Biological Bases of Behavior

Psychology Overview

• Psychology: The science of behavior and mental processes.

  • Behavior: Any observable action an organism does.

  • Mental Processes: Internal, subjective experiences (sensations, perceptions, dreams, thoughts, beliefs, feelings) that cannot be observed.

• Central Principle: Everything psychological is also biological. Every thought, mood, action, and urge is due to an internal biological event.

The Nature-Nurture Issue

• The most persistent debate in psychology, focusing on the relative contributions of genes (nature) and experience (nurture) to psychological traits and behaviors.

  • Modern View: Traits and behaviors are seen as an interaction between nature and nurture.

Natural Selection

• Definition: Inherited traits that enhance survival and reproduction in a specific environment are more likely to be passed on to future generations.

  • Proposed by: Charles Darwin in The Origin of Species (1859).

  • In the 20th century, this theory was misused to justify discriminatory ideas, such as eugenics (selective breeding to promote specific traits).

Branches of Psychology

1. Evolutionary Psychology

   • Studies the evolution of behavior and the mind using natural selection principles.

   • Focuses on how humans are alike.

2. Behavior Genetics

   • Studies the influence of genetics and environment on behavior.

   • Focuses on how humans differ.

   • Concept: "Nurture works on what nature provides" — biology sets the framework, and the environment shapes it.

     • Example: A person may be biologically predisposed to depression (nature) and grow up in poverty (nurture), increasing the likelihood of developing depression.

Evolutionary Psychology: Understanding Human Nature

• Goal: To explain behavior tendencies using natural selection.

  • Organisms' varied offspring compete for survival.

  • Certain traits increase reproductive and survival chances.

  • Survivors pass their genes to the next generation, leading to changes in population characteristics over time.

Natural Selection & Adaptation Example

• Dmitry Belyaev's Experiment:

  • Mated 100 female foxes and 30 male foxes, selecting and mating the tamest 20% of offspring.

  • Over 40 years, this selective breeding led to a new, tamer breed of foxes.

Mutation and Genetic Adaptation

• Mutation: A random error in gene replication that causes a change.

  • If a mutation has a positive effect, it increases the likelihood that the mutated gene will be passed on.

• Genes provide the capacity to adapt to new environments; when combined with experiences, they enhance fitness (ability to survive and reproduce).

Evolutionary Success and Human Similarities

• Only 5% of genetic differences among humans come from population differences; 95% of genetic variation exists within populations.

• Differences between two individuals from the same population (e.g., two South Africans) are often greater than the average difference between individuals from different populations (e.g., a South African and a Singaporean).

Behavior Genetics: Predicting Individual Differences

• Behavior Geneticists: Study the genetic and environmental origins of human differences.

  • Focus on the interaction between:

    • Environment: All non-genetic influences, from prenatal nutrition to experiences with people and surroundings.

    • Heredity: The genetic transfer of traits from parents to offspring.

      • Genes: Biochemical units of heredity.

      • Genome: Complete set of genetic instructions for making an organism.

• Common sequences in human DNA are what make us human, but we share 96% of our DNA with chimpanzees.

• Key Point: Many genes of small effect influence our differing traits.

Twin and Adoption Studies

• Used to understand the impact of nature (genetics) and nurture (environment).

  • Identical (Monozygotic) Twins: Develop from a single fertilized egg that splits, creating genetically identical individuals.

    • While they have the same genes, they may not have the same number of gene copies.

    • About one-third of identical twins have different placentas, affecting their prenatal environment.

  • Fraternal (Dizygotic) Twins: Develop from separate eggs and are genetically no closer than regular siblings, but share a prenatal environment.

• Behaviorally and physically, identical twins are more similar than fraternal twins.

  • Studies use identical twins separated at birth to measure environmental impact.

• Key Point: Shared family environments have little effect on personality, but parenting does influence other factors.

Gene-Environment Interaction

• Interaction: The interplay between heredity and environment, where the effect of one factor depends on the presence of another.

• Epigenetics: The study of how environmental factors (e.g., diet, drugs, stress) can influence gene expression without changing the DNA sequence.

  • These changes can be passed down through generations (e.g., stress effects on Holocaust survivors).

Parts of the Brain

• Frontal Lobe

  • Movement of the body

  • Personality

  • Concentration, planning, problem solving

  • Meaning of words

  • Emotional reactions

  • Speech

  • Smell

• Parietal Lobe

  • Touch and pressure

  • Taste

  • Body awareness

• Occipital Lobe

  • Sight

• Cerebellum

  • Fine motor (muscle) control

  • Balance and coordination

• Temporal Lobe

  • Receive & processes sound

  • Recognizing faces

  • Emotion

  • Long term memory

• Limbic Lobe

  • Located inside the brain

  • Controls emotions like happiness, love, and sadness

• Corpus Callosum

  • Connects the two hemispheres

• Hypothalamus

  • Master part of the brain

• Pituitary Gland

  • Gland “Master Gland” - controls growth

• Pons

  • sleep, coordination & facial expressions

• Medulla

  • life functions

• “RAS” - Reticular Activating System

  • regulates arousal

• Thalamus

  • routes all incoming senses except smell

• Hippocampus

  • process explicit memories (facts & events)

• Amygdala

  • Linked to fear, anger & aggression

• Wernicke’s Area

  • Comprehension of language & speech

• Broca’s Area

  • controls productions of speech

Neurons Role & Function

Parts of A Neuron

• Dendrites - branch-like structures that receive signals from the neurons

• Soma - also known as the cell body, is the main part of a neuron were info is processed

• Axon - A long, thin fiber that carries electrical impulses away from the cell body to other neurons

• Myelin Sheath - A fatter layer that insulates the axon, speeding up the transmission of signals.

• Terminal Buttons The end of axon where neurotransmitters are released into the synapse

• Synapse - also known as cleft or gap, the crucial gap between neurons where communication occurs.

• Neurotransmitters - Chemical messengers released by the terminal buttons that cross the synapse to transmit signal to the receiving neuron.

• Synaptic Vesicles - Found within the axon terminal of presynaptic neuron. Stores and releases neurotransmitters when stimulated by an action potential.

Important Neurotransmitters

Excitatory Neurotransmitter - chemical secreted at terminal button that causes the neuron on the other side of the synapse to generate an action potential (to fire).

Inhibitory Neurotransmitter - chemical secreted at terminal button that reduces or prevents neural impulses in the postsynaptic neuron