dissipating, the power of the family. Thus, the rules for royalty were to marry their relatives, namely, other royalty.
The practice of intra-marriage among royalty is taken as proof of the genetic basis for the incest taboo, because the Royal Family of England, and its relatives, experienced repeated occurrences of hemophilia in its lineage. However, if a family has no genes for hemophilia, incest will not produce it. The consequences of incest depend on the genes of the family. Positive results of incest are responsible for the development of crops and breeding of animals, like dogs and horses.
Incest is assumed to be genetically detrimental, because mating with close relatives causes more pairing of recessive alleles than would a random match from the general population. However, human mating is not random. We tend to pick mates who are like us and, therefore, are related or at least share many genetic characteristics. Each person has two parents, four grandparents, eight great grandparents, etc. The expansion of ancestors doubles for each past generation. However, in a few generations the number of possible ancestors (2n) exceeds the population of the Earth in the past. Thus, we all must share common ancestors and be related. Most importantly, the idea that pairing recessives is bad comes from the idea that recessive is evil and dominant is good. Dominant and recessive are merely terms expressing which gene will evidence in the phenotype, when they occur in combination. Dominant and recessive do not mean good and evil, because the mutations that produced the genes were random and without regard for the needs of the organism. Natural selection determines the adaptive value of the alleles, not human social values. Positive, negative, or neutral consequences from incest would depend on the genetic lineage of the mates. A genetic pairing with detrimental recessives would tend to evidence those characteristics in incest. But a positive lineage would evidence those positive characteristics. Thus, the incest taboo has no genetic basis, but was produced by the important social values of human mating.
Significance of Evolution for Behavior
Hardy-Weinberg also explained the normal distribution of structural characteristics, like height and weight, in terms of the possible gene combinations at mating. Thus, for one pair of genes, the binomial expansion, (A + a)2, gives the frequency of possibilities (A2 + 2Aa + a2). A and a are the probability of occurrence of each gene allele (A + a = 1). With increasing numbers (n) of gene alleles, and estimates of the numbers of gene alleles in a population can be large, the frequency of possibilities (A + a)n approaches the normal distribution. For an imaginary, because all organisms have thousands of genes, single-gene organism with one dominant (A) and one recessive (a) gene allele, the mating possibilities of the population can be seen in Table 1-3.
Table 1-3 Gene Frequencies for Aa Type Parents.
The tabulated totals for Table 1-3 are: 1AA + 2Aa + 1aa. Graphically represented, the tabulated totals would look like Figure 1-2.
Figure 1-2 Graph of the Tabulated Frequencies of 1AA + 2Aa + 1aa.
For another imaginary, again, because all organisms have thousands of genes, dual-gene organism with two dominant (A, B) and two recessive (a, b) gene alleles, the mating possibilities of the population can be seen in Table 1-4.
Table 1-4 Gene Frequencies for AaBb Type Parents.
The tabulated totals for Table 1-4 are
1AABB + 1AAbb + 2AABb + 2AaBB + 4AaBb + 2Aabb + 2aaBb + 1aaBB + 1aabb.
Graphically represented, the tabulated totals would look like Figure 1-3.
Figure 1-3 Graph of the Tabulated Frequencies of 1AABB + 1AAbb + 2AABb + 2AaBB + 4AaBb + 2Aabb + 2aaBb + 1aaBB + 1aabb.
With just the two genes graphed in Figure 1-3, the shape is beginning to arrange into the familiar “bell curve” of the normal distribution. Increasing the number of genes determining a characteristic to a great many, as is typical, produces a normal distribution. Modern knowledge of genes is that they also interact and turn on and off, resulting in complex function. Thus, gene content results in the normal distribution of characteristics.
Life sciences typically employ structure to document the evolution of species, because structure leaves bodily or fossil records. Genes determine structure, which, in turn, determines behavior. Human genes mean we have arms, not wings, and that determines our behavior. But what most people, even many life scientists, fail to realize is that behavior determines the genes of the next generation through reproduction. Natural selection is the environment, which has no way of interacting with genes or structure. What natural selection actually selects is neither the genes that determine structure nor the structure that determines behavior, but the behavior itself. The behavior of an organism is what interacts with the environment. The behavior of the organism interacting with the environment selects which organism reproduces and, thus, establishes the genes, subsequent structure, and consequent behavior for the next generation, as illustrated in Figure 1-4. The evolution of any species is, therefore, as much an evolution of behavior as of structure. Behavior is, actually, the central feature of evolution because it is the focus of selection.
Figure 1-4 The cycle of the behavior of the organism interacting with the environment, selecting which organism reproduces and, thus, establishing the genes, subsequent structure, and consequent behavior for the next generation.
Therefore, behavioral characteristics, like aptitudes, also display a normal distribution. Behavior, structure and genes are inseparable in evolution. The evolution of a species could be traced by its behavior as well as by its genes or its structure. But, following the evolution of an organism by its behavior, using the fossil record is exceedingly difficult, because the behavior died with the organism. However, some behavior can be inferred from structure, like large canine teeth indicate a predator and extensive molars mean a grazing animal.
Courtship pattern is an excellent example of the evolution of behavior. Successful courtship leading to reproduction is extremely adaptive and highly favored by natural selection, because that behavior produces the next generation. Unsuccessful courtship, like mating across species, is selected against because such behavior creates, at most, sterile hybrids and does not contribute to the next generation. Any structure or behavior that leads to sexual attraction and subsequent successful courtship is favored. Repeated favoring of such advantages has led to very elaborate mate-attracting structures and extremely complicated courtship rituals in many species. The intricate courting “dances” of many birds are a dramatic example of the evolution of behavior.
Darwin (1871) was puzzled by mate choice because he thought that such behavior provided a direction in evolution separate from natural selection. Modern theorists also give a separate role to sexual selection (Daly and Wilson, 1978). Trivers (1972) felt that parental investment in offspring would influence sexual selection, even in humans. Thus, males would tend to be more polygamous,
