Evolution and Human Survival Lecture 4 PSY391S John Yeomans Diversity of Life Forms • Categorization by phenotypes. • Linneaus: Species, genus, family, order class, phylum, kingdom. • Which features are most important in making groups? • Can the same principles be used to make other groups? • How were these groups formed? Diversity of Ancient Life • Geology: Older fossil forms in deeper sediments. • Changes in size, structure and design imply family histories. Evolution. • Variety of habitats and fossils. Beagle. • How did species evolve over millions of years? • Darwin: “Survival of Fittest” Evidence for Theory • Historical Record: Wars, famines, diseases, habitat lossselection. • Movement of species to new habitats new structures, e.g. lungs, legs, hair. • How did this happen in prehistory? • Selective breeding of domestic animals-- pigeons, cows, dogs. Speciation • Finches in Galapagos--Darwin and Grants. • When do phenotype differences become species differences? • How did humans diverge from primates? • Why did Neanderthals or other primates die? How to Survive? • “We are the accumulation of mechanisms that allowed our ancestors to survive and to reproduce their genes” (Sagan) • “Accumulation” includes functional and vestigial systems. DNA also an accumulation. • Who were our ancestors who managed to survive and reproduce? • The Selfish Gene: All our systems and strategies are shells for helping our genes survive. • Biological Purpose of Life? Human Strategies • Survival: Kill others genes and save your own? Humans survive by social cooperation rather than “dog eat dog”. • Reproduction: Have the most offspring possible? Humans have the fewest--single births, long immature period--but highest survival rate. • Learning and specialization--Civilization. • Aggression? Yes, but not to disrupt social organization. Classification and Gene Lineages Lecture 5 PSY391S John Yeomans Classification by Phenotype • Which features are most important? Little agreement. • Principles of comparing different groups? • Where is change from species to genus to family etc, if evolution is continuous? • Genes are more fundamental, in theory, than any surface features. • Quantitative rather than qualitative. Classification by Genes • Hybridization of DNA samples (Wilson). • Complete sequences, genomes. • Similarities in genes from flies to humans imply common lineages. • Reconstruction of family trees: Are all bases equally important? • Is DNA mutation rate constant? • Genetic Clock~ 1%/5 million years. Human Family History • Females: Mitochondrial DNA is preserved from mother to daughter. 16,569 bases. • Trace human origins to Eve? Neanderthals? • Males: Y chromosome is preserved from father to son. Trace family lineage. • Trace DNA in all humans to extract lineages around the globe. Human Genes • Which DNA makes us different from primates? E.g. prodynorphin. • Are some genes more important? • Which genes affect hands, brain, speech? • Could a few genes lead to larger brains? CNS Evolution--Invertebrates • Nerve nets: Action potentials, reflexes. • Ganglia chains: Molluscs, worms, arthropods. • Giant neurons and axons--no myelin. • Head ganglia are fused. Lecture 6: Evolution of Brain • Mammalian brain properties • Brain size vs. body weight • Ancient brains--when did they get bigger? • Human brains--when did they get bigger? Vertebrate CNS • Protected brain and spinal cord. • Myelinated axons saves space for more neurons. • Shift from midbrain, cerebellum and olfaction to limbic system then cerebral cortex. Brain Size and Body Weight Equation • Log Brain Weight=0.7(log Body Weight)+b • Or: Brain Weight = K(Body Wt)0.7 • Power function linear on log-log plot. • Some mammals have extra brain size (Humans and dolphins 8X extra) • K = encephalization factor. All Vertebrates Ancient Vertebrates • Brain weight from endocranial space. • Body weight from leg bone diameter. • Ancient reptiles same as modern reptiles, except for Archeopteryx (bird-like predator). • Modern birds and mammals increased brain capacity by 4X over ancient birds and mammals (still 4X reptiles). • Warm blood favors brain evolution? Encephalization Evolution of Human Brain • Increased by 3X about 1-2 million years ago. • Most of change in frontal cortex. • Neoteny: Do we sustain embryonic brain growth for longer by keeping neonate features?