Human Origins and Adaptations

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Human Origins and Adaptations

• Charles Darwins 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

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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

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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

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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

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Primate Phylogeny
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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

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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)

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The palmaris muscle
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Dextrocardia
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Human Function

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

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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

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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

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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

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Negative Feedback Loops

• Mechanism to keep a variable close to its set
  point
• Body senses a change activates mechanisms to
  reverse it

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Negative Feedback, Set Point

• Room temperature does not stay at set point of 68
  degrees -- it only averages 68 degrees

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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

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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

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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

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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