Douglas S. Massey - Spheres of Influence: The Social Ecology of Racial and Class Inequality

The characteristics and behavior of all living organisms arise from a complex interaction between genes and the environment. This gene-environment interaction occurs not only within the genome of any species across historical time, but also within the lifetime of any particular organism. Among species, random mutations inevitably occur in the process of DNA replication and over time regularly introduce changes into its genome. These genetic changes may increase, decrease, or have no effect on an organism's ability to survive and reproduce. Those changes that enhance the odds of survival and reproduction are likely to be passed on and be retained in the genome. Those that reduce survival and reproduction are not passed on and over time disappear. Mutations that have no effect on survival or reproduction remain, though generally at lower frequencies.

This interaction between genes and the environment constitutes the core mechanism of evolution and has been recognized since the time of Charles Darwin (1859). The realization that genes interact with the environment within the lifetimes of individual organisms is much more recent. For many years, scientists had a rather static view of genetic inheritance, in which specific genes were passed on by parents and duly inherited and expressed by their progeny, irrespective of environmental conditions. Genes were invariably revealed biologically and the principal debate was over which was more importantgenes or the environmentin accounting for observed traits and behaviors in the phenotypes of living organisms (Ceci and Williams 2000).

In recent years, however, this static view has given way to a more dynamic model in which the environment itself determines whether and how specific genes are expressed (Ridley 2004), a phenomenon known as epigenetics (Allis et al. 2007). As a result, current scientific debates tend not to be over which is more importantgenes or the environmentbut about how genes and the environment interact to bring about the expression of certain inherited proclivities. The focus of current work in both the biological and behavioral sciences has thus shifted to gene-environment interactions (Rutter 2006). The environment not only shapes behavior through learning and physiological conditioning, but also by determining which certain genes get turned on or off, and hence, expressed or not (Costa and Eaton 2006). Scientists have now documented instances where the environment has changed an organism's genetic structure to create a new genotype that is passed on to progeny through a process known as methylation (Suzuki and Bird 2008; Champagne 2012).

Environmental circumstances are especially important in understanding outcomes among human beings, given the complexity of their genome and the importance of learning in shaping their behavior. Unlike most organisms, however, the critical environment for human beings is not physical, but social. Since the emergence of Homo sapiens around two hundred thousand years ago, human adaptation has primarily been through culture rather than through genetics (Massey 2005a). Prior to the advent of the genus Homo, our ancestors occupied a very restricted environment both geographically and climatically, one essentially confined to the savannahs of East Africa. With the arrival of Homo sapiens, however, culture became the primary mechanism of adaptation and human beings quickly came to occupy virtually every ecological niche in the globe (Cavalli-Sforza, Menozzi, and Piazza 1994).

Human beings do not interact directly with the physical environment, but through the intervening filters of culture and society; and since cultural practices and societal institutions are socially transmitted, the critical environments for understanding the expression of human traits and behaviors are thus social. It is within specific social contexts that learning occurs and human proclivities play out. In order to explain human outcomes, therefore, one must consider the social ecology of developmentthe series of social environments that people come to inhabit at different stages of the life cycle (Bronfenbrenner 1979).

Everyone is born into a kinship system, of course, and the family is thefirst social environment all human beings occupy. Newborn babies are helpless and would quickly perish without constant attention from family members, mostly the mother, but also the father, siblings, grandparents, and sometimes even more distant relatives. As children age and approach adulthood, they grow progressively less dependent on the family and more dependent on other social spheres such as neighborhoods, schools, and peers (Bronfenbrenner 1973). As adults, of course, humans face a social environment defined by a variety of macro social structuresgovernments, corporations, and other major social institutionsbut the capabilities that humans deploy in adapting to contingencies in the macro social environment are largely determined before adulthood through interactions that play out within micro social spheres.