o the “nature versus nurture” concept describes the contrast between heredity and environment.
• Ex. your genotype might include a gene for blonde hair and another for brown (genotype is the two alleles), but your phenotypical, or observable trait of hair color is light brown hair.
o each cell contains the instructions for an entire human organism, but only a subset of instructions is expressed at any given time and location.
o Many alleles can occur for a given gene, but a single individual receives only two, one from each parent.
• However, in many cases, one allele does not entirely dominate another. (ex – getting light brown hair instead of dark brown or blonde)
o 22 of the 23 pairs of human chromosomes from each parent are perfectly matched (each gene has a corresponding gene on its partner). The remaining pair, the X and Y sex chromosomes, does not carry the same genes.
o Most of the genes located on the Y chromosome are involved with male fertility.
o The X chromosome contains genes not duplicated on the Y chromosome that influence a wide variety of characteristics.
o Generally, if a female receives a healthy gene on the X chromosome from one parent and a defective gene on the X chromosome from her other parent, she will be a carrier of the condition, but will not experience it herself. (the healthy X chromosome will offset the other unhealthy X chromosome)
o In contrast, a male receiving a defective gene on the X chromosome from his mother will have the condition. Because there is no equivalent gene on the Y chromosome to offset the defective recessive gene, it will be expressed.
• as a result, conditions such as hemophilia and red-green colorblindness are much more frequent among males and referred to as sex-linked characteristics.
o When factors other than the genotype itself produce changes in a phenotype, we say that an epigenetic change has occurred.
o Epigenetic change often works by influencing gene expression, the process by which the DNA forms proteins that contribute to features of living cells. The environment can determine if and when a particular gene is activated.
o Epigenetic change provides a clear example of how the human mind responds to the interplay between nature and nurture.
• These links can help explain individual differences between human beings as well as the differences we see between our species and others.
o Heritability is usually presented as a ratio of the amount of variation observed in a population due to genetics relative to the total amount of variation due to both genetic and environmental influences.
2) Heritability cannot be assessed without taking the environment into account. If the environment is held constant (everybody is treated exactly the same way), the heritability of a trait will appear to be high – because the heritability will be exaggerated. In variable environments, heritability will be lower.
3) Another common misunderstanding of behavioral genetics is the belief that we can identify a “gene for” a particular behavior (ex. the “gene for” alcoholism).
• The human genome is the product of millions of years of evolution.
o Darwin found this because he was well aware of the procedures used by farmers to develop animals and plants with desirable traits by mating particular individuals to each other.
• Darwin suggested that the pressures of survival and reproduction in the wild would make the choice determining which traits are passed along to the next generation, a process he named natural selection.
• Organisms that survive long enough to reproduce would pass their traits along to the next generation. Organisms that did not reproduce would not have the opportunity to pass their traits along to future generations.
* Natural selection favors the organism with the highest degree of fitness.
o Mutant alleles that provide some advantage often spread through the population, but most mutant alleles that result in a disadvantage disappear from future generations.
o The average human baby is born with 130 new mutations, but the vast majority have no effect.
o phenotypical traits that are advantageous in one environment might be less so in another
o This concept of fitness includes survival to adulthood, ability to find a mate, and reproduction.
o Fitness describes the interaction between characteristics and the environment in which they exist. – we need to consider nature within the context of nurture.
o Fitness varies across environments – characteristics such as long ears and long legs work in hot, desert climates, but short ears and legs conserve heat in colder climates.
o Adaptations can take many forms: they can be behaviors (such as jumping higher to avoid a predator) or anatomical features (such as eyes that can see color).
o Any adaptations that are “good enough” to contribute to the fitness of an organism will carry forward into future generations.
o A classic example of very rapid adaptation is the case of the English peppered moth
• This rapid brain evolution suggests that improved intelligence was quickly translated into substantial advantages in survival.
• The major factor distinguishing human intelligence from the intelligence of other species is the richness and complexity of the social behavior supported by the human brain.
• The challenges that humans face and our social behavior required the evolution of a special brain.
However, the brain has not changed much over the past centuries. Although it continues to evolve, it is not really growing.
• It is likely that environmental factors, including nutrition and education, might account for the improvement of our brains.
• The evolutionary psychology approach is a direct descendant of the functionalism supported by William James.
o Functionalism implies that behavior is seen as promoting survival, as opposed to being random and pointless.
• The goal of evolutionary psychology is to explain how the patterns of behavior we share with other human beings have been shaped by evolution.
• One of the outstanding features of human beings is our rich and essential social nature.
• To understand the evolution of social behavior, we need to explore its advantages for survival and reproduction.
Selfishness (one wins through cheating, the other loses)
Altruism (one chooses to lose for the benefit of the other)
Spite (both lose)
o altruism is widespread in the animal kingdom.
o Darwin stated, “A tribe including many members who, from possessing a high degree the spirit of patriotism, fidelity, obedience, courage, and sympathy, were always ready to aid one another, and to sacrifice themselves for the common good would be victorious over most other tribes; and this would be natural selection.”
o In cases of reciprocal altruism, it is customary to help another individual when you can reasonable expect the other individual to return the favor at some future date.
• Sexual selection is influenced by the different investments in parenting made by males and females.
• The mother can maximize her children’s chance of survival by choosing a father who will not only pass along healthy genes but will participate in the raising of children.
o Women have the ability to make very accurate predications of a man’s interest in children, simply by looking at a photograph of his face. Men with facial features correlated with high testosterone are viewed as less likely to participate in childrearing than are men with facial features correlated with lower testosterone.
• ex. male deer engage in fights that determine which males are able to mate and which are not
• ex. the coloration on peacocks.
• Human cultures arise from knowledge that is transmitted socially – through social interactions.
• Experiences shaped by culture, like other types of experiences, interact with survival and reproductive pressures.
• The evolutionary approach, however, suggests that another type of compatibility is important for romantic relationships – a compatibility of genes that contribute to the immune system.
o Looking at a cluster of genes known as the major histocompatibility complex (MHC), shows our tendency toward sexual selection. This type of sexual selection operates on traits in one sex that influences the choices by others.
o Different configurations of the MHC genes produce distinctive body odors that are easily detected and distinguished from one another. Men and women prefer smells associated with MHC genotypes that were different than their own.