1. The indirect nature of genetic influences on behavior Genes are simply DNA molecules that provide the code for building the body’s proteins. Variation in genes across species provides the basis for species-typical behaviors, and variation in genes among members of a species is one source of individual differences in behavior within a species. But genes never produce behaviors directly. Genes always work in conjunction with the environment, and so their effects depend on environmental conditions. Neither genes nor environment “determines” our behavior. Our behavior results from an interplay between the environment in which we live and our bodies’ biological mechanisms, which themselves were built through an interplay between genes and environment.
2. The unconscious nature of distal functions Sigmund Freud (discussed in Chapters 15 and 17) is famous for his claim that we are often unconscious of the real reasons for our actions. On that point, at least, modern evolutionary psychologists and Freud agree. Our species-typical drives and behavioral tendencies evolved to promote functions related to survival and reproduction, but we rarely think of those functions, and we are often completely ignorant of them.
Toddlers toddle and play with words because it is “fun” to do so, without any thought about the value of such play in learning to walk and talk. We all smile, automatically or because it seems like the right thing to do, when we are happy or when we meet someone, without thinking about the functions that smiling might serve. When we fall in love, we are far more likely to attribute that feeling to the sweet, charming, and irresistible nature of the beloved person than to anything having to do with the value of bonding for producing and raising children. When we feel jealous because of attention another is paying to our beloved, we think angry thoughts about betrayal and unfaithfulness, not about the role of jealousy in preserving monogamy. When we help a person in need, we do it out of felt sympathy and compassion; we do not coldly, consciously calculate the costs and long-term benefits to ourselves.
The reasons we give ourselves for what we do are an aspect of the proximate causation of our behavior. We are often no more aware of the distal functions of our actions than the cabbage butterfly is of why it is irresistibly drawn to plants of the cabbage family as the only proper place to lay its eggs.
3. Evolution as an integrative theme in psychology The evolutionary perspective provides the broadest view that we can take in psychology. It is concerned with the origins and distal functions of all aspects of human nature (and the nature of other animals). It is a perspective that can be applied to the whole vast range of topics with which psychology is concerned. All of the complex biological mechanisms that underlie our psychological nature came about because they helped our ancestors to survive and reproduce. We can expect, therefore, that all of our basic motivational and emotional mechanisms are biased toward generating behaviors that promote survival and reproduction; and we can expect that our sensory, perceptual, memory, and reasoning mechanisms are biased toward picking up and using information essential to those purposes. We are not general learning or thinking machines that indiscriminately analyze all information available; we are biological survival machines designed to use information selectively to achieve our ends. As you go through the rest of this book, crossing the whole range of psychology, you will see this idea applied in every chapter.