Our results reveal a gender bias in the intuitive heuristics voters use when evaluating political candidates and deciding who to vote for. Voters perceive the faces of male politicians as more competent and dominant relative to female politicians whereas female politicians are perceived as more attractive and approachable relative to male politicians. Given the known importance of facial inferences of competence in predicting actual electoral outcomes 
, this finding suggests that one factor underlying the political gender gap is the impression that voters have of male politicians as more competent than female politicians.
Why do the faces of male politicians signal greater competence and dominance to voters relative to the faces of female politicians who appear more attractive and affiliative? One possible explanation posited by thin slice theory 
is that voters are able to accurately infer the actual competence of politicians solely from facial appearance and thus, in this study, voters accurately glean from facial appearance that male politicians really are more competent relative to female politicians. However, this explanation is unlikely for two reasons. First, meta-analytic evidence indicates that female and male leaders do not differ in actual effectiveness or competence across a range of leadership roles (e.g., managers to CEOs), irrespective of their preferred leadership style (e.g., transformational vs. transactional) 
. Second, empirical work examining the effectiveness of governments led by women has shown that female politicians outperform male politicians in several ways 
. For instance, female politicians in India are less likely to be corrupt and more likely to provide public goods in a fair and affordable manner relative to their male counterparts 
. Although the effectiveness of male and female politicians is difficult to wholly examine due to the persistent lack of representation of female politicians in the highest echelons of modern government, a growing body of evidence indicates that male and female politicians do not differ in actual leadership effectiveness.
An alternative explanation based on social role theory is that voters construe positions of top political leadership, such as the President of the United States, as inherently more masculine in nature (e.g., requiring the ability to direct and control others) and thus, perceive faces of male politicians, which contain more masculine facial features, as more competent or effective in that political role relative to faces of female politicians, which contain more feminine facial attributes. Conversely, because faces that contain feminine or baby-faced facial features are perceived as more attractive and affiliative, voters perceive female politicians as significantly more attractive and affiliative relative to male politicians. Given the evidence showing that men and women do not differ in leadership effectiveness, we suggest that voters' perception of male politicians as more competent relative to female politicians observed in the current study are more likely driven by cultural stereotypes of who is more likely to be competent rather than accurate assessments of who is actually competent.
The present findings further indicate that gender stereotypes predispose us to value divergent qualities in leaders, such as attractiveness in female politicians and approachability in male politicians, when deciding whom to vote for in major elections. Although impressions of competence from facial appearance are ubiquitously predictive of voting behavior, both male and female voters are more likely to vote for female politicians who not only appear competent, but also attractive. Moreover, female voters are more likely to vote for male politicians who not only appear competent, but also approachable. These results corroborate a growing body of research demonstrate the potency of facial appearance in political decision-making 
and highlight the gender bias in intuitive heuristics used by voters when evaluating the faces of male and female political candidates and deciding who to vote for.
Why does facial attractiveness matter to the electoral success of female but not male politicians? One possible explanation is that the current findings are simply a result of experimental task demand. That is, because voters judged female politicians as more attractive relative to male politicians prior to the voting phase of the experiment, they valued attractiveness in female politicians to a greater extent relative to male politicians and were more likely to vote for attractive female politicians relative to attractive male politicians. However, this explanation is not likely for two reasons. If voters' facial judgments of attractiveness influenced their voting behavior for female and male politicians, then their voting behavior should have been similarly affected by the other kinds of facial judgments, including competence, dominance and approachability made prior to the voting phase of the current study. As discussed earlier, all voters judged male politicians as appearing more competent relative to female politicians; yet, competence was equally predictive of voting behavior for both male and female political candidates. Similarly, all voters judged male politicians as appearing more dominant relative to female politicians; however, perceived facial dominance was not predictive of voting behavior for either female or male political candidates. Hence, it is not likely that our findings are solely a function of task demand.
Another possible explanation based on the ‘halo effect’ is the notion that voters perceive attractive female politicians as good at leadership because of a cognitive bias to unconsciously associate attractiveness with superior ability in other, unrelated personality dimensions, such as intelligence, talent, kindness and honesty 
. However, the ‘halo effect’ cannot explain why in the current study facial attractiveness was associated with voting for female but not male politicians.
A third, more nuanced, explanation of the current findings based on evolutionary theory is that people automatically evaluate faces using a core constellation of intuitive heuristics critical for other kinds of adaptive decision-making, such as mate selection. Akin to leadership selection, men and women value different qualities in heterosexual mate selection. Across cultures, men are more likely to prefer women who are physically attractive, whereas women are more like to prefer men who have high social status or demonstrate the ability to garner resources 
. We suggest that both male and female voters value physical attractiveness in female but not male politicians because this adaptive quality is emphasized in mate selection and thus engenders a broader cultural expectation that attractive women are more deserving of high social status roles not only in the domain of sexual selection, but also leadership selection. Similarly, female voters value not only competence but also approachability in male politicians due to the importance of qualities such as kindness and warmth in female selection of male long-term partners 
Our findings also indicate that voters in the current study showed similar, though not identical, preferences to people who voted in the actual 2006 House of Representatives election. Margin of victory for politicians in the hypothetical Presidential election was associated with margin of victory in the actual 2006 House of Representatives election, suggesting that voter preferences observed here generalize to preferences of the general electorate across different kinds of political offices. Additionally, candidates who were perceived as more attractive by men were more likely to win votes in the actual Congressional election. However, there were notable distinctions in the relationship between gender, facial inference and voting behavior in current simulated Presidential election outcomes versus actual Congressional election outcomes. First, candidates who were perceived as competent were less likely to win the actual Congressional election, whereas candidates who appeared dominant were more likely to win votes in the actual Congressional election. Second, none of the facial inferences that predicted simulated voting for female Presidential candidates were predictive of their actual Congressional outcomes. One possible explanation for this discrepancy between the intuitive heuristics that predict simulated Presidential voting in the current experiment and actual Congressional outcomes is that there is a fundamental difference in voter preferences in the laboratory settings relative to in real elections. However, this explanation is not likely due to prior research showing that facial inferences made laboratory settings predict actual election outcomes 
Another possibility is that the intuitive heuristics used by voters during leader selection varies as a function of the prestige and selectivity of the political office. We suggest that this alternative explanation is more likely given that the degree of selectivity required in choosing a leader for the highest political office (e.g., one leader instead of one out of several leaders at the same rank) is more analogous to the degree of selectivity required when choosing a mate and thus, gender biases evident in mate selection may exert greater influence in leader selection, particularly under these circumstances. For instance, while political gender gaps exist throughout the political ladder, they are most visible in the very highest echelons of governments around the world. Over 40 women ran for office in the 2006 U.S. House of Representatives election alone, whereas not once has there been a female major party candidate for President in U.S. history.
In sum, here we identify two psychological attributes of the voter that likely contribute to the political gender gap. First, gender stereotypes may bias voters to value male politicians over female politicians simply because they possess facial features that signal qualities associated with effective leaders. Second, endowed with intuitive heuristics for selecting optimal mates, voters may unconsciously apply this set of core heuristics when making other kinds of seemingly unrelated, but important, social decisions, such as deciding whom to vote for. While the ideal personal characteristics of a good political leader at first glance appear largely distinct from those that comprise a good mate, cognitive remnants of our evolutionary history may predispose us with similar gender biases, which are incongruent with modern cultural ideals of gender equality in political representation and political power.
Notably, exposure to female politicians has been shown to reduce use of gender stereotypes when evaluating leadership effectiveness as well as overall negative biases towards female leaders 
. While the current findings demonstrate gender biases in facial inferences that affect voting behavior, as women become an increasingly visible presence in electoral politics and government, voters may learn to reduce their reliance on cognitive shortcuts, such as gender stereotypes and intuitive heuristics