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Western Governors University
C180 Introduction to Psychology
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By the conclusion of this chapter, readers will be able to:
Understand the evolutionary basis of motivated behavior.
Explore how biological processes influence eating patterns.
Comprehend the biological mechanisms behind threat responses and aggression.
Analyze evolutionary explanations for mating behaviors.
Charles Darwin revolutionized scientific understanding with his theory of natural selection, detailed in On the Origin of Species (1859). His theory explains that species evolve across generations by favoring individuals better adapted to their environment. This theory remains essential in both biology and psychology for explaining human behavior.
What are the main components of Darwin’s theory?
| Key Points of Darwin’s Theory | Explanation |
|---|---|
| Overproduction | More organisms are born than can survive to reproduce. |
| Variation | There are individual differences within a species. |
| Adaptation | Some variations increase chances of survival and reproduction. |
| Inheritance | Beneficial traits are passed to offspring. |
| Limited Resources | Resources in the environment are finite. |
| Competition | Organisms compete for survival and reproductive opportunities. |
| Survival and Reproduction | Those with advantageous traits tend to survive and reproduce. |
| Speciation | Over time, accumulated changes can create new species. |
This framework illustrates how evolutionary pressures shape traits that enhance survival and reproduction, forming a biological basis for many behaviors.
The biological perspective in psychology explains behavior through the study of genetics, the brain, and evolution. It addresses key questions:
What behaviors are shared between humans and other species?
Behaviors like curiosity, cooperation, and play are common across many species, indicating evolutionary roots.
What behaviors are unique to humans?
Humans display complex language, abstract reasoning, and moral decision-making—traits linked to social and cultural evolution.
By understanding these shared and unique behaviors, psychologists trace how evolution shapes motivation, emotion, and cognition.
Human behavior results from a mix of biological inheritance and environmental influences. Studies on identical twins raised apart show remarkable similarities in temperament and intelligence, supporting the role of genetics.
This method compares human behaviors with those of animals to infer evolutionary origins. For example, aggression and social hierarchies in primates resemble those in humans, indicating these behaviors are partly genetic and adaptive rather than purely cultural.
The autonomic nervous system controls involuntary functions such as heart rate and digestion, linking biology to behavior.
| System | Function |
|---|---|
| Central Nervous System (CNS) | Coordinates mental and physical activity via brain and spinal cord. |
| Peripheral Nervous System (PNS) | Regulates involuntary functions through nerve networks beyond CNS. |
| Branches of ANS | Includes sympathetic and parasympathetic nervous systems. |
How do the sympathetic and parasympathetic systems differ?
| Sympathetic Nervous System | Parasympathetic Nervous System |
|---|---|
| Activated during stress (“fight or flight”) | Activated during rest (“rest and digest”) |
| Increases heart rate and energy mobilization | Slows heart rate and supports digestion |
| Causes vasoconstriction to conserve heat | Promotes vasodilation for cooling and nutrient absorption |
| Prepares body for emergency response | Restores balance and conserves energy |
These systems work together to maintain homeostasis by balancing responses to internal and external changes.
What biological responses occur during threat?
The sympathetic nervous system triggers the “fight-or-flight” response, including adrenaline release, faster heart rate, and heightened attention to prepare for danger.
Are there gender differences in aggression?
Males generally show more physical aggression influenced by testosterone, while females often display social or relational aggression, such as exclusion. Territoriality varies culturally, shaped by both biology and social norms.
Can aggression be learned?
Yes, aggression is not solely innate. Exposure to violent behavior through media or social settings can increase aggressive tendencies, indicating a mix of biology and environment.
What limits aggressive behavior?
| Mechanism | Description |
|---|---|
| Relative Strength | Weaker individuals avoid conflict with stronger opponents. |
| Dominance Hierarchies | Clear social ranks reduce conflict within groups. |
The debate centers on whether genetics (nature) or environment (nurture) primarily shapes behavior. Current research shows behaviors emerge from an interplay of both. For example, temperament may have genetic roots but is shaped by environmental feedback.
What role does physical appearance play in mate selection?
Physical attractiveness signals health and fertility. Across cultures, features such as clear skin, symmetry, and bright eyes are preferred, suggesting innate preferences even in infants as young as three months.
| Preference in Women | Significance |
|---|---|
| Waist-to-Hip Ratio | Indicates fertility and reproductive health |
| Pelvic Maturity and Fat Distribution | Reflects readiness for childbirth and overall health |
What is the matching hypothesis?
People tend to choose partners similar to themselves in attractiveness, personality, education, religion, and social status, fostering compatibility and reducing rejection.
How do mate preferences differ by gender?
| Men Seek | Women Seek |
|---|---|
| Physical attractiveness (fertility indicator) | Financial and social stability |
| Youth and health | Emotional commitment and kindness |
| Intelligence and humor | Intelligence and dependability |
| Less emphasis on commitment | Greater emphasis on long-term partnership |
| More jealousy over sexual infidelity | More jealousy over emotional infidelity |
These differences reflect evolutionary pressures and socialization patterns related to reproductive roles.
While evolutionary psychology provides valuable insights, it faces challenges. Many hypotheses are difficult to empirically test because psychological processes from ancestors leave limited evidence. Fossils reveal physical traits but not behaviors or mental states. Nevertheless, evolutionary theory encourages research that enriches understanding of human motivation and adaptation.
The biological perspective offers a crucial framework for understanding the physiological and evolutionary bases of behavior. It explains how genetics, brain structures, and hormones influence fundamental behaviors such as eating, aggression, and mating. However, integrating this with cognitive, social, and environmental perspectives is essential to fully comprehend human behavior.
| Contribution of the Biological Perspective | Description |
|---|---|
| Scientific basis for behavior | Explains biological systems underlying thought and emotion |
| Highlights evolutionary influences | Shows how survival and reproduction shape behavior |
| Encourages interdisciplinary integration | Recognizes the roles of environment, learning, and culture |
For example, obesity results from genetic predispositions combined with lifestyle, culture, and food availability—demonstrating gene-environment interaction.
Darwin, C. (1859). On the origin of species by means of natural selection. London: John Murray.
Stanford University Psychology Lectures. (n.d.). Psychology 1 Lecture 3: Biological Foundations of Behavior. Retrieved from http://www-psych.stanford.edu/~ashas/Psych1Lecture3.pdf
W. W. Norton & Company. (n.d.). Evolutionary psychology and biological foundations of behavior. Retrieved from www.wwnorton.com
