Transcript chapt01_evo_variation

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
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.
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
Primate Adaptations
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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
Walking Upright
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African forest became grassland 5 million years ago
Bipedalism (standing & walking on 2 legs) evolved
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Adaptations for bipedalism
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pelvis, femur, knee, great toe, arch, skull, vertebrae, etc.
Australopithecus (2.5mya) gave rise Homo habilis
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spot predators, carry food or infants
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
Primate Phylogeny
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
Perception; things aren’t always
what they seem
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)
The palmaris muscle
Dextrocardia
Human Function
• Characteristics of life
– organization
– cellular composition
– excretion
– metabolism
– responsiveness and movement
– homeostasis
– development (growth or differentiation)
– reproduction
– evolution
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
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
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
Negative Feedback Loops
• Mechanism to keep a variable close to its set
point
• Body senses a change & activates
mechanisms to reverse it
Negative Feedback, Set Point
• Room temperature does not stay at set point
of 68 degrees -- it only averages 68 degrees
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
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
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
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
You have the weapons of
knowledge go forth and conquer all