Contents - Konrad Lorenz Institute

An Evolutionary Model of the Effects of Human Paternal Resemblance on Paternal Investment
risk for sperm competition by the female, otherwise
the male might be led to abuse, even infanticide, to
ensure that his resources were not spent on other
male’s offspring. Again, this is counter to the argument
put forth by BRESSAN and colleagues in which
they suggest that males would experience increased
fitness returns by not knowing paternity. This would
only be the case for those males chosen as EPC partners.
One could hypothesize that there is something
about males who engage in EPCs, who are selected as
EPC partners, or who adopt a primarily EPC-driven
reproductive strategy to produce anonymous looking
children. However, because the rates of EPP are
on the order of 1–20%, the majority of males in the
population would still require a means by which to
make assessment about paternity. It therefore is probably
more parsimonious to presume that females
choose EPC partners along two dimensions that help
to ensure investment from their in-pair partner. First,
females could choose to engage in EPCs with males
who resemble their in-pair mate, which would increase
the likelihood that the child might also bear
some resemblance to the in-pair mate. This would
also aid in maternal warping of the social mirror effect
(Gaulin, in press); i.e., if a female chooses an EPC
partner who resembles her in-pair partner, the in-pair
partner may be more susceptible to social affirmations
of resemblance. Second, because females usually
choose EPC partners that are more attractive,
symmetrical, and are presumed to have “better
genes” (see BAKER/BELLIS 1995, for a review), an inpair
mate might be more inclined to react favorably
towards a child that expresses “good genes” (e.g., being
more symmetrical). MEALEY (2003) recently demonstrated
that symmetry among twins did not account
for variation in treatment of the twins.
However, PLATEK et al. (in preparation), using a morphing
paradigm have documented significant differences
in reactions to children’s faces as a function of
symmetry, with more symmetrical faces eliciting
greater positive investment responses. Although the
effects of symmetry may play an important role in
child investment strategies, symmetry is not modeled
here.
Evidence for the Effects of Genetic
Relatedness and Paternal Resemblance
There is evidence that males differentially invest in
children to whom they are genetically related. It is
not uncommon for unrelated, or otherwise stepchildren
to be treated significantly worse than biological
children (e.g., ANDERSON et al. 1999). BURCH and
GALLUP (2000) have shown that the less a male
thinks a child looks like him, the worse he treats the
child, and the worse the relationship with that child
is. DALY and WILSON (1983; DALY/WILSON/WEG-
HORST 1982) have shown that male sexual jealousy
can become violent and can be interpreted as a
byproduct of the fear of infidelity, or possibility of
becoming a cuckold. They estimate the incidence of
abuse that results in infanticide among step-children
to be 100 times that of genetically related children.
These data suggest a strong link between perceived
resemblance, relatedness and the treatment
of children.
However, in terms of assessing resemblance, the
absence of mirrors during human evolution might
have precluded males from being able to objectively
determine the degree of facial resemblance. There
are several hypotheses about how and whether resemblance
could have had effects during our evolutionary
history. The first falls under a category that
has been referred to as the social mirror effect
(BURCH/GALLUP 2000). A social mirror consists of 1)
other people telling you that a child resembles you,
2) making comparisons between your child and
your putative genetic kin, and 3) monitoring behavioral
similarities, or lack thereof, between your offspring,
your kin, and yourself. There are data to support
the existence of a social mirror. It has been
shown that other’s perceptions of offspring-paternal
resemblance is important in 1) the father’s perceptions
of resemblance (DALY/WILSON 1983; REGAL-
SKI/GAULIN 1993) and 2) the degree of violent
behavior enacted by the father toward the offspring
and the mate (BURCH/GALLUP 2000, in press). Further,
DEBRUINE (2002) has shown that people trust
those who resemble them more than those who do
not, suggesting a role for kin-resemblance comparisons
(see also PLATEK et al. 2003).
However, although social mirror information
seems to be important for the ways in which a male
behaves toward a child, my colleagues and I have recently
found that, in hypothetical investment situations,
males react more positively toward faces of
children that actually share more of their own facial
features (PLATEK et al. 2002). This morphing study
employed stimulus faces that represented a 50%
morph; i.e., the stimulus child’s face was 50% child
and 50% subject. We have found that, in order for a
male to change from reacting indifferently to favorably
toward a child’s face they must share at least
25% facial characteristics in common with the
child’s face (PLATEK et al. 2003). This proportion of
shared characteristics parallels the degree of shared
Evolution and Cognition ❘ 191 ❘ 2003, Vol. 9, No. 2