Human Origins and Adaptations

1. Human Origins and Adaptations • Charles Darwin’s theory of natural selection explains how species originate and change through time • On the Origin of Species by Means of Natural Selection (1859) • The Descent of Man (1871) discussed human evolution & our relationships to other animals • Changed our view of our origin, our nature & our place in the universe

2. Evolution, Selection, and Adaptation • Evolution is change in genetic composition of a population of organisms • development of bacterial resistance to antibiotics, new strains of AIDS virus and emergence of new species • Theory of natural selection • some individuals have hereditary advantages (adaptations) enabling them to produce more offspring • if they pass these characteristics on it brings about a genetic change in the population (evolution) • forces that favor some individuals over others are called selection pressures -- climate, disease, etc.

3. Adaptations • Adaptations are useful features that evolved in response to selection pressures • DNA hybridization suggests a difference of only 1.6% in DNA structure between humans & chimpanzees • Evolutionary developments help explain some aspects of our anatomy (vestigial organs) • piloerector muscle in the skin have no use • auricularis muscles do not move in most people • help us chose animals for biomedical research

4. Primate Adaptations • Some human features can be traced to the earliest primates • Squirrel-sized, insect-eating mammals became arboreal probably due to safety, food supply & lack of competition • shoulder became more mobile (reach any direction) • thumbs became opposable to encircle branches with thumb & fingers (prehensile) • forward-facing eyes provide depth perception • judge distances accurately for leaping & catching prey • color vision to distinguish ripe fruit • larger brains & good memory to remember food sources

5. Walking Upright • African forest became grassland 5 million years ago • Bipedalism (standing & walking on 2 legs) evolved • spot predators, carry food or infants • Adaptations for bipedalism • pelvis, femur, knee, great toe, arch, skull, vertebrae, etc. • Australopithecus (2.5mya) gave rise Homo habilis • taller, larger brain volume, speech, tool-making • Homo erectus (1.1mya) and Homo sapiens (.3mya) • Homo sapiens include Neanderthal & Cro-Magnon • Evolutionary medicine traces our diseases to evolutionary past

6. Primate Phylogeny

7. Human Structure • Hierarchy of complexity • organism is composed of organ systems • organ systems composed of organs • organs composed of tissues • tissues composed of cells • organelles composed of molecules • molecules composed of atoms • Atoms compose molecules • Reductionism versus holism

8. Perception; things aren’t always what they seem

9. Anatomical Variation • No 2 humans are exactly alike • Missing organs • palmaris longus or plantaris muscles • More or less organs than normal • 2 spleens, single kidney, 6 or 4 lumbar vertebrae • Variation in organ locations (situs inversus, dextrocardia, situs perversus)

10. The palmaris muscle

11. Dextrocardia

12. Human Function • Characteristics of life • organization • cellular composition • excretion • metabolism • responsiveness and movement • homeostasis • development (growth or differentiation) • reproduction • evolution

13. How do you define Death? • When the heart stops? What about CPR? • Brain activity? What about Persistent Vegetative States (PVS) when people are awake, but unaware? Is there a particular part of the brain? • Organs can survive after the Organism Dies • Cell Lines like those from Henrietta Lacks are effectively immortal if cared for. • What evolutionary cause could there be? • Longest human life: 122 yrs • Clinical Death = no brain waves for 24 hours

14. Physiological Variation • Differs with sex, age, diet, weight, degree of physical activity • Typical human values • reference man • 22 years old, 154 lbs, light physical activity • 2800 kcal/day • reference woman • same as man except 128 lbs and 2000 kcal/day

15. Homeostasis • Hippocrates noted that body normally returns to a state of equilibrium by itself • needs to detect the change & oppose it • Walter Cannon (1871-1945) coined the term homeostasis indicating stable internal environment • Internal environment described as dynamic equilibrium • fluctuates within a range around a certain set point • Loss of homeostatic control causes illness or death

16. Negative Feedback Loops • Mechanism to keep a variable close to its set point • Body senses a change & activates mechanisms to reverse it

17. Negative Feedback, Set Point • Room temperature does not stay at set point of 68 degrees -- it only averages 68 degrees

18. Human Thermoregulation • Blood temperature sensing nerve cells in base of brain control shivering, sweating & vasomotor activity • vasodilation with heat & vasoconstriction with cold • Evaporation of water & heat radiation occur

19. Control of Blood Pressure • Rise in blood pressure detected • stretch receptors in wall of heart and major arteries • Nerve signals travel to cardiac center in brainstem • Nerve signals slow heart and lower blood pressure

20. Structures Needed for Feedback Loop • Receptor = structure that senses change • stretch receptors in heart & large blood vessels send information of an elevated BP to integrator • Integrator = control center • cardiac center in brainstem that signals heart to slow • Effector = structures that carry out commands of the control center • heart slows and BP decreases • sweating begins and evaporation cools the body

21. Positive Feedback Loops • Physiological change that leads to an even greater change in the same direction (self-amplifying) • Normal way of producing rapid changes • birth, blood clotting, protein digestion, generation of nerve signals

22. You have the weapons of knowledge go forth and conquer all