The Cost of Honesty and the Fallacy of the Handicap Principle
Szabolcs Számadó
MTA-ELTE Research Group for Theoretical Biology and Evolutionary Ecology
Budapest, Hungary
[email protected]
ramet.elte.hu/~szamado
Plan

History

Theoretical background

Empirical evidence

Terminology
Prelude
Handicap Principle vs. Handicap signalling
The Handicap Principle is the set of claims made by Zahavi with regards of
biological signals.
Handicap signalling (costly signalling) is the idea published by Spence (1973) and
Zahavi (1975) that the honesty of signals can be maintained by signal cost.
The fisrt cannot hold without the second, but the second can hold without the first.
Extravagant signals in nature
Proposed solution
Handicap principle – Amotz Zahavi (1975) Mate selection: a selection for handicap
Singals have to be costly in order to be honest - Wasteful signalling
The handicap principle is a very simple idea: waste can make sense, because by wasting one
provides conclusively that one has enough assets to waste and more. The investment –the waste
itself- is just what makes the advertisement reliable.” - Zahavi & Zahavi, 1997, pp. 229.
What was the claim?
Handicap principle
1, It is the equilibrium cost payed by the honest signallers that creates
a high enough potential cost for cheaters.
„ The other kind of selection, by which signals evolve, results in costly features and traits that look like
‘waste’. It is precisely this costliness, the signaller’s investment in the signals, that makes signals reliable. ”
Zahavi & Zahavi, 1997, pp. 43
2, Some part of this equilibrium cost is wasteful.
„ waste can make sense, because by wasting one provides conclusively that one has enough assets to waste
and more” Zahavi & Zahavi, 1997, pp. 229.
3, This is the only mechanism that can create such cost.
„Signal selection differs from sexual selection that it involves all signals” Zahavi & Zahavi, 1997, pp. 43
“The handicap principle is an essential component in all signals” Zahavi, 2008; pp. 2
What gave legitimacy to these claims?
Alan Grafen (1990) Biological signals as handicaps
1, Explicit verbal support:
“Zahavi's major claims for the handicap principle are thus vindicated.” Grafen, 1990, abstract
2, The famous second condition of Grafen’s main handicap results:
a, signalling is honest,
b, signals are costly,
c, signals are costlier for worse signallers.
3, Note that despite verbal support Grafen (1990) made a more limited claim
(even though this never was recognized/accounted for):
Informative vs. persuasive signals (shared vs. conflict of interest)
Indices, „revealing handicaps” (he just did not called them signals!)
„all persuasive signals have to be handicaps”
What gave legitimacy to these claims?
Theoretical models show that Grafen’s main handicap results do not hold:
1) signalling need not be honest, not even on average (Számadó, 2000)
2) signals need not be costly, not even under conflict of interest (Hurd,
1995; Számadó, 1999; Lachmann et al., 2001)
3) signals need not be costlier for worse signallers (Getty 2006).
Current state of the the claims
Theoretical background
Handicap principle:
1, It is the equilibrium cost payed by the honest signallers that
creates a high enough potential cost for cheaters.
2, Some part of this equilibrium cost is wasteful.
Theoretical background
Action-response game (Maynard Smith, 1991; Hurd, 1995; Számadó, 1999)
give
give
not to give
signal
signal
low
high
start
not to signal
not to signal
give
not to give
Mother nature
signaller
receiver
not to give
give
not to give
Hurd, 1995; Számadó, 1999
Conditions specified by Grafen 1990
Theoretical background
Conditions of honesty:
Wl +r Vl<0
Wh+rVh>0
Vl+rWl<Cl
Vh+rWh>Ch
Vl+rWl>0
Vh+rWh>0
Equilibrium cost
Cl = Ch
Maynard Smith, 1991
This result holds for continuous models as well -Lachmann et al., 2001
Theoretical background
1. It is not the equilibrium cost of signals that maintains honesty.
2. The equilibrium cost of signals need not be wasteful not even under conflict of
interest.
Current state of the the claims
Theoretical background
Handicap principle:
3, This is the only mechanism that can create such cost.
Mechanisms that can maintain low equilibrium cost for honest signallers even
under conflict of interest (Számadó, 2011):
1. Indices
2. Performance displays
3. Pooling equilibria
4. Frequency dependent selection
5. Proximity risk
6. Punishment of cheaters
7. Inclusive fitness cost
8. Individual recognition
Empirical evidence
Empirical evidence
Efficacy cost
Maynard Smith and Harper, 1995
Strategic cost
Empirical evidence
Minimal cost
Cost-free
Handicap
cost:
Efficiacy
Strategic
cost-free
negligible
no
minimal cost
yes
no
handicap
yes
yes
Empirical evidence
There is no methodology to tell apart the efficacy and the strategic cost
of signals!
There is no solid empirical evidence in favour of handicap signalling.
Empirical evidence
Measuring equilibrium cost is not informative:
1, It is not the equilibrium cost payed by honest signallers that maintains
honesty.
2, It does not tells us what part of this equilibrium cost is the strategic cost,
if any.
If we measure positive equilibrium cost the signal need not be a
handicap.

If we measure zero equilibrium cost it still might be the case that it is the
signal cost that maintains honesty.

Empirical evidence
There is trade-off between immunological functions and signalling.
1, Trade-off need not implies cost.
Empirical evidence
There is trade-off between immunological functions and signalling.
1, Trade-off need not implies cost.
Empirical evidence
2, We do not what part of the cost is the strategic cost, if any.
=
?
=
Terminology
1. Handicap = cost (not useful)
2. Handicap = signal with strategic cost (not needed, cannot be measured)
3. Handicap = cost that maintains honesty (cannot be seen at the equilibrium)
4. Get rid off the term “handicap” (and efficacy and strategic cost)
5. Use game theory to define the term!
Hurd, 1995; Számadó, 1999
Conditions of honesty:
Wl +r Vl<0
Wh+rVh>0
Vl+rWl<Cl
Vh+rWh>Ch
Vl+rWl>0
Vh+rWh>0
Equilibrium cost
Cl = Ch
Maynard Smith, 1991
Handicap is the part of the equilibrium cost paid by honest signallers that results
from the constraint that links Cl to Ch.
Terminology
Theoretical necessity
Biological constraint
It fits the original idea:
1. Equilibrium cost
2. Equilibrium cost paid by honest signallers
3. It is a waste (it results from constraints).
Summary
1. It is not the equilibrium cost of signals that maintains honesty.
2. The equilibrium cost of signals need not be wasteful not even under conflict of
interest.
3. The are plenty of alternative mechanisms that can maintain the honesty of
communication even under conflict of interest.
4. Handicap/costly signals can be still plentyful in nature, however, there is no
empirical evidence that would strongly support this claim.
Thank you!