Behavioral Genetics: Chapters
Preface and Introduction
This book is an introduction for non-scientists to the science of behavioral genetics and its broader ethical and social implications. Among the topics covered are how scientists explore the influence of genes and environment on behavior and how such research may challenge our understanding of human nature, personal responsibility, and equality. It is a product of a project on behavioral genetics conducted by the American Association for the Advancement of Science (AAAS) and The Hastings Center. The introduction covers how genes and environments interact through development to shape differences in mood, personality, and intelligence
Chapter 1: What Is Behavioral Genetics?
Seers, prophets, and astrologers of ancient times have tried to predict behavior. Writers such as Shakespeare and Jane Austen have tried to describe it. Freud, Jung, and other psychiatrists have sought to explain it. Today’s advice columnists assume they understand it, ministers sermonize about it, and some daytime TV talk show hosts provoke their guests into the worst of it. Yet much of behavior remains a mystery. It’s the unusual person (the differently behaving person) who has not tried to understand his or her own behavior or the behavior of others. Therefore, it should come as no surprise that many scientists choose to study behavior.
Chapter 2: The Human Genome
The complete set of genetic material for any organism is called its genome. In recent decades, information about the genomes of several organisms has been pouring out of a massive international effort called the Human Genome Project. This “sea of data,” as it has been called, confirms the view that genes operate within really big and complex systems.The human genome is organized into two sets of twenty-three chromosomes, forty-six in all. These chromosomes are made of a chemical substance called DNA (deoxyribonucleic acid), and this DNA, in turn, is made of smaller units: nirogen containing molecules called nucleotides or bases. There are four different bases, called adenine (A), cytosine (C), thymine (T), and guanine (G). The bases are paired and linked together to form a double-stranded helix. The order of bases strung along chromosomal DNA is critical, as we will explain in a moment.
Chapter 3: Environment Illustrated
Three examples will illustrate how environments impinge upon genes. They concern a plant, a human disease, and a human behavior. In a classic experiment, seven genetically distinct yarrow plants were collected and three cuttings taken from each plant. One cutting of each genotype was planted at low, medium, and high elevations, respectively. When the plants matured, no one genotype grew best at all altitudes, and at each altitude the seven genotypes fared differently. For example, one genotype grew the tallest at the medium elevation but attained only middling height at the other two elevations. The best growers at low and high elevation grew poorly at medium elevation. The medium altitude produced the worst overall results, but still yielded one tall and two medium-tall samples. Altitude had an effect on each genotype, but not to the same degree nor in the same way.
Chapter 4: Animal Studies
The “teacher’s pet” of behavioral genetic research is the common fruit fly, Drosophila melanogaster, and some 2,000 related species. The fruit fly is a favorite of researchers for simple reasons. Fruit flies are easy to collect and keep: just bait a jar with overripe fruit and trap them. They reproduce rapidly and copiously; the time span from egg to adult is less than two weeks and one female produces hundreds of offspring. Fruit flies willingly cooperate in researchers’ efforts to selectively breed them and to run them through all sorts of experiments. What’s more, fruit flies do not bite and do not transmit disease to humans, and researchers do not need to obtain government approval to ensure that the research protects the flies’ rights and privacy.
Chapter 5: Genotype/phenotype Complexity
Many genes interact with many physical and social environments to shape normal traits, but one gene misfiring is sometimes sufficient to produce disorder. This is the case with Alzheimer’s disease – which we will get back to in a moment — but also with other medical conditions. An example is the rare dementing illness called Huntington’s disease, which destroys the fatty lining of nerve cells leading to loss of coordinated movement, emotional instability, psychosis, and mental decline. Huntington’s is a dominant disorder, meaning that only one disease-related allele at a single locus need be present for the disease to manifest itself. A gene on Chromosome 4 is implicated in Huntington’s. (The chromosomes are numbered in order of their relative length; 4 is a relatively big chromosome.) However, this disease does not result from a single mutation to this gene. Rather, many different alleles for the gene lead to the same problematic result. These alleles differ from each other in one important way: they have a different number of tandem repeats — multiple copies of the same base sequence (sometimes called “stutters”).
Chapter 6: Impulsive Behavior and ADHD
There is a saying that a weed is merely a plant out of place. The same could be said of many character traits. The boisterous person might be out of place in a monastery dedicated to silence but not in the stands at a basketball game. Boisterousness, its counterpoint meekness, and many other aspects of personality are undesirable traits only when they create problems for the person displaying them or for others who interact with that person.
Chapter 7: Defining Intelligence
Smart. Quick-witted. Sharp. Clever. Astute. The English language has many words that describe intelligence, which briefly defined is the ability to absorb, process, recollect, and apply information. Cognition is the word used by scientists to specifically refer to the process of thinking.