CHAPTER What Are the Origins of Brain and Behavior? 1The BrainThe BrainGross anatomy of the nervous systemBehavior • Complexity of behavior varies considerably in different species Simple Nervous System Complex Nervous System Narrow Range of Behavior Wider Range of BehaviorBehaviorAristotle,*Descartes,*and*Darwin:**brain*and*behavior* r ela5onship • Ancient Greece: Aristotle – MentalismAristotle,*Descartes,*and*Darwin:**brain*and*behavior* r ela5onship* • Descartes • Dualism • Mind-Body ProblemAristotle,*Descartes,*and*Darwin:**brain*and*behavior* r ela5onship* • Darwin • Materialism • Natural SelectionAppearance of New Trait (e.g. via mutation) Adaptive Trait Increases Chances of Survival Trait Passed on to Offspring How are traits are selected naturally?Evolution of Brain and Behavior Origin of Brain Cells and Brains • Despite the age of the Earth (4.5 billion years), brain cells and brains are quite recent adaptations – First forms of life: 3.5 billion years ago – First brain cells: 700 million years ago – First brain: 250 million years ago – First human-like brain: 6 million years ago – Modern human brain: 200,000 years agoEvolution of Brain and Behavior Classification of Life • Taxonomy: branch of biology concerned with naming and classifying species Taxonomy of Modern humansEvolution of Brain and Behavior Evolution of Animals Having Nervous Systems Five different kingdomsEvolution of Brain and Behavior Evolution of Animals Having Nervous Systems • Nerve net: • Segmented nerve trunk: • Ganglia: • Chordates: – Notochord:Evolution of Brain and Behavior The Chordate Nervous System • Nervous systems vary widely among chordates, but all: – Bilaterally symmetrical and segmented – Brain and spinal cord encased in cartilage/bone – “Crossed” organization – Spinal cord lies behind the heart and gutEvolution of Brain and Behavior The Chordate Nervous System • Behavioral complexity among chordates is related to the evolution of cerebral hemispheres and cerebellum.Evolution of the Human Brain and Behavior Humans: Members of the Primate Order Features common to primates:Evolution of the Human Brain and Behavior Humans: Members of the Primate Order • Humans and chimpanzees share a common ancestor 5 – 10 million years agoEvolution of the Human Brain and Behavior The First HumansEvolution of the Human Brain and Behavior Relating Brain Size and Behavior Jerison (1973) • Principle of Proper Mass:Evolution of the Human Brain and Behavior Climate Change and the Enlarging Hominid Brain • Three-fold increase in brain size over last 5 million years appears to have taken place in steps.Modern Human Brain Size and Intelligence • Evolutionary Approach – Make brain-behavior comparisons between different species • CAUTION: – Difficult to make brain-behavior comparisons between members within the same species • Example: Brain size and intelligenceModern Human Brain Size and Intelligence Are people with larger brains more intelligent? Problems with answering this question: • How does one measure brain size?Studying Brain and Behavior in Modern Humans Fallacies of Human Brain-Size Comparisons • How does one measure intelligence? – People vary enormously in their individual abilities, depending on the task Person A • Excellent math abilities • Poor spatial abilities Person B • Poor math abilities • Excellent spatial abilities Which person is more intelligent?Studying Brain and Behavior in Modern Humans Fallacies of Human Brain-Size Comparisons • Brain size and intelligence do not seem to be particularly related – Research has shown that many smart people (e.g., Einstein) have average size brains – Women’s brains weigh about 10% less than men, but the two sexes do not differ in measures of average intelligence • Culture: – Learned behaviors that are passed on from one generation to the next through teaching and learning • The brain is highly flexible – We perform many tasks today that our brains were not originally selected for early during