1. Introduction

Optimal allocation of reproductive effort to either parenting or mating is contingent upon variables that affect the fitness returns for either type of effort (Hurtado & Hill, 1992, Maynard Smith, 1977). The genetic relatedness between parent and offspring most obviously influences the fitness returns for parenting. Indeed, a number of studies have reported that men care for and invest less in their stepchildren than for their genetic children (Anderson et al., 1999a, Anderson et al., 1999b, Flinn, 1988, Marlowe, 1999). This parental discrimination is also reflected in crime statistics against children. Children living in stepfamilies are much more likely to be both physically abused and killed, as compared with children living with their biological families (Daly & Wilson, 1988a, Daly & Wilson, 1988b). These are circumstances in which it is obvious that the child is not genetically related to the male.

Because men are never fully certain of their paternity, they may need to rely on cues to assess it. Wilson and Daly (1992) proposed that a male's estimation of the degree of phenotypic resemblance between himself and his offspring may be one possible cue to his paternity. Studies have found that Canadian, Mexican, and U.S. mothers that have just given birth allege paternal resemblance much more than maternal resemblance (Daly & Wilson, 1982, Regalski & Gaulin, 1993). Even more, the bias in paternal resemblance is exaggerated while mothers are in the presence of the father (McLain, Setters, Moulton, & Pratt, 2000), suggesting an evolved strategy on the part of females to increase men's paternity confidence and, presumably, thereby increasing paternal investment (Daly & Wilson, 1982, McLain et al., 2000).

There is some evidence that resemblance may be related to investment. When asked to make hypothetical investment decisions, some studies found that males react more favorably towards children whose faces are morphed to resemble their own faces (Platek et al., 2002, Platek et al., 2003). This study will examine whether men's perceived resemblance to their offspring predicts their reported parental investment.

Another possible cue to paternity confidence may be a male's perception of his mate's fidelity. Significant sex differences in the valuation of chastity have been found across cultures, with males valuing it more than females do (Buss, 1989) and desiring characteristics, such as faithfulness and sexual loyalty, as extremely important in a long-term mate (Buss & Schmitt, 1993; but see Buckmaster, Nell, & Jankowiak, 2002, on female mate guarding). This suggests that men look for cues that predict future sexual conduct when choosing a long-term mate and prefer characteristics such as faithfulness and chastity to ensure future paternity (Buss & Schmitt, 1993). Accordingly, a male's estimation of his mate's fidelity may also be a cue to his paternity. This study also examines whether men's perception of the fidelity of their children's mother predicts their reported parental investment.

Some parenting effort may actually be a form of mating effort (van Schaik & Paul, 1996, Smuts & Gubernick, 1992). This study therefore also examines the effects of paternal resemblance and mate fidelity on reported parental investment in men who are in a relationship with the mother of their children and those who are no longer in a relationship with the mother of their children because it is unlikely that men engage in mating effort with former mates.

2. Methods

The participants in this study were 170 adult males recruited by one of the authors (Apicella). About 75% of the men were recruited from London's Heathrow Airport and a major train/subway station in London. The researcher attempted to approach all men who were alone and appeared old enough to be a father. Men who were first noticed by the researcher were approached first. Men who appeared overly busy or on a cell phone were not approached. However, because the researcher generally stayed in the same areas while recruiting, individuals who appeared less busy at a later time were subsequently approached. Only men who reported that they had biological children were asked to complete the anonymous survey. Both travellers and workers at the airport/train station were recruited for participation. The rest of the men were recruited from the general public around Northampton, England. Four individuals refused to complete the questionnaire.

Fathers were asked to respond to a number of statements using five-point Likert scales ranging from strongly agree to strongly disagree. Points for each item were summed together to obtain a single score for each independent and dependent measure. The amount of perceived resemblance between a father and his offspring was measured by men's responses to the following statements: “I believe that my child looks more like me than its mother,” “I think my child shares similar personality traits with me,” and “Most people think my child looks like me.” A coefficient of reliability of .79 (Cronbach's α) was obtained for these three measures of resemblance. Men's perception of the fidelity of the mother of their children was measured by their responses to the following statements: “The mother of my child is/was trustworthy,” “I believe the mother of my child is/was faithful to me,” and “The mother of my child dresses in revealing clothing.” The last statement was reverse scored. A Cronbach's α of .61 was obtained for these three measures. Finally, the following statements were designed to measure men's investment: “I believe I give my child a lot of attention,” “I spend a lot of time with my child,” and “I am/was involved with my child's schoolwork.” A Cronbach's α of .83 was obtained for these three measures of investment.

Multiple regression analyses were employed to examine the combined effects of perceived mate fidelity and perceived resemblance on men's reported investment. In all regressions, we controlled for the child's age and sex and the father's relationship status (whether he is still with the child's mother), ethnicity, total number of children, and number of hours worked per week (Table 1). We do not have coresidence data but assume that it is highly correlated with the age of the child and whether men are in a relationship with the mother of their children. Income was not included in the regression analyses because only 77.6% of men reported their annual income and we wanted to use our whole sample in the analyses. However, we ran separate analyses and found that income did not influence investment nor did it affect the significance of our predictors.

Table 1. Summary statistics of all variables used in the analyses, by relationship status

		Entire sample	In a relationship (77.6%)	Not in a relationship (22.4%)
	Age of child*	M=12.32	M=11.53	M=15.05
		S.D.=7.31	S.D.=7.24	S.D.=6.96
		n=170	n=132	n=38
	Sex of child	Male (51.5%)	Male (49.6%)	Male (57.9%)
		Female (48.5%)	Female (50.4%)	Female (42.1%)
	Ethnicity: White (W), Black (B), and Asian (A)	W (92.9%)	W (92.4%)	W (94.7%)
		B (2.9%)	B (3%)	B (2.6%)
		A (4.5%)	A (4.5%)	A (2.6%)
	Number of children	M=2.07	M=2.10	M=1.97
		S.D.=1.07	S.D.=1.10	S.D.=0.97
		n=170	n=132	n=38
	Hours worked per week	Median=47.58	Median=48.07	Median=45.94
	Resemblance*	M=9.98	M=10.27	M=8.97
		S.D.=2.64	S.D.=2.59	S.D.=2.58
		n=167	n=129	n=38
	Fidelity**	M=12.43	M=13.10	M=10.11
		S.D.=2.17	S.D.=1.44	S.D.=2.64
		n=170	n=132	n=38
	Investment**	M=10.09	M=10.56	M=8.67
		S.D.=2.75	S.D.=2.56	S.D.=2.81
		n=144	n=108	n=36

* Significant difference between separated men and men in a relationship, p<.05. ** Significant difference between separated men and men in a relationship, p<.005.

3. Results

Overall, men who are in a relationship with the mother of their children report significantly higher levels of investment compared with men who are no longer in a relationship with the mother of their children (Table 1; z=−3.56; p<.0005, equal variances not assumed). Furthermore, men no longer in a relationship with the mother of their children reported lower fidelity in the mother as compared with men still in a relationship with the mother of their children (z=−6.41; p<.0005, equal variances not assumed).

For the sample as a whole, the various independent variables together explained nearly 25% of the variance in paternal investment (Table 2, Column 1). Men reported greater investment in children if they perceived them as having greater resemblance to themselves (β=.285, p<.0005). Men also reported greater investment in children when they perceived their children's mother as having greater fidelity (β=.278, p=.004).

Table 2. Multiple regression model with investment as the independent variable

	Variable	Entire sample			In a relationship			Not in a relationship
		β		p	β		p	β		p
	Age of child	−.076		.315	−.097		.292	.002		.989
	Sex of child (♂=1 ; ♀=2)	.206		.007	.223		.017	−.096		.545
	Relationship status (separated=1; in a relationship=2)	.061		.513	–			–
	Black	−.055		.468	.005		.960	−.143		.353
	Asian	−.108		.157	−.106		.255	−.232		.105
	Number of children	.015		.846	.029		.744	.166		.288
	Number of hours worked	−.080		.292	−.181		.051	.394		.018
	Resemblance	.285		.000	.201		.034	.709		.000
	Fidelity	.278		.004	.322		.001	.158		.266
	Adjusted R2		.248			.191			.405
	F		6.135			4.07			3.98
	p		.000			.000			.003

For men still in a relationship with the mother of their children, we were able to explain just over 19% of the variance in paternal investment (Table 2, Column 2). Greater paternal investment was reported if greater resemblance (β=.201, p=.034) and greater fidelity were reported (β=.322, p=.001). For men who reported being separated or divorced from the mother of their children, the independent variables explained just over 40% of the variance in paternal investment (Table 2, Column 3). For this group, greater resemblance predicted paternal investment (β=.709, p<.0005), while greater mate fidelity did not (β=.158, p=.266).

4. Discussion

This study examined whether perceived paternal resemblance and mate fidelity, two possible cues to paternity, predict parental investment in men. We have found that as men's paternal resemblance and mate fidelity increases, so does their reported parental investment. However, among men who were no longer in a relationship with the mother of their children and thus less likely to be investing in mating effort with them, we found that paternal resemblance became a stronger predictor of investment, while mate fidelity no longer predicted investment. When we examined the differences in perception of mate fidelity between men in a relationship with the mother of their children, compared with those who are separated from her, we found that it was significantly lower for the latter. This finding suggests that a male's perception of the mother's fidelity could be redefined during or after the breakup of a relationship. It is also possible that lower mate fidelity could have caused the breakup. Either way, it seems that when fidelity is in doubt, men should rely more heavily on other cues, such as resemblance, to estimate their paternity for each child independently.

Men in a relationship with the mother of their children reported higher levels of parental investment as compared with men who were no longer in a relationship. This is consistent with other findings that men invest more in their genetic children from their current mates as opposed to their genetic children from their former mates (Amato, 1987, Anderson et al., 1999b, Weiss & Willis, 1985, Weiss & Willis, 1993).

This study used men's current perceptions of their mates' fidelity as a possible cue to paternity. It is important to note that this may not be as useful a measure for paternity as men's perception of their mate's fidelity at the time the child was conceived. Despite this, we do believe that this is still a useful measure. Not only are men's perceptions of their mate's fidelity influenced by their mate's past behaviors, but men may also be able to reassess their paternity by using cues long after the conception of the child. For instance, a man may believe that his mate was faithful at the time of conception, but her later infidelities could cause the male to reconsider his earlier assessment.

Perceived paternal resemblance predicted parental investment in men, but from an evolutionary perspective, we must ask how men in the past could gauge their resemblance to their offspring. Modern men are continuously exposed to images of themselves through mirrors, pictures, and even videos and, therefore, are likely to have a well-developed visual template of “self-image” for estimating paternity. It is quite possible that ancestral males had a similar template of self-image, albeit not as detailed and extensive as modern males do. Although a man's own face was largely inaccessible to ancestral males, except for occasional glimpses of reflections in water, the rest of the body was accessible. Nonvisual cues of self, such as personality, behavioral traits, and smell, were also available. In addition, a male could also use his mother's and siblings' faces as templates because mothers share 50% of their genes with their offspring, and siblings share at least 25% of their genes, on average, with one another. Using a brother as a visual template for assessing paternity would be useful so long as the brother is not actually the father of the child in question.

This study provides preliminary evidence that men may be responding to changes in paternity confidence by varying their levels of parental investment. Our findings are consistent with the findings reported by Fox and Bruce (2001) that paternity confidence, measured by how often fathers wonder if their children are really their genetic offspring and whether they looked for certain things about their children to verify this, predicts the degree to which a child is loved and wanted by his father in a sample of men from Tennessee. Other factors in addition to paternity confidence, such as father effect on offspring quality and survivability (Blurton Jones et al., 2000, Maynard Smith, 1977) and men's chances of gaining additional mates, also influence men's investment and, therefore, should be examined in relation to paternity confidence. Finally, further progress is needed in the development of more suitable measures of paternity confidence.