Physiological vs Psychological Dichotomy

• The physiological vs psychological dichotomy rose to prominence in the Western world after the Medieval Ages
• Scientific knowledge accumulated during the Renaissance was at odds with Church dictates
• René Descartes argued that physical matter (the brain) could be observed scientifically
• Descartes believed that the mind (soul) has no physical substance and is thus under the scope of religion
• Cartesian dualism was sanctioned by the church and the idea that the human brain and the mind are separate entities became even more accepted

The Problem with Dichotomies

• Complex psychological changes can be produced by damage to, or stimulation of parts of the brain

The Case of the Man Who Fell Out of Bed

• A patient woke and felt a severed, hairy, warm human leg in his bed

• The patient thought a nurse put it there as a joke

• The patient threw the leg out of bed, but somehow ended up on the floor with it attached to him

• The patient became agitated, and Dr. Sacks tried to comfort him

• Dr. Sacks asked him where his left leg was, if the one attached to him wasn't it

• Looking pale, the patient replied that he had no idea where his own leg was it had disappeared

• Some nonhuman species, particularly primate species, possess abilities that were once assumed to be purely human, such as self-awareness

Inherited or Learned?

• For centuries, scholars have debated if behavioral capacities are inherited or acquired through learning: the nature-nurture issue
• Most early North American psychologists committed to the nurture side of the issue
• John B. Watson is the father of behaviorism
• European ethology focused on instinctive behaviors

The Problem with Dichotomies (Redefinition)

Behavior always develops under the combined control of both nature and nurture

Behavioral Development

• Ontogeny: Development of individuals over their life span
• Phylogeny: Evolutionary development of species through the age

Evolution

• Modern biology began in 1859 with the publication of Charles Darwin's On the Origin of Species

Three of Darwin's Supporting Evidence

• Darwin documented the evolution of fossil records through recent geological layers

• He described striking structural similarities among living species, which suggested that they had evolved from common ancestors

• He pointed to the major changes that had been brought about in domestic plants and animals by programs of selective breeding

• Evolution occurs through natural selection: Heritable traits associated with high rates of survival and reproduction are likely passed on

• Repeated cycles of this process lead to evolution of species better adapted to surviving and reproducing in their particular environmental niche

Mechanisms of Behavior

• Social Dominance: Males of a species often establish a hierarchy of social dominance, sometimes through combat
• The dominant male usually copulates more than lower-ranked males
• Courtship Display: The male usually signals to the female to elicit a response, though copulation may fail if one of the pair fails to react appropriately to the signal

Behavioral Development (Experiments)

• Robert Tryon theorized that behavioral traits can be selectively bred

Tryon's Rat Maze Experiment

• He experimented with rats by teaching them how to run a maze
• He mated the males and females that entered incorrect alleys least frequently (maze-bright) and those that entered incorrect alleys most frequently (maze-dull)
• By the 8th generation, the worst of the maze-bright strain made fewer errors than the best of the maze-dull

Genetics of Human Psychological Differences

• All human traits are highly heritable
• Similar family environments contributes little to the diversity of behavioral traits
• A Minnesota study of twins had results that showed that even if monozygotic twins were raised in different family environments, they were substantially more like one another than fraternal twins

Behavioral Development (Genetic Disorders)

• Phenylketonuria (PKU) is a neurological disorder from a genetic mutation, where low levels in the amino acid phenylalanine can lead to intellectual disability if untreated
• PKU Was discovered by the Norwegian dentist Ivar Asbjørn Følling when he noticed that the urine of his mentally retarded children had a peculiar odor because their urine showed high levels of phenylpyruvic acid

The separation of physiological and psychological aspects gained prominence after the Medieval Ages. Descartes proposed that while the brain is physical and observable, the mind is non-physical and under religious purview. Brain damage can cause complex psychological changes.