Smith in the Tehuacán Valley and which we have here called dryland forestry. This model reinforces the hypothesis that agriculture is the result of a long technological history developed by man to manage both environments and plant genotypes.
This story undoubtedly began with the collection of plants, which apparently became more systematic as human knowledge of plants and environments increased and collection tools and techniques were developed.
The collection could be followed by forms of manipulation of forests and jungles in situ. The first stages of a process like this could have been an indirect modification of the genotypic structure of the populations, determined by forms of disturbance of the natural vegetation. Such disturbances can change the natural interrelationships between plants and their competitors, predators and possibly pollinators and dispersers, as well as other ecological factors.
This is a result of simplifying the structure of plant communities and increasing the population density of some species. In other words, intentional disturbances and other forms of natural vegetation management may have led to changes in natural selection pressures.
It is important to note that the new environments created after such disturbances are man-made environments, modified to meet human requirements, and that plants began to evolve within these intentionally man-made environments. For that reason, this stage could be called domestication of the environment.
A stage of artificial selection carried out also in situ on particular phenotypes of some species may have continued later. And finally, this stage could have been continued by forms of cultivation and ex situ artificial selection.
With the emergence and development of ex situ agricultural management, domestication greatly increased its potentials because the sequences of cultivation and selection, generation after generation, allowed man to intensify the manipulation of generations of plants. That is, in the ex situ agricultural management phase, human manipulations of genotypes are more evident.
Domestication and genetic resources
Mexico is a country exceptionally rich in plant and animal species, and it is also a country exceptionally rich in cultures. These cultures have managed to generate a vast technological experience over thousands of years with which they have been able to use and manage between 5,000 and 7,000 plant and animal species.
This broad spectrum of proven useful species and many more that could still be incorporated in the list, constitute an immense reservoir of resources for national development. In each of these useful species there is a particular set of characteristics that make them an option for directly resolving this or that human subsistence requirement or as a raw material for industry.
Even more impressive is perhaps the variability that can be found within each of these species, and that has also been used and managed differently by Mesoamerican cultures. Thus, as an example, in a study on pitayas or xoconochtles (Stenocereus stellatus), it can be observed that the popolocas, the mixtecos and the nahuas of the Tehuacán Valley and the Mixteca Baja, recognize and classify the variability of this species based on the traits of five characters of the fruits.
The characteristics and traits are as follows: (1) color, distinguishing red, pink, green, yellow, orange and purple varieties; (2) flavor, distinguishing sweet and sour varieties; (3) size, distinguishing small and large varieties; (4) shell, thick or thin; (5) thorny and non-spiny fruits. A combination of the traits of only these five characteristics makes possible the existence of 144 possible variants, each with a cultural meaning and a particular utilitarian role.
Thus, for example, people consider as the best fruits for direct consumption those of greater size, green color, sweet flavor, thin skin and not thorny. However, those of sour taste are preferred for the elaboration of drinks and jams; those of thorny fruits are more resistant to the attacks of the predators, the varieties of thick shell are more resistant to the rottenness and therefore they resist more the long days of transport, etc. All this great biological variety and technological experience exists for only one species.
In the 5 000 to 7 000 species and in their intraspecific variability there is a wide range of concrete and potential options to solve problems of feeding, health, construction, clothing, etc. Many of these species are not only unknown to the majority of the country's population, but are even destroyed on a daily basis along with the destruction of natural habitats.
One of the most urgent challenges for science and for contemporary society is the search for ways of sustainable development that will improve the quality of human life without destroying nature. In Mexico, this search must begin by considering its immense biological and cultural wealth. The formulation of any strategy for sustainable management of natural resources must not only take into account the need to conserve such an important heritage, but must also consider that this reservoir of diversity constitutes a fundamental point of support for the development of productive and cultural potential.
In order to do so, it is necessary to know each one of the resources, evaluate their potentialities, design conservation strategies for the species and their intraspecific variability, carry out technological development programs based on these resources and produce them on a larger scale. The experience of Mesoamerican domestics in the use and management of these resources constitutes an important step forward in the knowledge and use of the country's biological diversity. Therefore, one of the main tasks of ethnobiology is to rescue, for the entire society, the immense culture disseminated in the regions and towns of Mexico.
Source: Casas, Alejandro, and Caballero, Javier. 1995. Domestication of plants and origin of agriculture in Mesoamerica. Sciences, no. 40, October-December, pp. 36-45. [Online].