Contents - Konrad Lorenz Institute

Steven M. Platek
“plunge” the vagina of another male’s sperm (see
GALLUP et al. 2003). GALLUP et al. (2003, under review)
and GOETZ, SHACKELFORD and colleagues (in
press) have demonstrated that males behave differently
under conditions of possible sperm competition
that would maximize the capacity for using
their penis to displace another male’s semen. Both
papers report that under conditions of risk for
sperm competition males experienced thrusting
deeper, faster, and more vigorously, which would
serve as an advantage for semen displacement.
The final defense against cuckoldry is to assess paternity
of the child post-parturition. There has been
speculation that males do this by assessing the degree
to which children share resemblance with him
and there is evidence that this strategy is used in humans
and perhaps also other species (see e.g., PLATEK
et al. 2002, 2003; PLATEK 2002; WESTNEAT/SHERMAN
1997; SHERMAN/MORTON 1988). Phenotypic cues
may provide evidence about a man’s actual genetic
relatedness to his putative offspring. These cues
would, of course, concern physical resemblance
(Gaulin, personal communication).
BRESSAN and colleagues (BRESSAN/DAL MARTELLO
2002; see also PAGEL 1997) have suggested that
males would benefit from his children expressing
genes for anonymity of paternity as opposed to paternal
resemblance, but this model is not supported
by data from several studies (see PLATEK, et al. 2002,
PLATEK et al. in press, PLATEK/GALLUP under review).
In addition, BRESSAN et al.’s model makes little sense
from an evolutionary perspective in which determination
of paternity is a critical task for males. Selection
for anonymous looking children makes little
sense bearing in mind the basic principles of inheritance.
The only way in which BRESSAN’s anonymity
model might be accurate is if the rate of cuckoldry
(i.e., EPP) was 50% or greater. However, confirming
earlier reports (MACINTYRE/SOOMAN 1991), recent
studies using DNA fingerprinting have shown that
the incidence of EPP ranges from 1–20% (CERDA-
FLORES et al. 1999; SASSE, MÜLLER, CHAKRABORTY/OTT
1994; SYKES/IRVEN 2000). These studies support the
idea that there is (and was during human evolutionary
history) a substantial risk for EPP as a result of
females engaging in EPCs, and males who were selected
for detecting EPP would have left more descendants
that shared genes in common with them.
Following I attempt to model the way in which paternal
resemblance might affect a male’s decision to
invest resources in children.
GEARY (1999) has outlined a theory of paternal investment
based on psychosocial–evolutionary strategies.
He suggests that paternal investment should
only have evolved if it provided some benefit (increases
in survival rate of children, quality of child,
etc.) to the child (and, by virtue of genetic relatedness,
to the parent). Otherwise selection would have
favored an abandonment strategy which would allow
males the opportunity to engage in additional
reproductive opportunities. GEARY emphasizes the
importance of paternal presence in the development
of offspring, which might have longer-term
fitness consequences (see GEARY 1999). For example,
children without investing fathers often exhibit
subtle social incompetencies, and in the most extreme
case may not survive (e.g., because of malnutrition
or murder by a resentful stepfather). Therefore,
it seems that paternal investment provides
relative, not absolute benefit to the child and
should result in a mixed reproductive strategy
(GEARY 1999). In other words, there should be a
large degree of individual variation in investment
behaviors as a result of weighing the costs of investment
against the costs of losing reproductive opportunities
by investing in offspring that may not share
genes in common. The costs of investment can be
minimized if the male had a mechanism by which
he could determine that he is the source of paternity.
That is, if the male determines with relative,
probabilistic confidence that he is the genetic father,
the costs of lost reproductive opportunities are
significantly lessened or outweighed if his investment
in the child affords him increased fitness with
increased long-term fitness advantages; i.e., as a
function of the father’s investment, the child might
develop certain social competencies that afford the
child increased reproductive opportunities in the
future, enhancing the male’s fitness as a consequence.
If the male is uncertain about paternity, then
abandonment should have been favored by selection.
Additionally, a male could choose to stay with
the female (e.g., taking on a wife and step-child) in
the interest of mating effort (ANDERSON/KAPLAN/
LANCASTER 1999). Abandonment, however, might
allow the male to engage in alternative reproductive
opportunities without the cost of investing valuable
resources on another man’s offspring.
GEARY’s model also suggests that selection would
have favored investment when there were few alternative
reproductive opportunities, which might account
for a male taking on a mate and a step-child in
the interest of additional mating opportunities . I
suggest that this would only happen to the extent
that the male had confidence that he would not be at
Evolution and Cognition ❘ 190 ❘ 2003, Vol. 9, No. 2