Download Human Adaptation and Variation The logic of selection

Adaptation by natural selection: the only source
of design in nature.
HB2215/2282
Biological Anthropology:
Human Adaptation and Variation
The logic of selection:
Generate-test-replicate
Design? Really?
Design: “to formulate a plan for; to create or
contrive for a particular purpose or effect; to
have a goal or purpose”
Adaptation: aptus = “suited” or “fit” ad = “to”
…suited to environment for what?
Does natural selection plan or design?
Does it have a goal?
Does a thermostat have a goal?
Algorithm:
• a step-by-step problem-solving procedure; a precise
rule or set of rules specifying how to solve some
problem; a detailed sequence of actions to perform
to accomplish some task
• a certain sort of formal process that can be counted
on - logically - to yield a certain sort of outcome
whenever it is 'run' or 'instantiated‘ (Dennett 1995 Darwin’s
Dangerous Idea)
Control system:
A mechanical, optical, or electronic (logical) system
that is used to maintain a desired output
Room
too hot
Room
too cold
Bi-metallic
strip
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Thermostat as algorithm or
control system:
1 Assess room temperature
(via bimetallic strip)
2 Compare room
temperature (where it is)
with set-goal (where it
should be)
3 Use comparison as
output to approach setgoal (< = furnace on; > =
furnace off)
Thermostat
Set-goal = 20°
A thermostat is control system designed to
accomplish the task of maintaining temperature.
A thermostat is a control system that is used to
maintain a desired heat output.
Control systems in human biology:
• maintain body temperature at 37°
• maintain blood sugar at 90mg of glucose/
100ml of blood
• maintain blood pressure at around
120/70mmHg
Thermostat “intends”
temperature to be 20 °
Process of adaptation by natural selection is
a non-designed designer.
Process of adaptation by natural selection is an
algorithm or control system that maintains life.
Adaptation by natural selection “intends” organisms
to be suited to their environments so that they
can reproduce (ie, life continues).
What designed the control systems that control
body temperature, blood sugar and blood
pressure?
1
Good match
with environment
Rear
Pro
Adaptation by natural
selection as algorithm or
control system:
1 Assess environment (via
its effects on organism)
S
2 Compare effects of
environment on organism
Rear
(where it is) with set-goal
(where it should be)
Pro
3 Use comparison as
G&D output to approach setgoal (< = no S, G&D, Pro
S
or rear; > = continue with
life cycle → reproduce)
G&D
Phenotype;
Poor match
organism
with environment
Adaptation by natural selection
Set-goal = reproduction, fitness
3 Use comparison as output to approach set-goal:
• are all relevant molecular, biochemical, metabolic,
etc. control systems working properly?
• is organism surviving?
• if so, are all relevant physiological and endocrine
control systems working properly?
• is organism growing and developing?
• if so, are all relevant psychoneuroendocrine
control systems working properly?
• is organism producing and rearing offspring?
• if so, whole process continues and selection
retrospectively endorses DNA at apex of parents’
life cycle
Selection “intends”
organisms to reproduce
Mother nature (natural selection) can be viewed
as having intentions, in the limited sense of having
retrospectively endorsed features for one reason
or another.
Dennett 1995. Darwin’s Dangerous Idea (p. 462)
“Retrospective endorsement” = reproduction
• copying genes into next generation
• copying genes includes possibility of
mutation and recombination = introduces
variability
The logic of selection – adaptation by natural selection
as a control system: match between phenotype and
set goal → output copy of DNA
The process of adaptation: the “GTR heuristic”
G = generate variability
T = test, select variants
R = replicate, copy variants that
have passed test, been selected
Heuristic = “serving to find out”
The GTR heuristic is a mechanism for representing
information (“knowledge”) about the environment
in the phenotype.
Information about
the environment
(laws of aerodynamics)…
…represented in the
phenotype of birds…
Information about
the environment
(laws of optics)…
…represented in eyes
…and airplanes
…and telescopes
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Q: But how does information get into the phenotype?
A: Development = gene x environment interaction
over time.
Genes = nature
Environment = nurture
A devil, a born devil, on whose nature
Nurture can never stick… (Shakespeare)
The logic of selection
• GTR heuristic: r =
a. genetics
b. epigenetics (gene expression)
c. individual experience, reasoning
d. culture (shared meaning)
• embodied information about environment
• environment of evolutionary adaptedness (EEA)
• adaptationist/mechanist
• adaptationist: how selection works
• mechanist: how organisms work
Prospero, describing Caliban
The Tempest, Act IV, Scene I.
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