Contents - Konrad Lorenz Institute

An Evolutionary Model of the Effects of Human Paternal Resemblance on Paternal Investment
tion should be overwhelmingly negative. When the
two differ in relative proportions, an additive model
would predict negation, which might result in indifference
toward a child. Four different, discrete conditions
could arise and were tested in a follow-up study:
(1) a child shares no resemblance with dad and people
do not ascribe resemblance of the child to dad, (2)
a child shares no resemblance with dad, but people
ascribe resemblance of the child to dad, (3) a child
shares resemblance with dad, but people do not ascribe
resemblance of the child to dad, and (4) a child
shares resemblance with dad and people also ascribe
resemblance of the child to dad. When predicting the
behaviors towards the child and the viability of the
child in terms of paternal investment, the last option
would be the optimal condition and the first would
be the worst condition if the assumption of additivity
were adopted (see Figure 1 for a graphical depiction
of the predictions). PLATEK (2002) tested an interaction
between social mirror-mediated
information and actual shared resemblance and
found that males and females are affected similarly
by social mirror information, but only males appear
to be impacted by shared resemblance.
An exponent term, 1/i, could be added to the
equation to represent the number of offspring an
individual has. As can be seen, increases in the
number of offspring is predicted to yield decreases
in the amount of investment, or increases in abuse
by the male, because the probability that he has
been cuckolded has increased, because each additional
child that the mother bears represents an incidence
in which an EPC could have resulted in EPP
(BAKER/ BELLIS 1995; SCHACT/GERSHOWITZ 1963).
With one child the probability of cuckoldry modeled
here is GC k . With each additional child the
male faces the possibility that he was cuckolded
again; this would account for increases in the
amount of abuse seen with each subsequent child
in the birth order theorized here to be the result of
increased psychological strain on mechanisms designed
to assess resemblance and predict probability
of cuckoldry. Abuse related to birth order effects
has been demonstrated in humans (BURCH/GALLUP
unpublished data; DALY/WILSON 1982; REGALSKI/
GAULIN 1993). Further, additional children increase
the strain on that male’s resources. Additional children
represent increased costs; i.e., if he is now expected
to invest more (e.g., time, resources, etc.) in
offspring, this might occur at the cost of lost additional
mating opportunities.
PatI = P 1/i /C (4)
An Alternative Model: Deception
Detection and the Social Mirror
The paternal resemblance component in the above
equation assumes additive effects of actual and social
mirror resemblance; i.e., the above model assumes
that social mirror-mediated and actual paternal
resemblance sum to produce an effect that is the
probability of paternal investment. However, this
may not be the case. Females may try to manipulate
social mirror information to deceive males in to believing
that an offspring shares genes in common
with him and thus invest in offspring fathered by
another male (DALY/WILSON 1982; GAULIN, personal
communication; REGALSKI/GAULIN 1993). It would
have behooved females to assert paternal resemblance
if perceptions of resemblance translated to
increased investment on the part of the male and
that investment resulted in greater offspring survival.
However, a male who blindly trusted a female’s
assertions may have been at risk to invest in
offspring to whom he was genetically unrelated. As
a consequence of social mirror-mediated resemblance,
perhaps being an instance of deception on
the part of the female, it would have been in males’
best interests to evolve a deception detecting mechanism;
i.e., to question paternity when females enthusiastically
assert paternity. This counter model
can be modeled by subtly altering the original equation:
thus,
PatI = [(P rt )(IP rs Log 10 I) 1/i /C] = P' (5)
PatI = P'/C (6)
By representing social mirror-mediated resemblance
as the absolute value of the base 10 log of the
observed P rs , the return decreases the weight of the
paternal resemblance term of the equation, thus
lessening a male’s investment. When social mirrormediated
assertions of resemblance ensue this effect
is likely impacted by who is providing the information.
For example, it might be the case that, when
social mirror assertions are provided by the maternal
relatives, males might place lesser weight on
that information, and may even weight that information
negatively. However, when social affirmations
of resemblance are provided by the male’s kin,
positive weights might be applied and the social
mirror effect might have a greater impact on paternal
investment (see below).
Evolution and Cognition ❘ 195 ❘ 2003, Vol. 9, No. 2