Biological Basis of Behavior

1. A Biological Basis of Behavior

2. • The Biological Approach to
Behavior
• Biological explanations of behavior raise the
issue of the relationship between mental activity
and the brain also know as the “mind-body” or
“mind-brain problem”
• The “mind-brain problem” has a variety of
explanations

3. • The Biological Approach to
Behavior
• Biological psychology: the study of the
physiological, evolutionary and developmental
mechanisms of behavior and experience
• A strong emphasis is placed upon brain
functioning

4. • The Biological Approach to
Behavior (cont’d.)
• Brain functioning can be explained at a more
microscopic level in terms of neuron and glia
activity
• Neurons and glia somehow produce an
enormous
wealth of behavior and experience

5. • Biological Explanations of
Behavior
• Biological explanations of behavior fall into four
categories:
– Physiological: relates a behavior to the
activity of the brain and other organs
– Ontogenetic: describes the development of
a structure or behavior
– Evolutionary: reconstructs evolutionary
history of a behavior or structure
– Functional: describes why a structure or
behavior evolved as it did

6. • Genetics and Behavior
• Both genes and environment interact to shape
human behavior
• The fundamental issue is how much a role each
factor plays in shaping human behaviors
– Examples: psychological disorders,
weight gain, personality, sexual
orientation

7. • Mendelian Genetics
• 19th century monk Gregor Mendel
demonstrated
that inheritance occurs through genes
• Genes are aligned along chromosomes (strands
of genes) and come in pairs
• A gene is a portion of a chromosome and is
composed of deoxyribonucleic acid (DNA)
• DNA serves as a model for the synthesis of
ribonucleic acid (RNA)

8. • Mendelian Genetics
(cont’d.)
• RNA is a single strand chemical that can serve as a
template/ model for the synthesis of proteins
• Proteins determine the development of the body
by:
• Forming part of the structure of the
body
• Serving as enzymes, biological
catalysts that regulate chemical
reactions in the body

10. • Mendelian Genetics
(cont’d.)
• Homozygous, for, a gene means that a person
has an identical pair of genes on the two
chromosomes
• Heterozygous, for a gene, means that a person
has an unmatched pair of genes on the two
chromosomes

11. • Mendelian Genetics
(cont’d.)
• Genes are either dominant, recessive, or
intermediate
– Examples: eye color, ability to taste
PTC
• A dominant gene shows a strong effect in
either
the homozygous or heterozygous condition
• A recessive gene shows its effect only in the
homozygous condition

13. • Mendelian Genetics
(cont’d.)
• Examples such as PTC and hair color can be
misleading
– Implies that a single gene
combination completely controls a
characteristic, but this is not true
• Some genes are only expressed partly: in some
cells and not others or only under certain
circumstances

14. • Types of genes include:
– Autosomal genes: all other genes
except for sex- linked genes
– Sex-linked genes: genes located on
the sex chromosomes
• In mammals, the sex chromosomes are
designated X & Y
– Females have two X chromosomes
(XX)
– Males have an X and a Y
chromosome (XY)

15. • During reproduction:
– Females contribute an X chromosome
– Males contribute either an X or a Y
chromosome that determines the sex of
the child
• If an X chromosome is contributed by the male,
the
offspring is female
• If a Y chromosome is contributed by the male,
the
offspring will be male

16. XY XX
X Y
X
XX XY

17. • Mendelian Genetics
(cont’d.)
• The human Y chromosome has genes for 27 proteins
• The human X chromosome has genes for
approximately 1500 proteins
• Thus, sex-linked genes usually refer to X-linked
genes: e.g., red-green color deficiency)
• Sex-limited genes are genes that are present in both
sexes but mainly have an effect on one sex (chest
hair, breast size, etc.)

18. • Genes change in several ways:
– Mutation: a heritable change in a DNA
molecule
– Microduplication/microdeletion: part of a
chromosome that might appear once
might appear twice or not at all
– Example: some researchers believe
schizophrenia might be a result of
microduplications and microdeletions of
brain-relevant genes

19. • Mendelian Genetics
(cont’d.)
• Epigenetics: a field that is concerned with changes
in gene expression without the modification of the
DNA sequence
• Some genes are active only at a certain point in
one’s life, a certain time of day, etc.
• Changes in gene expression are central to learning
and memory
• Epigenetic differences are a likely explanation for
differences between monozygotic “identical” twins

21. • Mendelian Genetics
(cont’d.)
• What you do at any moment not only affects
you now,
but produces epigenetic effects that alter gene
expressions for a longer period of time
• Experiences alter the activity of genes –
• *foods that we eat
• *stress

22. • Heredity and Environment
• Almost all behaviors have both a genetic
component and an environmental component
• Researchers study monozygotic (“from one
egg”) and fraternal (“from two eggs”) twins to
infer contributions of heredity and environment
• Researchers also study adopted children and
their resemblance to their biological parents to
infer hereditary influences

23. • Heredity and Environment
(cont’d.)
• Heritability refers to how much characteristics
depend on genetic differences
• Researchers have found evidence for heritability
in almost every behavior they have tested
• Heritability of a certain trait is specific to a given
population
• Strong environmental influences may cause
genetic influences to have less of an effect

24. • Heredity and Environment
(cont’d.)
• Traits with a strong hereditary influence can
by
modified by environmental intervention
– e.g., PKU: a genetic inability to metabolize
the amino acid phenylketonuria
– Environmental interventions can modify
PKU

25. • Heredity and Environment
(cont’d.)
• Genes do not directly produce behaviors
• Genes produce proteins that increase
the
probability that a behavior will develop
under
certain circumstances
• Genes can also have an indirect affect
– Genes can alter your environment by
producing behaviors or traits that alter
how people in your environment react
to you

26. • The Evolution of Behavior
• Evolution refers to a change in the frequency
of various genes in a population over
generations
• Regardless if helpful or harmful to the
species
• Evolution attempts to answer two questions:
– How did some species evolve?
– How do species evolve?

27. The Evolution of Behavior
(cont’d.)
• How species did evolve involves the tentative
construction of “evolutionary trees”
• How species do evolve rests upon some
assumptions:
– Offspring generally resemble their parents
for genetic reasons
– Mutations, recombination, and
microduplications of genes introduce new
heritable variations
– Certain individuals successfully reproduce
more than others do

28. • Artificial selection refers to choosing individuals
with desired traits and making them parents of
the next generation
• According to Darwin, nature also selects, and
successful individuals’ genes will be prevalent in
later generations

29. • Evolutionary psychology focuses upon
functional
and evolutionary explanations of how
behaviors
evolved
– Assumes that behaviors characteristic
of a species have arisen through
natural selection and provide a survival
advantage
• Examples: differences in peripheral/color
vision,
sleep mechanisms in the brain, eating habits,
temperature regulation

30. • Some behaviors are more debatable
regarding the
influence of natural selection
• Examples include:
– Life span length
– Gender differences in sexual
promiscuity
– Altruistic behavior: a behavior that
benefits
someone other than the actor
• Altruism is hard to find outside of
humans

31. Nature vs Nurture
Are you the way you are because you’re born
that way? Or is it because of the environment
you’re raised
Biology (genes) vs. Experience

32. • http://www.youtube.com/watch?v=W4N-
7AlzK7s
• http://www.youtube.com/watch?v=vHrmiy4
W9C0

33. • A gene only spreads if individuals with it
reproduce more than individuals without it
• A gene that benefits the species but not the
individual dies out with that individual
• Group selection is a controversial hypothesis
that states that altruistic groups survive better
than less cooperative ones
• Kin selection is the favored explanation:
selection for a gene that benefit’s the individual’s
relatives

34. • Reciprocal altruism is the idea that individuals
help those that will return the favor
• Building a reputation for helpfulness only
works
if others are willing to cooperate with you

35. • Animal research is an important source of
information for biological psychology but
remains
a highly controversial topic
• Animal research varies on the amount of
stress
and/ or pain that is caused to the animal itself

36. • Reasons for studying animals include:
– The underlying mechanisms of behavior are
similar across species and often easier to
study in nonhuman species
– We are interested in animals for their own
sake
– What we learn about animals sheds light on
human evolution
– Some experiments cannot use humans
because of legal or ethical reasons

38. • Opposition to animal research varies:
– “Minimalists” favor firm regulation on
research and place consideration upon the
type of animal used and the amount of
stress induced
– “Abolitionists” maintain that all animals have
the same rights as humans and any use of
animals is unethical

39. • Justification for research considers the amount of
benefit gained compared to the amount of
distress
caused to the animal
– No clear dividing line exists
• Colleges and research institutions in the United
States are required to have an Institutional
Animal
Care and Use Committee
– Oversees and determine acceptable
procedures