Ruth Mace - Academia.edu (original) (raw)

Papers by Ruth Mace

Human culture changes over time and varies across space. Two main approaches to study cultural ev... more Human culture changes over time and varies across space. Two main approaches to study cultural evolution have developed in the last fifty years: human behavioural ecology and a suite of perspectives centred on the role of cultural transmission. The latter are often confusingly referred to with the name of the phenomenon they are trying to explain, ‘cultural evolution’. We argue that this is unhelpful and is generating confusion, including the claim that human behavioural ecology disregards cultural evolution. The aim of behavioural ecology is to explain human behaviours, and the vast majority of them are at least to some extent cultural. In addition, culture forms part of the ecology that determines the costs and benefits associated with adopting a behaviour. Thus, human behavioural ecologists have studied cultural evolution from the very beginning, even though they have not focussed on social learning. We explore three examples in detail: kinship systems, religious institutions, an...

Annals of Human Genetics, 2018

The genetic trait of lactase persistence (LP) evolved as an adaptation to milking pastoralism in ... more The genetic trait of lactase persistence (LP) evolved as an adaptation to milking pastoralism in the Old World and is a well-known example of positive natural selection in humans. However, the specific mechanisms conferring this selective advantage are unknown. To understand the relationship between milk drinking, LP, growth, reproduction, and survival, communities of the Coquimbo Region in Chile, with recent adoption of milking agropastoralism, were used as a model population. DNA samples and data on stature, reproduction, and diet were collected from 451 participants. Lactose tolerance tests were done on 41 of them. The European −13,910*T (rs4988235) was the only LP causative variant found, showing strong association (99.6%) with LP phenotype. Models of associations of inferred LP status and milk consumption, with fertility, mortality, height, and weight were adjusted with measures of ancestry and relatedness to control for population structure. Although we found no statistically significant effect of LP on fertility, a significant effect (P = 0.002) was observed of LP on body mass index (BMI) in males and of BMI on fertility (P = 0.003). These results fail to support a causal relationship between LP and fertility yet suggest the idea of a nutritional advantage of LP. Furthermore, the proportion of European ancestry around the genetic region of −13,910*T is significantly higher (P = 0.008) than the proportion of European ancestry genome-wide, providing evidence of recent positive selection since European-Amerindian admixture. This signature was absent in nonpastoralist Latin American populations, supporting the hypothesis of specific adaptation to milking agropastoralism in the Coquimbo communities. K E Y W O R D S Adaptation, body mass index, lactase persistence, Latin America, natural selection, pastoralism 1 INTRODUCTION Lactase, the enzyme responsible for the digestion of lactose in milk, is downregulated after weaning in most mammals, This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Evolutionary Human Sciences, 2021

Cultural diversity is disappearing quickly. Whilst a phylogenetic approach makes explicit the con... more Cultural diversity is disappearing quickly. Whilst a phylogenetic approach makes explicit the continuous extinction of cultures, and the generation of new ones, cultural evolutionary changes such as the rise of agriculture or more recently colonisation can cause periods of mass cultural extinction. At the current rate, 90% of languages will become extinct or moribund by the end of this century. Unlike biological extinction, cultural extinction does not necessarily involve genetic extinction or even deaths, but results from the disintegration of a social entity and discontinuation of culture-specific behaviours. Here we propose an analytical framework to examine the phenomenon of cultural extinction. When examined over millennia, extinctions of cultural traits or institutions can be studied in a phylogenetic comparative framework that incorporates archaeological data on ancestral states. Over decades or centuries, cultural extinction can be studied in a behavioural ecology framework to investigate how the fitness consequences of cultural behaviours and population dynamics shift individual behaviours away from the traditional norms. Frequency-dependent costs and benefits are key to understanding both the origin and the loss of cultural diversity. We review recent evolutionary studies that have informed cultural extinction processes and discuss avenues of future studies.

Behavioral Ecology, 2022

The term cultural evolution has become popular in the evolutionary human sciences, but it is ofte... more The term cultural evolution has become popular in the evolutionary human sciences, but it is often unclear what is meant by it. This is generating confusion and misconceptions that are hindering progress in the field. These include the claim that behavioral ecology disregards culture. We argue that these misunderstandings are caused by the unhelpful use of term cultural evolution to identify both a phenomenon—culture changing through time—and a theory to explain it—the potential role of cultural transmission biases in driving this change. We illustrate this point by considering recently published influential studies and opinion pieces. If we are to avoid confusion, the term cultural evolution is best reserved to identify the phenomenon of cultural change. This helps clarify that human behavioral ecologists do not disregard culture, but instead have studied its evolution from the very beginning. Different approaches to the study of human behavior can coexist and complement each other...

Behavioral Ecology

Why parents in some societies induce some of their sons to become religious celibates is an evolu... more Why parents in some societies induce some of their sons to become religious celibates is an evolutionary puzzle. Some have speculated that this might be associated with brother competition for family resources. However, the behavioral ecology of monks and the possible links with competition between brothers remain unexplored. Here, we use demographic data from Amdo Tibetan agropastoralists in western China to evaluate what factors determine the probability of becoming a monk and explore the possible association between wealth and having a monk brother. We found that boys with at least one older brother are more likely to become celibate monks. Patrilocal heads of household, who inherit parental property, are more likely to be first-born sons, whereas men who marry uxorilocally, that is they move to their wife’s household, are generally second- or later-born sons. Moreover, we find that men with at least one monk brother are wealthier than men who only have non-celibate brothers. Tog...

The growth of individual, north Kenyan, pastoralist families' herds of smallstock, given to them ... more The growth of individual, north Kenyan, pastoralist families' herds of smallstock, given to them in restocking schemes, is followed over several years. Very poor families given similar herds at the start of the project showed great variation in herd sizes by the end of the period analysed. There were highly significant between-year differences in mean herd growth, which appeared to be ultimately caused by climatic variation. But there were no significant between-family effects. That is to say, families that did worse than average in one year were no more likely to do worse than average in another year than was any other family. The extent to which families depended on income from sources other than their herd is clearly shown to decrease as herd size increases, but families with well over 100 goats were still dependent on some additional source of income for at least 50% of the time. It is concluded that although families are, in general, managing their herds to the best of their ability, unpredictable livestock mortality is inevitable and will lead to wide variation in household success. The factors causing this variation are largely unavoidable in the environment in which these pastoralists live. Its existence should therefore be accepted and taken into account in the planning and assessment of restocking schemes, and in any other interventions concerning pastoralists' herds.

The purpose of this research is found out the influence of knowledge, skill and attitude to midwi... more The purpose of this research is found out the influence of knowledge, skill and attitude to midwife professionalism and to seek which one among them that has significant influence on professionalism. This research uses quantitative method with inferential approach. Sample collection technique is random sampling with sample amount of 75 from 105 students. Data analysis method is parametric statistic analysis with regression-3 predictor as its technique analysis. It is evident that F count value (12,390) is bigger than F table value (3,350). Thus, this research had proven that there is significant influence from midwife knowledge ((X 1), midwife skill (X 2), midwife attitude (X 3) to midwife professionalism (Y). Summary of this research are 1) Knowledge, skill and midwife attitude act together in influencing midwife professionalism 2) Knowledge, skill, and midwife attitude have influence on midwife professionalism in partial. 3) Midwife knowledge gives more dominant influence to midwife professionalism compare to midwife skill and attitude.

12 Pastoralism and the evolution of lactase persistence CLARE HOLDEN AND RUTH MACE Introduction I... more 12 Pastoralism and the evolution of lactase persistence CLARE HOLDEN AND RUTH MACE Introduction In most parts of the world, the ... lactase-persistent adults are able to derive a nutritional benefit from lactose in milk, which is not available to non-persistent individuals. ...

Comparative primate socioecology, 2001

... 396 R. Mace & C. Holden EaWolof Sara l-terero Ambo Mbundu Amba Ndembu Ngala Kaonde 7 ... more ... 396 R. Mace & C. Holden EaWolof Sara l-terero Ambo Mbundu Amba Ndembu Ngala Kaonde 7 Nilotics Kunama Shona Ndau Venda ... C. Holden apply in the case of cattle pastoralism, as herds are in need of constant protection from theft (which women ... Sunderland, MA: Sinauer ...

Substitute parents: Alloparenting in human societies. …

The idea that humans are co-operative breeders has been around for several decades, but has only ... more The idea that humans are co-operative breeders has been around for several decades, but has only recently been subjected to empirical testing across disparate cultures. We have investigated this issue in a farming community in the Gambia, by analysing whether there is any ...

American Journal of Physical Anthropology, 1999

The following cultural variables were tested for their association with sexual dimorphism: sexual... more The following cultural variables were tested for their association with sexual dimorphism: sexual division of labor, type of subsistence (hunting and agriculture), and polygyny. The transmission of these traits among populations was investigated. All the traits were found to be associated with phylogeny, indicating that they are inherited from mother to daughter populations. A cross-cultural comparative method was used which controls for the statistical effects of similarity due to common ancestry (Galton's problem). Cross-cultural variation in sexual dimorphism in stature is negatively associated with women's contribution to subsistence. Women are taller, relative to men, in societies where women contribute more to food production. This may be because female nutritional status is better in these societies. No relationship was found between sexual dimorphism and other aspects of subsistence or polygyny. These results are discussed in relation to other studies of sexual dimorphism in modern and archaeological populations, and in relation to cross-cultural variation in sex-biased parental investment.

American Journal of Human Biology, 2012

American Journal of Human Biology, 2009

In earlier work in rural Gambia, we found that kin influence reproductive success: matrilineal ki... more In earlier work in rural Gambia, we found that kin influence reproductive success: matrilineal kin, especially mothers, maternal grandmothers and unmarried older sisters all helped to promote the survival and nutrition of young children; in contrast patrilineal kin, especially husband's mother, promoted fertility. These differing influences of maternal and paternal lineage are predicted on the basis of kin selection and sexual conflict theory, because the costs of reproduction fall more heavily on the mother than the father. These studies covered the period 1950-1975, when this population was essentially "natural fertility, natural mortality." It is not possible to tell whether these effects were due to kin influencing active reproductive decision-making, or due to indirect effects such as kin improving nutrition by helping. Since 1976, modern contraception has become available in this community. In an analysis of the behavioral ecology of the decision to start using modern contraception, we found that high parity for your age was a key determinant of the decision, as was village and calendar year. Here, we examine whether the presence or absence of kin and also whether the contraceptive status of kin influenced the decision to start using contraception. We find little evidence that kin directly influence contraceptive uptake, either by their presence/absence or as models for social learning. However, death of a first husband (i.e., widowhood) does accelerate contraceptive uptake. We discuss our results from an evolutionary demography perspective, in particular regarding theories of sexual conflict, biased cultural transmission, and social learning.

Agricultural Systems, 1989

We present a general model of a camel and small stock, nomadic pastoral system. The model address... more We present a general model of a camel and small stock, nomadic pastoral system. The model addresses the question o['how household wealth should he divided between camels and small stock in order to maximise the long term viabili O' of the household in an environment where rainfall is unpredictable. The modelling technique used is stochastic dynamic programming. The model shows that the optimal ratio o/'camels to small stock depends on total household wealth. In general, poor households should on O, invest in small stock. Once herd size is above a critical limit, the household should then invest most of its wealth in camels. This critical herd size depends, mainO', on the subsistence requirement of the household. Once investing in camels, the number of small stock kept depends mainO, on the variahilio' of small stock herd growth rate and on their price relative to camels. The importance qf changing strategy according to wealth is illustrated by comparing the long term survival chances of households following the optimal polio3' with households following two other simple strategies which do not depend on wealth. The strategy with the highest mean productivi O, of the three in the

Agricultural Systems, 1990

Most nomadic pastoralist groups keep more than one livestock species, and Mace & ... more Most nomadic pastoralist groups keep more than one livestock species, and Mace & Houston (1989) have shown, through modelling, how the appropriate mix of species can promote household survival chances in an unpredictable environment. Optimal herd compositions have been ...

Agricultural Systems, 1996

A model of household decision-making in dryland agropastoral systems is presented, This is used t... more A model of household decision-making in dryland agropastoral systems is presented, This is used to find the optimal combination of crops and livestock that a farmer will choose to keep, depending on household wealth, under the assumption that farmers act to minimize their long-term probability of destitution. The farmer can choose to plant a high-risk crop such as maize, a low-risk crop such as millet, and to keep goats or cattle. An interaction between these components is modelled, involving the use of cattle for draft power. It is shown that very poor farmers will choose to plant maize, whereas cattle are kept only if they are to be used for draft power, and only by the wealthier farmers.

Human culture changes over time and varies across space. Two main approaches to study cultural ev... more Human culture changes over time and varies across space. Two main approaches to study cultural evolution have developed in the last fifty years: human behavioural ecology and a suite of perspectives centred on the role of cultural transmission. The latter are often confusingly referred to with the name of the phenomenon they are trying to explain, ‘cultural evolution’. We argue that this is unhelpful and is generating confusion, including the claim that human behavioural ecology disregards cultural evolution. The aim of behavioural ecology is to explain human behaviours, and the vast majority of them are at least to some extent cultural. In addition, culture forms part of the ecology that determines the costs and benefits associated with adopting a behaviour. Thus, human behavioural ecologists have studied cultural evolution from the very beginning, even though they have not focussed on social learning. We explore three examples in detail: kinship systems, religious institutions, an...

Annals of Human Genetics, 2018

The genetic trait of lactase persistence (LP) evolved as an adaptation to milking pastoralism in ... more The genetic trait of lactase persistence (LP) evolved as an adaptation to milking pastoralism in the Old World and is a well-known example of positive natural selection in humans. However, the specific mechanisms conferring this selective advantage are unknown. To understand the relationship between milk drinking, LP, growth, reproduction, and survival, communities of the Coquimbo Region in Chile, with recent adoption of milking agropastoralism, were used as a model population. DNA samples and data on stature, reproduction, and diet were collected from 451 participants. Lactose tolerance tests were done on 41 of them. The European −13,910*T (rs4988235) was the only LP causative variant found, showing strong association (99.6%) with LP phenotype. Models of associations of inferred LP status and milk consumption, with fertility, mortality, height, and weight were adjusted with measures of ancestry and relatedness to control for population structure. Although we found no statistically significant effect of LP on fertility, a significant effect (P = 0.002) was observed of LP on body mass index (BMI) in males and of BMI on fertility (P = 0.003). These results fail to support a causal relationship between LP and fertility yet suggest the idea of a nutritional advantage of LP. Furthermore, the proportion of European ancestry around the genetic region of −13,910*T is significantly higher (P = 0.008) than the proportion of European ancestry genome-wide, providing evidence of recent positive selection since European-Amerindian admixture. This signature was absent in nonpastoralist Latin American populations, supporting the hypothesis of specific adaptation to milking agropastoralism in the Coquimbo communities. K E Y W O R D S Adaptation, body mass index, lactase persistence, Latin America, natural selection, pastoralism 1 INTRODUCTION Lactase, the enzyme responsible for the digestion of lactose in milk, is downregulated after weaning in most mammals, This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Evolutionary Human Sciences, 2021

Cultural diversity is disappearing quickly. Whilst a phylogenetic approach makes explicit the con... more Cultural diversity is disappearing quickly. Whilst a phylogenetic approach makes explicit the continuous extinction of cultures, and the generation of new ones, cultural evolutionary changes such as the rise of agriculture or more recently colonisation can cause periods of mass cultural extinction. At the current rate, 90% of languages will become extinct or moribund by the end of this century. Unlike biological extinction, cultural extinction does not necessarily involve genetic extinction or even deaths, but results from the disintegration of a social entity and discontinuation of culture-specific behaviours. Here we propose an analytical framework to examine the phenomenon of cultural extinction. When examined over millennia, extinctions of cultural traits or institutions can be studied in a phylogenetic comparative framework that incorporates archaeological data on ancestral states. Over decades or centuries, cultural extinction can be studied in a behavioural ecology framework to investigate how the fitness consequences of cultural behaviours and population dynamics shift individual behaviours away from the traditional norms. Frequency-dependent costs and benefits are key to understanding both the origin and the loss of cultural diversity. We review recent evolutionary studies that have informed cultural extinction processes and discuss avenues of future studies.

Behavioral Ecology, 2022

The term cultural evolution has become popular in the evolutionary human sciences, but it is ofte... more The term cultural evolution has become popular in the evolutionary human sciences, but it is often unclear what is meant by it. This is generating confusion and misconceptions that are hindering progress in the field. These include the claim that behavioral ecology disregards culture. We argue that these misunderstandings are caused by the unhelpful use of term cultural evolution to identify both a phenomenon—culture changing through time—and a theory to explain it—the potential role of cultural transmission biases in driving this change. We illustrate this point by considering recently published influential studies and opinion pieces. If we are to avoid confusion, the term cultural evolution is best reserved to identify the phenomenon of cultural change. This helps clarify that human behavioral ecologists do not disregard culture, but instead have studied its evolution from the very beginning. Different approaches to the study of human behavior can coexist and complement each other...

Behavioral Ecology

Why parents in some societies induce some of their sons to become religious celibates is an evolu... more Why parents in some societies induce some of their sons to become religious celibates is an evolutionary puzzle. Some have speculated that this might be associated with brother competition for family resources. However, the behavioral ecology of monks and the possible links with competition between brothers remain unexplored. Here, we use demographic data from Amdo Tibetan agropastoralists in western China to evaluate what factors determine the probability of becoming a monk and explore the possible association between wealth and having a monk brother. We found that boys with at least one older brother are more likely to become celibate monks. Patrilocal heads of household, who inherit parental property, are more likely to be first-born sons, whereas men who marry uxorilocally, that is they move to their wife’s household, are generally second- or later-born sons. Moreover, we find that men with at least one monk brother are wealthier than men who only have non-celibate brothers. Tog...

The growth of individual, north Kenyan, pastoralist families' herds of smallstock, given to them ... more The growth of individual, north Kenyan, pastoralist families' herds of smallstock, given to them in restocking schemes, is followed over several years. Very poor families given similar herds at the start of the project showed great variation in herd sizes by the end of the period analysed. There were highly significant between-year differences in mean herd growth, which appeared to be ultimately caused by climatic variation. But there were no significant between-family effects. That is to say, families that did worse than average in one year were no more likely to do worse than average in another year than was any other family. The extent to which families depended on income from sources other than their herd is clearly shown to decrease as herd size increases, but families with well over 100 goats were still dependent on some additional source of income for at least 50% of the time. It is concluded that although families are, in general, managing their herds to the best of their ability, unpredictable livestock mortality is inevitable and will lead to wide variation in household success. The factors causing this variation are largely unavoidable in the environment in which these pastoralists live. Its existence should therefore be accepted and taken into account in the planning and assessment of restocking schemes, and in any other interventions concerning pastoralists' herds.

The purpose of this research is found out the influence of knowledge, skill and attitude to midwi... more The purpose of this research is found out the influence of knowledge, skill and attitude to midwife professionalism and to seek which one among them that has significant influence on professionalism. This research uses quantitative method with inferential approach. Sample collection technique is random sampling with sample amount of 75 from 105 students. Data analysis method is parametric statistic analysis with regression-3 predictor as its technique analysis. It is evident that F count value (12,390) is bigger than F table value (3,350). Thus, this research had proven that there is significant influence from midwife knowledge ((X 1), midwife skill (X 2), midwife attitude (X 3) to midwife professionalism (Y). Summary of this research are 1) Knowledge, skill and midwife attitude act together in influencing midwife professionalism 2) Knowledge, skill, and midwife attitude have influence on midwife professionalism in partial. 3) Midwife knowledge gives more dominant influence to midwife professionalism compare to midwife skill and attitude.

12 Pastoralism and the evolution of lactase persistence CLARE HOLDEN AND RUTH MACE Introduction I... more 12 Pastoralism and the evolution of lactase persistence CLARE HOLDEN AND RUTH MACE Introduction In most parts of the world, the ... lactase-persistent adults are able to derive a nutritional benefit from lactose in milk, which is not available to non-persistent individuals. ...

Comparative primate socioecology, 2001

... 396 R. Mace & C. Holden EaWolof Sara l-terero Ambo Mbundu Amba Ndembu Ngala Kaonde 7 ... more ... 396 R. Mace & C. Holden EaWolof Sara l-terero Ambo Mbundu Amba Ndembu Ngala Kaonde 7 Nilotics Kunama Shona Ndau Venda ... C. Holden apply in the case of cattle pastoralism, as herds are in need of constant protection from theft (which women ... Sunderland, MA: Sinauer ...

Substitute parents: Alloparenting in human societies. …

The idea that humans are co-operative breeders has been around for several decades, but has only ... more The idea that humans are co-operative breeders has been around for several decades, but has only recently been subjected to empirical testing across disparate cultures. We have investigated this issue in a farming community in the Gambia, by analysing whether there is any ...

American Journal of Physical Anthropology, 1999

The following cultural variables were tested for their association with sexual dimorphism: sexual... more The following cultural variables were tested for their association with sexual dimorphism: sexual division of labor, type of subsistence (hunting and agriculture), and polygyny. The transmission of these traits among populations was investigated. All the traits were found to be associated with phylogeny, indicating that they are inherited from mother to daughter populations. A cross-cultural comparative method was used which controls for the statistical effects of similarity due to common ancestry (Galton's problem). Cross-cultural variation in sexual dimorphism in stature is negatively associated with women's contribution to subsistence. Women are taller, relative to men, in societies where women contribute more to food production. This may be because female nutritional status is better in these societies. No relationship was found between sexual dimorphism and other aspects of subsistence or polygyny. These results are discussed in relation to other studies of sexual dimorphism in modern and archaeological populations, and in relation to cross-cultural variation in sex-biased parental investment.

American Journal of Human Biology, 2012

American Journal of Human Biology, 2009

In earlier work in rural Gambia, we found that kin influence reproductive success: matrilineal ki... more In earlier work in rural Gambia, we found that kin influence reproductive success: matrilineal kin, especially mothers, maternal grandmothers and unmarried older sisters all helped to promote the survival and nutrition of young children; in contrast patrilineal kin, especially husband's mother, promoted fertility. These differing influences of maternal and paternal lineage are predicted on the basis of kin selection and sexual conflict theory, because the costs of reproduction fall more heavily on the mother than the father. These studies covered the period 1950-1975, when this population was essentially "natural fertility, natural mortality." It is not possible to tell whether these effects were due to kin influencing active reproductive decision-making, or due to indirect effects such as kin improving nutrition by helping. Since 1976, modern contraception has become available in this community. In an analysis of the behavioral ecology of the decision to start using modern contraception, we found that high parity for your age was a key determinant of the decision, as was village and calendar year. Here, we examine whether the presence or absence of kin and also whether the contraceptive status of kin influenced the decision to start using contraception. We find little evidence that kin directly influence contraceptive uptake, either by their presence/absence or as models for social learning. However, death of a first husband (i.e., widowhood) does accelerate contraceptive uptake. We discuss our results from an evolutionary demography perspective, in particular regarding theories of sexual conflict, biased cultural transmission, and social learning.

Agricultural Systems, 1989

We present a general model of a camel and small stock, nomadic pastoral system. The model address... more We present a general model of a camel and small stock, nomadic pastoral system. The model addresses the question o['how household wealth should he divided between camels and small stock in order to maximise the long term viabili O' of the household in an environment where rainfall is unpredictable. The modelling technique used is stochastic dynamic programming. The model shows that the optimal ratio o/'camels to small stock depends on total household wealth. In general, poor households should on O, invest in small stock. Once herd size is above a critical limit, the household should then invest most of its wealth in camels. This critical herd size depends, mainO', on the subsistence requirement of the household. Once investing in camels, the number of small stock kept depends mainO, on the variahilio' of small stock herd growth rate and on their price relative to camels. The importance qf changing strategy according to wealth is illustrated by comparing the long term survival chances of households following the optimal polio3' with households following two other simple strategies which do not depend on wealth. The strategy with the highest mean productivi O, of the three in the

Agricultural Systems, 1990

Most nomadic pastoralist groups keep more than one livestock species, and Mace & ... more Most nomadic pastoralist groups keep more than one livestock species, and Mace & Houston (1989) have shown, through modelling, how the appropriate mix of species can promote household survival chances in an unpredictable environment. Optimal herd compositions have been ...

Agricultural Systems, 1996

A model of household decision-making in dryland agropastoral systems is presented, This is used t... more A model of household decision-making in dryland agropastoral systems is presented, This is used to find the optimal combination of crops and livestock that a farmer will choose to keep, depending on household wealth, under the assumption that farmers act to minimize their long-term probability of destitution. The farmer can choose to plant a high-risk crop such as maize, a low-risk crop such as millet, and to keep goats or cattle. An interaction between these components is modelled, involving the use of cattle for draft power. It is shown that very poor farmers will choose to plant maize, whereas cattle are kept only if they are to be used for draft power, and only by the wealthier farmers.