Behavioral development in animals undergoing domestication

Abstract

The process of domestication involves adaptation, usually to a captive environment. Domestication is attained by some combination of genetic changes occurring over generations and developmental mechanisms (e.g., physical maturation, learning) triggered by recurring environmental events or management practices in captivity that influence specific biological traits. The transition from free-living to captive status is often accompanied by changes in availability and/or accessibility of shelter, space, food and water, and by changes in predation and the social environment. These changes set the stage for the development of the domestic phenotype. Behavioral development in animals undergoing domestication is characterized by changes in the quantitative rather than qualitative nature of responses. The hypothesized loss of certain behavior patterns under domestication can usually be explained by the heightening of response thresholds. Increases in response frequency accompanying domestication can often be explained by atypical rates of exposure to certain forms of perceptual and locomotor stimulation. Genetic changes influencing the development of the domestic phenotype result from inbreeding, genetic drift, artificial selection, natural selection in captivity, and relaxed selection. Experiential contributions to the domestic phenotype include the presence or absence of key stimuli, changes in intraspecific aggressive interactions and interactions with humans. Man's role as a buffer between the animal and its environment is also believed to have an important effect on the development of the domestic phenotype. The domestication process has frequently reduced the sensitivity of animals to changes in their environment, perhaps the single-most important change accompanying domestication. It has also resulted in modified rates of behavioral and physical development. Interest in breeding animals in captivity for release in nature has flourished in recent decades. The capacity of domestic animals to survive and reproduce in nature may depend on the extent to which the gene pool of the population has been altered during the domestication process and flexibility in behavioral development. “Natural” gene pools should be protected when breeding wild animals in captivity for the purpose of reestablishing free-living natural populations. In some cases, captive-reared animals must be conditioned to live in nature prior to their release.

Introduction

Animal domestication is best viewed as a process, more specifically, the process by which captive animals adapt to man and the environment he provides. Since domestication implies change, it is expected that the phenotype of the domesticated animal will differ from the phenotype of its wild counterparts. Adaptation to the captive environment is achieved through genetic changes occurring over generations, and environmental stimulation and experiences during an animal's lifetime (Price, 1984). In this sense, domestication can be viewed as both an evolutionary process and a developmental phenomenon.

This review constitutes a summary of the literature dealing with the effects of domestication on the behavior of captive animals. The emphasis in this article is placed on environmentally induced changes in the development of behavior accompanying the domestication of farm, laboratory and companion animals. (See Price, 1998, Darwin, 1868, for a companion review paper focusing on genetic contributions to the domestic phenotype). After defining domestication, the reader is introduced to some of the changes in the animal's environment associated with the transition from nature to captivity. Changes in the quantity and quality of space and shelter available to captive animals, changes in behaviors associated with feeding and drinking, the reduction of predation and changes in the social environment are discussed with respect to their role in behavioral modification and adaptation to the captive environment. While artificial selection and natural selection in captivity facilitate adaptation to the captive environment over generations, the unique experiences of individuals foster adaptation within their lifetime. Environmentally induced changes in the behavior of domestic animals are reflected in the role of key stimuli, changes in intraspecific aggression, interactions with humans, and responsiveness to environmental change as well as in rates of development including neoteny. The review concludes with a short treatment of feralization and concerns associated with rearing animals in captivity for release in nature.