The Handy Psychology Answer Book. Lisa J. Cohen

In large monkey troops, for example, high-status females and their offspring have many advantages over lower-status females.

      The presence of monogamy can also affect female-to-female competition. Monogamy is more common when a prolonged or intensified period of dependence in the young favors paternal investment in child rearing. When males are monogamous, they are likely to be more selective in their choice of a mate as they invest more in each partner. Hence females may need to compete for males. In these cases, females who show signs of greater reproductive fitness are often more successful in attracting males. We can certainly consider how this might apply to human females, who characteristically spend considerable energy and time maintaining and enhancing their physical attractiveness to males. Across human cultures, the standards for female beauty almost universally relate to youth and physical health, which corresponds to a long period of fertility.

      If we consider the size of the beauty industry, which produces women’s makeup, jewelry, clothing, skin creams, hair products, and many other forms of female adornment, we can see how evolutionary pressures may be at play within our own culture.

      How do scientists test the evolutionary significance of behavior?

      In the absence of rigorous scientific research, sociobiologists can potentially fall back upon speculation, which can easily be biased by prevailing prejudices. In this way a scientist could assume that women are supposed to be subordinate to males; males are supposed to be aggressive. Therefore it is critical that rigorous scientific research support any claims as to the evolutionary significance of human behavior.

      Sociobiology relies on careful animal studies in which the frequency of any given social behavior can be correlated with some marker of evolutionary significance. For example, the frequency of altruistic behavior in baboons can be correlated with the degree of biological relatedness between animals, which will then translate into the proportion of shared genes (50 percent for parents and children, 50 percent for full siblings, 25 percent for half siblings, and 12.5 percent for cousins).

      In humans, twin studies have been used to differentiate the effects of genetics from the effects of environment. Additionally, anthropological studies that compare social behavior across different cultures are also used in an attempt to separate the effects of genetics and environment. If the same behavior is found across very different cultural contexts, it is likely that these behaviors have a genetic basis. These studies become harder to do with time, however, as globalization leaves fewer cultures truly independent of each other.

      How do twin studies help illuminate the role of genetics?

      Twin studies are one common method used to tease apart the contributions of genetics vs. environment in human traits. Many twin studies have focused on IQ tests, comparing monozygotic (identical) and dizygotic (fraternal) twins. Monozygotic twins grew from the same fertilized egg and share 100 percent of their genes. Dizygotic twins grew from two separate eggs and therefore share only 50 percent of their genes. Twins reared together and twins reared apart have also been compared. These studies show that intelligence does have a significant genetic component, as monozygotic twins score much more similarly on IQ tests than do other types of siblings. However, these studies have been criticized because while the percentage of genes that differ from one subject to another has been carefully measured, the degree that environments differ between subjects is not clear at all. Moreover, there is considerable evidence showing that many environmental factors, such as socio-economic status, years of education, and mother’s level of education also have very strong influences on IQ.

      Studies comparing identical twins, fraternal twins, and non-twin siblings have been used in an attempt to tease apart the role of genes and environment in various psychological traits.

      NEUROBIOLOGICAL THEORIES

      What are neurobiological theories of psychology?

      Neurobiological theories of psychology investigate the links between the brain and the mind. The assumption is that all psychological processes can be linked to specific patterns of brain activity and that understanding the neurobiological substrates of behavior can only enhance our understanding of human psychology. With the remarkable technological advances of recent years, our ability to study the workings of the brain and its relationship to psychological processes has grown at an extremely rapid pace.

      What is neuropsychology?

      Neuropsychology involves the study of specific psychological functions that can be directly linked to brain processes. Alexander Luria (1902–1977), one of the fathers of neuropsychology, studied brain-injured soldiers in World War II to determine how different kinds of brain damage impacted intellectual functioning. Modern neuropsychological research helps identify the specific psychological functions that are associated with specific patterns of brain activity. For example, the encoding of information into long-term memory is mediated by a brain area called the hippocampus.

      How do neurobiological theories of psychology dovetail with evolutionary psychology?

      Animal models are a critical aspect of neurobiological research because scientists can perform much more invasive procedures on animal brains than on human brains. However, the ethics of animal research is a controversial and difficult area. Studies of animal brains shed important light on the workings of the human brain but they also highlight the ways that brains differ across species. When the brains of various animal species are compared, we can generate hypotheses about how our own brains developed across evolution. For example, the frontal lobe, which is associated with planning and other complex cognitive functions, is proportionately larger and more convoluted (providing more surface area) in animals with higher intelligence. This suggests that the frontal lobe grew in size across human evolution as intelligence became an increasingly important evolutionary strategy.

      How do advances in brain imaging technology affect neurobiological theories of psychology?

      Only a few decades ago, it was not possible to observe the human brain in action. Autopsies after death and neuropsychological studies of brain-injured patients were the main methods of neurobiological research. With the advent of brain imaging technology, however, it became possible to obtain snapshots of the living human brain. Computerized tomography (CT scans) and magnetic resonance imagery (MRI) allowed pictures of brain anatomy. Positron emission tomography (PET) and single photon emission computed tomography (SPECT) scans allowed investigation of the actual workings of the brain via recorded patterns of glucose uptake or blood flow.

      More recently, functional MRI (fMRI) allows rapidly repeated images of brain activity, permitting study of brain activity over time. In effect, brain imaging technology has moved from still photos to moving pictures. Moreover, subjects can be scanned while performing various actions, opening up an enormous array of research possibilities that will take many years to fully explore.

      How does a PET scan work?

      PET scan was one of the earlier brain scanning technologies and now has largely been eclipsed by fMRI technology. PET scans work by measuring the decay of a radioactive tracer that has been injected into the blood stream prior to the scan. This allows scientists to map the brain areas with the greatest amount of blood flow. It is assumed that high rates of blood flow in a particular area indicate increased brain activity at that location. PET scans are used to compare blood flow patterns across groups (e.g., in patients with schizophrenia vs. healthy controls) or across activities (e.g., viewing images of drug paraphernalia vs. a nature scene). These days fMRI methodology is used far more frequently than PET because it is less expensive, does not involve radioactive tracers, and has better resolution both across time and across space. In other words, fMRI provides more precise visual information and can take more scans in the same amount of time. But PET still has some important advantages over fMRI. This