Homeostasis

• Walter Cannon 1932 “The Wisdom of the Body”

• Jame Lovelock ~1969 Gaia hypothesis (Lovelock, J.E.; Margulis, L. (1974). "Atmospheric homeostasis by and for the biosphere- The

Gaia hypothesis". Tellus 26 (1): 2–10.

• Draw a causal lop diagram describing a self regulating component of the human body.

Example

• Draw a causal loop diagram to describe the following:

• The sun becomes brighter causing Earth to warm to a new equilibrium temperature.

sunlightEarth’s mean Temperature

Emitted infrared energy+

-

-+

Coffee System

Tc

TR

The hotter the coffee isThe faster it cools

Tc-TRCooling Rate

The higher the cooling rateThe colder the coffee

Cooling Rate Tc-TR

+

-

Coffee System

Tc

TR

The hotter the coffee isThe faster it cools

Tc-TRCooling Rate

The higher the cooling rateThe colder the coffee

-

+ - = -

Negative connection

The higher the cooling rateThe colder the coffee

Cooling Rate Tc-TR

-Tc

TR

Positive connection

The hotter the coffee isThe faster it cools

Tc-TRCooling Rate+

Tc

TR

Negative feedback loop

Tc

TR

The hotter the coffee isThe faster it cools

Tc-TRCooling Rate

The higher the cooling rateThe colder the coffee

-

+ - = -

Cools with a characteristic time constant, minutes

Homeostasis is internal balance

Equilibrium

Stable equilibrium (negative feedback)

Unstable equilibrium (positive feedback)

• ,

PerturbationsSmall changes that disturb a system from its equilibrium state.

Hot Plate Hot Plate

A simple Earth

Heating rate

TE

A simple Earth

Heating rate

TE

Albedo

Absorbed solar

Complete the system diagram

• Daisy World simulation

Daisy World

Ave

rage

sur

face

Tem

p

Daisy coverage

TsDaisies

TsDaisies Albedo

Daisy World

Average surface Temp

Ts Daisies

Dai

sy c

over

age Ts Daisies

Daisy World

Average surface Temp

Ts DaisiesD

aisy

cov

erag

e Ts Daisies

albedo

P1

P1

Ts Daisies

albedoP2

P2

Daisy World Model