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Evolution of the Brain and Behavior. 6 Evolution of the Brain and Behavior. Why Should We Study Other Species? How Closely Related Are Two Species? Comparative Methods Help Us Study the Biological Mechanisms of Behavior. 6 Evolution of the Brain and Behavior.
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6 Evolution of the Brain and Behavior • Why Should We Study Other Species? • How Closely Related Are Two Species? • Comparative Methods Help Us Study the Biological Mechanisms of Behavior
6 Evolution of the Brain and Behavior • Nervous Systems Differ Widely in Structure • The Evolution of Vertebrate Brains Can Be Related to Changes in Behavior • Evolution Continues Today
6 Why Should We Study Other Species? A phylogenyis the evolutionary history of a particular group of organisms and may be represented as a family tree. Different species show different solutions to environmental changes. Living animals, along with fossils, allow study of the body and brain.
6 How Closely Related Are Two Species? In Linnaeus’s system of classification, each species has two names: • Genus – a group of species that resemble each other • Species Linnaeus classified animals according to anatomical features, not ancestry.
6 How Closely Related Are Two Species? Naturalists, students of animal life and structure, began to doubt that species were created separately. Fossils of extinct species provided evidence for evolution – the gradual change of a species.
Figure 6.2 Linnaean Classification of the Domestic Dog (Part 1)
Figure 6.2 Linnaean Classification of the Domestic Dog (Part 2)
Figure 6.2 Linnaean Classification of the Domestic Dog (Part 3)
6 How Closely Related Are Two Species? A mechanism for evolution was missing: • Lamarck proposed theinheritance of acquired characteristics – experience caused changes in offspring, later proven false • Darwin and Wallace proposed evolution by natural selection– a theory that says evolution proceeds by differential success in reproduction
6 How Closely Related Are Two Species? Darwin’s hypothesis: • Reproduction will increase a population rapidly unless factors limit it. • Individuals of a species are not identical. • Some variation is inherited. • Not all offspring survive to reproduce.
6 How Closely Related Are Two Species? Darwin also inferred that variations among individuals affect the probability that they will survive and reproduce – evolution through natural selection. Sexual selection – each sex has anatomical and behavioral features that favor reproductive success.
6 How Closely Related Are Two Species? Mutations are spontaneous changes in genes, a rapid form of evolution. Genetics – the study of the mechanisms of inheritance – began with Mendel and DeVries. Drosophila reproduce rapidly and allowed the study of chromosomes – assemblies of DNA.
6 How Closely Related Are Two Species? Through the discovery of the structure of DNA by Franklin, Watson, and Crick, scientists realized that DNA is the means of inheritance. Both gradual changes within a species and the formation of new ones can be explained through natural selection and genetics.
6 How Closely Related Are Two Species? Taxonomy – the classification of organisms A fossil record can help date an organism. DNA analysis can quantify the differences between species, and also estimate their divergence from a common ancestor, through the rate of DNA decay.
6 How Closely Related Are Two Species? Convergent evolution shows similarities in behavior or structure among unrelated animals due to adaptations to similar environments. Homoplasy is the resemblance between features such as body shape due to convergent evolution.
6 How Closely Related Are Two Species? Homology is a similarity based on common ancestry, as are forelimbs. Analogy refers to similar function – a human hand and an elephant’s trunk are analogous – even though they look different.
6 Comparative Methods Help Us Study the Biological Mechanisms of Behavior BMW&Benz : Brain & Behavior Differences in brain size and structure can be due to behavioral adaptations. Novel or strategic food-seeking behavior is correlated with larger brain size. Animals who depend on hearing, vision, or memory for their food develop larger related brain structures.
Figure 6.5 Food Storing in Birds as Related to Hippocampal Size
6 Comparative Methods Help Us Study the Biological Mechanisms of Behavior Mammals’ lifestyles are related to cortical organization: Behavioral function brain () rat’s whiskers platypus bill
Box 6.1 (A) To Each Its Own Sensory World • Nocturnal rats that use whiskers have a large part of their cortex devoted to their whiskers, but only a little to vision.
Box 6.1 (B) To Each Its Own Sensory World • The platypus uses its bill to detect mechanical and electrical stimuli – most of its somatosensory cortex is devoted to the bill.
6 Nervous Systems Differ Widely in Structure Nervous systems vary widely in structure and complexity. Structures include nerve nets, simple ganglia, optic lobes and the cerebral cortex.
6 Nervous Systems Differ Widely in Structure Mammals share main brain structures. Differences between human and rat brains are in actual and relative size of regions, such as cerebral cortex and olfactory bulbs. Human neurons are larger.
6 Nervous Systems Differ Widely in Structure Vertebrate nervous systems share features: • Developed from a dorsal neural tube • Bilateral symmetry • Segmentation • Hierarchical control • Separate peripheral and central systems • Localization of function
6 Nervous Systems Differ Widely in Structure Reasons to study certain species: • Outstanding features, like sensory skill • Convenience • Comparison • Preservation • Economic importance • Treatment of disease
6 Nervous Systems Differ Widely in Structure Insect nervous systems are similar: • A brain with three compartments – two protocerebrum lobes and an optic lobe • Ganglia in each body segment • Giant axons that conduct action potentials quickly
Figure 6.9 The Nervous System of a Typical Insect, Drosophila melanogaster
6 Nervous Systems Differ Widely in Structure Features of vertebrates and invertebrates: • Basic plan – both have central and peripheral nervous systems • Both have a brain • Number of neurons – vertebrates have more neurons devoted to information processing, while invertebrates have fewer, but larger neurons
6 Nervous Systems Differ Widely in Structure • Ganglion structure – vertebrate ganglia have cell bodies inside and processes out – invertebrate ganglia have cell bodies outside and a neuropil, or network, within • Axons and neural conduction – invertebrates do not have myelinated axons
6 Nervous Systems Differ Widely in Structure • Structural changes – changes in invertebrates during metamorphosis are more dramatic than changes during vertebrate development • Location in the body – the CNS in vertebrates is in the skull and spinal column – in invertebrates it is built around the digestive tract
6 The Evolution of Vertebrate Brains Can Be Related to Changes in Behavior Two methods are used to study evolution of the brain: • Endocast – uses a fossil skull to make a cast of the brain • Living animals – allows for the study of the internal structure of the brain: the nuclei, fiber tracts, and circuitry
6 The Evolution of Vertebrate Brains Can Be Related to Changes in Behavior In vertebrates, brain differences exist in size and elaboration of common structures: • Cerebellar hemispheres are smaller in reptiles (體大腦小) than in birds (體小腦大) • Reptiles are the 1st species to have cerebral cortex. • Vision in animals may rely on the midbrain, the optic tectum, or on the telencephalon • All animals have a six-layered isocortex
6 The Evolution of Vertebrate Brains Can Be Related to Changes in Behavior The encephalization factor is a measure of brain size relative to body size. The relationship between brain weight and body weight is similar for all classes of vertebrates. Brain weight relative to body size does vary between and within classes.
Figure 6.11 The Relationship between Brain Weight and Body Weight (Part 1)
Figure 6.11 The Relationship between Brain Weight and Body Weight (Part 2)
6 The Evolution of Vertebrate Brains Can Be Related to Changes in Behavior Brain evolution shows size changes both in specific regions and overall. The size of each brain structure is highly correlated with the total brain size. However, the rate of increase in some brain areas can differ between small and large brains.
Figure 6.14 Changes in the Apportionment of Brain Regions among Primates
6 The Evolution of Vertebrate Brains Can Be Related to Changes in Behavior Australopithecines were hominids that made and used tools. The ability to use tools reduced the necessity for large jaws and teeth, and those became steadily smaller.
6 The Evolution of Vertebrate Brains Can Be Related to Changes in Behavior As Homo erectus evolved, brains became larger and faces got smaller. Homo erectus made elaborate tools, used fire, and hunted. They also expanded their area over three continents (long-distance moving). With Homo sapiens, brain volume had reached modern levels.
