KNOW ABOUT BIRTH ORDER AND RELATIONSHIPS
In order to understand the association between birth order and creativity, it is ﬁrst useful to review the relationship between birth order and personality, which owes itself to biological as well as environmental inﬂuences. Because there are no genes for being a ﬁrstborn or a laterborn, birth-order effects represent one of the best demonstrations of the power of the environment. Nevertheless, birth order interacts with other inﬂuences on human behavior, including genetic predispositions, that are known to be under biological control. Biological inﬂuences on personality may be separated into ultimate and proximate causes. Ultimate causes are those that are attributable to evolution by natural selection. By contrast, proximate causes encompass those physiological inﬂuences operating during the lifetime of the organism. Proximate causes also include environmental inﬂuences, which typically interact with genetic and physiological processes. Viewed in these terms, sibling rivalry provides an ultimate cause of some aspects of personality development. Darwin’s theory of natural selection offers an explanation for this part of the story, because it tells us that siblings are biologically driven to compete for parental favor. On average, siblings share half of their genes. In the early 1960s, William Hamilton recognized that natural selection acts to maximize what he termed ‘‘inclusive ﬁtness.’’ This form of Darwinian ﬁtness is deﬁned as an individual’s own reproductive success, together with his contribution to the reproductive success of close relatives, discounted according to their coefﬁcient of relatedness. Based on Hamilton’s theory, siblings are expected to compete for scarce resources whenever the beneﬁts of doing so are greater than twice the costs. In general, an offspring’s idea of fairness is to keep two-thirds of any scarce resource for himor herself and give only one-third to a sibling. Competition for parental investment is the main cause of sibling rivalry. By itself, competition among siblings does not lead to birth-order differences in personality. But birth order provides a powerful proximate (and environmental) source of sibling strategies. These tactical differences arise because birth order is correlated with differences in age, size, power, and status within the family. These physical and social disparities cause siblings to experience family relationships in dissimilar ways and to pursue differing ways of optimizing their parents’ investment in their welfare. Competition for parental love and favor has been an important driving force in human evolution, just as have parental decisions about how to invest in their offspring. Before 1800, half of all children did not survive childhood, and even minor differences in parental favor would have increased a child’s chances of reaching adulthood. Children who lived long enough to become the eldest in a family were often a better Darwinian bet for their parents, because they had survived the perilous years of life and were more likely than their younger brothers and sisters to reach the age of reproduction and to pass on their parents’ genes. In every society surveyed by anthropologists, eldest children are accorded higher status. For example, many traditional societies condone infanticide, especially when a child is deformed or when a slightly older infant is still breast-feeding, but no society condones the killing of the older of two siblings. Parental investment strategies tend to be variable because birth order is only one of many relevant factors in these decisions. Besides taking into account the relative quality of their offspring, parents may invest differently in children based on such factors as the parents’ age and the resources available to them. Primogeniture has generally been practiced by afﬂuent parents in agrarian societies, where wealth is tied to land; but this inheritance system is much less common in mercantile societies where wealth can be acquired rapidly through entrepreneurship. Under these conditions, parents tend to hedge their bets by investing equally in all of their offspring. Even if parents do not favor one child over another, sibling rivalry inﬂuences the dynamics of family life because competition serves to limit favoritism. Such competition typically involves the cultivation of family niches that correspond to differences in birth order. That families provide offspring with a series of niches is a conclusion supported by research in behavioral genetics. One of the most remarkable ﬁndings in psychology during the last two decades is the discovery that brothers and sisters raised together are almost as different in their personalities as people who grow up in separate families. Based on studies of twins raised together and apart, behavioral geneticists have concluded that only about 5% of the variance in individual personality traits is attributable to the shared environment — that is, growing up in the same family —whereas 35% can be assigned to the nonshared environment. About 40% of the overall variance is believed to be genetic, and the remaining 20% is attributable to errors of measurement. These ﬁndings have begun to reshape the understanding of personality development by suggesting that the family is not a single environment, but rather a collection of microenvironments or ‘‘niches.’’ The main reason why the shared family environment does not have a greater impact on personality is that very little of the family experience is actually shared. For example, brothers and sisters are at different ages when they experience the same events, and siblings often interpret shared experiences differently. Two particularly important and systematic sources of nonshared experiences are gender and birth order.
Psychologists have investigated the consequences of birth order ever since Charles Darwin’s cousin Francis Galton reported, in 1874, that eldest sons were overrepresented as members of the Royal Society. After breaking away from Sigmund Freud in 1910 to found a variant school of psychoanalysis, Alfred Adler highlighted social inﬂuences on personality, including birth order. A secondborn, Adler regarded ﬁrstborns as ‘‘power-hungry conservatives.’’ He characterized middleborns as competitive, and youngest children as spoiled and lazy. During the half-century since Adler’s speculations, psychologists have conducted more than 2,000 studies on the subject. This literature has often been faulted, and critics have rightly argued that the ﬁndings conﬂict and that most studies are inadequately controlled for social class, sibship size, and other background inﬂuences that correlate with birth order and can lead to false conclusions. The reality of these reported differences is nevertheless supported by meta-analysis — a technique for aggregating ﬁndings from different studies in order to increase statistical power and reliability. Considering those well-designed studies that adjust for social class or sibship size, meta-analysis reveals consistent birth-order differences for many personality traits. These ﬁndings may be summarized in terms of the Five Factor Model of personality. Controlled studies generally report that ﬁrstborns are more conscientious than laterborns, a difference that is exempliﬁed by their being more responsible, ambitious, organized, and academically successful. Laterborns appear to be more agreeable than ﬁrstborns, in the sense of being more tender-minded, accommodating, and altruistic. Laterborns are also more open to experience, as expressed by their being more adventurous and unconventional. Differences by birth order are more restricted for the two remaining dimensions of the Five Factor Model. Firstborns appear to be more neurotic than laterborns, in the sense of being temperamental and anxious about their status. In addition, ﬁrstborns are more extraverted than laterborns, in the sense of being assertive and dominant, whereas laterborns are more extraverted in the sense of being sociable and fun-loving. Dominance and sociability are substantially different personality traits, even though they are classiﬁed together within the Five Factor Model. Firstborns tend to have higher IQs than laterborns, but this difference is small, especially after being controlled for differences in family size. On average, IQ falls one point with each increase in birth rank within the family. (Proponents of the Five Factor Model consider IQ to be a sixth factor, largely independent of personality.) The personality differences that I have just reviewed are generally consistent with a Darwinian framework, albeit with an emphasis on adaptation through learning. Unlike the propensity to compete with one’s siblings, which is an ultimate cause of sibling conﬂicts, personality is a product of innumerable proximate causes that spur individuals to adapt themselves to the surrounding world. Firstborns often seek the favor of their parents by acting as a surrogate parent toward their younger siblings. As a result, ﬁrstborns tend to be parent-identiﬁed, conscientious, and respectful of authority. Laterborns cannot baby-sit themselves, so they look for an unoccupied family niche, in part by cultivating latent talents that can be discovered only through experimentation. For this reason, they are often more exploratory and open to experience. Another reason for the divergent personalities of siblings is the different strategies they employ in their relations with one another. These strategies involve behaviors that are typical of mammalian dominance hierarchies. Because ﬁrstborns are bigger, they are more likely to employ physical aggression and intimidation, and in general they are more likely to boss and dominate their younger brothers and sisters. Laterborns tend to use low-power strategies, such as whining, pleading, cajoling, humor, social intelligence, and, whenever expedient, appealing to parents for help. Two or more laterborns may also join in coalitions against the ﬁrstborn. A Darwinian approach also leads to speciﬁc predictions about middle children, who lack the advantages of being either ﬁrst or last. When resources are scarce, parents are expected to invest preferentially in ﬁrstborns because they are the ﬁrst to reproduce. Older parents are expected to invest preferentially in lastborns because these offspring are the most vulnerable to disease and, after parents have ceased reproducing, are the last children they will ever have. As Catherine Salmon and Martin Daly have shown, middle children often respond to their Darwinian handicap by becoming peer oriented and independent of the family. Compared with ﬁrstborns and lastborns, middle children are less closely identiﬁed with the family, less likely to turn to their parents for help in an emergency, and less likely to report having been loved during childhood. Compared with their siblings, middle children typically live farther away from their parents. In addition, they are the least likely sibling group to visit, and to encourage their own children to visit, close kin. Consistent with their greater allegiance to the peer group, middle children also are the most inclined to diplomacy and cooperation, strategies that may reﬂect their proclivity for mediating disputes between their siblings. Martin Luther King, Jr., the middle of three children, got his start as a champion of nonviolent reform by trying to prevent his younger brother from teasing their older sister. Only children represent a controlled experiment in birth-order research. Because they experience no sibling rivalry, they are not driven to occupy a speciﬁc family niche. Like other ﬁrstborns, they are generally ambitious and conform to parental authority, because these attributes are valued by parents. Contrary to psychological folklore, only children do not appear to be more neurotic or less sociable than other children. There is often a greater difference between a ﬁrstborn and a secondborn child, or between a secondborn and a thirdborn, than there is between the ﬁrstborn and the thirdborn. The reason is that sibling competition promotes mutual differentiation in order to minimize direct conﬂicts, and children who are farther apart in age have less need to compete. This process of sibling differentiation, which is sometimes called deidentiﬁcation, extends to relationships with parents. When a ﬁrstborn identiﬁes more strongly with one parent, the secondborn is likely to identify more strongly with the other parent. Some of these contrasts are striking. Voltaire, the third of three children, had an acrimonious relationship with his elder brother Armand, who became a follower of the Jansenists, a fanatical Catholic sect. Voltaire was particularly repelled by Armand’s belief in the need to forgo life’s pleasures in order to win God’s grace. As a leader of the French Enlightenment, Voltaire was especially noted for his relentless attacks on the Catholic Church. He chose literature as a profession partly to spite his brother, whom he had repeatedly bested in impromptu poetry contests devised by his family. A different example of sibling contrasts involves the consumer rights advocate Ralph Nader and his three older siblings. In early adolescence, the Nader children took a globe of the world, divided it into four equal portions, and assigned one part to each child. Thereafter, each specialized in the history, culture, and languages of his or her own quarter of the globe. By minimizing direct competition, the Naders were also cooperatively pooling their resources as a family unit, collectively enabling them to learn more about the world. As Darwin recognized in the Origin of Species (1859), diversiﬁcation is an effective way to reduce competition while also realizing the beneﬁts stemming from the division of labor.
Birth-order differences in personality vary in magnitude and sometimes even in direction, depending on how they are measured. When assessed by self-report questionnaires, birth-order effects are typically modest and nonsigniﬁcant. Yet systematic differences by birth order are generally found when parents rate their own offspring or when siblings compare themselves with one another. In a recent study by Frank Sulloway, 660 business leaders were surveyed. In self-reported ratings, ﬁrstborn CEOs did not differ signiﬁcantly from laterborns on 10 of the 11 personality traits included in the survey. After providing these self-assessments, respondents were asked to compare themselves with their siblings, using the same 11 personality scales. A comparative method of assessment possesses several advantages over more customary methods of selfreport. In particular, direct comparison anchors the scales. Additionally, comparative judgments among siblings eliminate any confounding effects associated with differences between families. Using such comparisons, 8 of the 11 traits included in the survey elicited signiﬁcant differences by birth order. Relative to their older siblings, laterborn business leaders were more tender-minded, cooperative, ﬂexible, submissive, empathetic, liberal, unconventional, and even-tempered. Overall, comparative ratings resulted in birth-order differences that were 5 times as large as those previously obtained without using direct comparisons. A follow-up study involving 6,053 individuals aged 8 to 95 (mean age 36.8, SD 17.1) has yielded similar results for a broad array of personality traits. Subjects rated themselves on nine-step bipolar scales using adjective pairs that were chosen to represent the 30 facets of the NEO PI-R, a comprehensive personality inventory based on the Five Factor Model. Firstborns were asked to rate both themselves and their next younger sibling, whereas laterborns were asked to rate themselves and their next older sibling. Based on direct sibling comparisons, 23 of the 30 bipolar adjective pairs yielded signiﬁcant differences, and 26 of the 30 adjective pairs produced correlations in the expected direction. As anticipated, ﬁrstborns were judged to be more conscientious than their younger siblings, whereas laterborns were judged as being more agreeable and open to experience. For neuroticism, a dimension for which birth-order differences were expected to be mixed, ﬁrstborns were predicted to be more anxious and quicker to anger — expectations that were both conﬁrmed. Laterborns were predicted to be more depressed, vulnerable, self-conscious, and impulsive, but only the last two predictions were conﬁrmed. As anticipated, results for extraversion were also mixed. Laterborns were more affectionate, fun-loving, and inclined to seek excitement. Firstborns were more energetic and dominant. Controlling for age, sex, sibship size, and social class, the partial correlation between birth order and a scale score of predicted differences was .20, with birth order accounting for 4.1% of the variance. Two other family background variables — sibship size and social class — account for less than 0.1% of the variance in this scale score of predicted differences, as also does age. By comparison, sex explains 2.1% of the variance. (Laterborn personality traits resemble those observed in females.) Controlled for the linear effect of birth order on the scale score, there was also a signiﬁcant quadratic trend: middle children scored higher than lastborns on some personality scales, particularly those related to agreeableness (Table I). Measured in terms of an overall scale score that reﬂects predictions about birth order, age and sex account for substantially less variance in personality scores than does birth order. It is important to note, however, that age and sex explain considerably more about personality as a whole than they do about birthorder-related traits. Sex differences in my study account for 8.3% of the variance in dimension scores for the Big Five, and age explains another 2.6% of the variance. In accounting for 4.1% of the variance in these same dimension scores, birth order is substantially more inﬂuential than age, but less so than sex. Still, on two dimensions of the Five Factor Model (conscientiousness and extraversion), birth order has greater inﬂuence than either age or sex. One should bear in mind that birth order is only a proxy for the real causes that lie behind sibling differences in personality, namely, disparities in age, size, status, and power within the family system. Not all ﬁrstborns adopt the role of a surrogate parent toward younger siblings, and some ﬁrstborns are less bossy than others. Individual differences in physical size, temperament, and opportunities for surrogate parenting help to explain why some individuals deviate from the patterns of personality that are generally expected by birth order. In the study summarized in Table I, individuals were asked to what extent, during childhood, they acted as a surrogate parent toward their siblings, and also to what extent they bossed their siblings around. High scores for surrogate parenting behavior and bossiness reﬂect typical ﬁrstborn behaviors and are strongly correlated with birth order (r .56 for the composite measure). This indicator of family niches also accounts for 10.5% of the variance in personality scores, making it considerably better at predicting personality than any other variable in the study. The predictive success of this variable lies in large part in its ability to account for exceptions to predictions based on birth order. For example, laterborns (often eldest daughters) sometimes report having done substantial surrogate parenting with respect to their younger siblings. These individuals also tend to describe themselves as having ﬁrstborn personality traits. Other studies using the NEO Personality Inventory and comparable instruments have generally yielded null results, although most of these studies have possessed only moderate statistical power and none have employed the method of direct sibling comparison. Based on similar discrepancies between self-report ratings, which often yield meager results, and signiﬁcant differences as judged by family members, some researchers have argued that birth-order effects are parent speciﬁc and do not hold up outside the family. When assessed meta-analytically, however, studies involving nonfamily members exhibit signiﬁcantly more ﬁndings of a conﬁrmatory nature than are expected by chance. Conﬁrmatory ﬁndings are also especially likely to occur whenever studies involve real-life behavior. In addition, if birth-order effects are speciﬁc only to childhood (and the family milieu), one might expect these differences to diminish with age. In the study reviewed in Table I, birth-order effects do decrease modestly with age for conscientiousness, but they increase modestly for agreeableness. Overall, there is not a signiﬁcant diminution in the scale score for predicted birthorder effects by age. The method of direct sibling comparison does not prove that birth-order differences in personality exist outside the family milieu. Direct sibling comparisons may also be susceptible to ‘‘contrast effects,’’ whereby small but real differences between siblings are magniﬁed, exaggerating the variance explained by birth order. However, when the scores in Table I for direct sibling comparisons are transformed into binary outcomes (i.e., being higher or lower than a sibling on each trait), birth-order effects are only slightly reduced. Another possibility is that these comparative measures reﬂect shared stereotypes about personality, rather than true differences. In an effort to determine whether birthorder differences are recognized by people other than siblings, study participants were asked to rate their spouses. Signiﬁcant birth-order differences emerged in the expected direction, although the mean effect size for the Big Five personality dimensions is somewhat smaller than for direct sibling comparisons. Controlling for age, sex, sibship size, and social class, the partial correlation among spouses between birth order and a scale score for predicted personality differences is .12, which accounts for 1.4% of the variance (N 822). An analysis of the scores for individual traits reveals that spouses are detecting the same birth-order differences that they reveal when they compare themselves with a sibling. A convenient way of demonstrating this point is to compare the effect sizes for birth order, on a trait-by-trait basis, with the effect sizes for the same traits as judged by spouses. These two sets of effect sizes are substantially correlated (r .61, N 30 traits, p .001). In other words, those traits that are strongly associated with birth order in sibling relationships are the same traits that are strongly associated with birth order in married couples. Relative to ﬁrstborn spouses, for example, laterborn spouses are perceived to be less conscientious, but more agreeable, extraverted, and open to experience. A similar pattern in birth-order effects is found among college students who rated both a sibling and a roommate (r .72, N 30 traits, p .001; for roommates, the partial correlation between birth order and a scale score for predicted personality traits is .16, N 165, p .05). Thus birth-order differences are not restricted to family members or the family milieu, as some psychologists have claimed. Rather, these differences tend to manifest themselves in intimate living situations.
Birth order exerts substantially more inﬂuence on behavior during radical revolutions than it does on self-reported personality traits, including those directly related to openness to experience. Radical revolutions typically constitute struggles over who controls valuable resources. It should come as no surprise that revolutionary challenges to the status quo provide a better test of personality differences (including those associated with birth order) than do self-report questionnaire data. In the study whose results are summarized in Table I, ﬁrstborns claimed to be signiﬁcantly more open to experience than their own younger siblings (d .16, equivalent to a correlation of .08). But laterborns claimed to be even more open to experience than their own older siblings (d .33, equivalent to a correlation of .16 in the opposite direction). The signiﬁcant net difference between these two correlations strongly suggests that laterborns are more open to experience than are ﬁrstborns, despite ﬁrstborns’ claims to the contrary. That the judgments of ﬁrstborns were generally incorrect about this aspect of their personalities is corroborated by their responses to an openended question. Subjects were asked, ‘‘What would your friends consider to be the two or three most unconventional or rebellious things, if any, that you have done during your life?’’ In answering this question, the number of words that respondents wrote down was signiﬁcantly correlated with their total score for openness to experience. Relative to ﬁrstborns, laterborns tended to produce longer responses and to list a higher proportion of truly unconventional behaviors, as assessed by independent judges. Other ﬁndings from this study reinforce the conclusion that social desirability inﬂuences self-reported judgments about personality. For example, older respondents believed that they were just as open to experience as younger respondents (r .00). Yet these same respondents claimed that their siblings and friends were signiﬁcantly less open to experience with age (meanweighted r .14). Both answers cannot be correct, and real-life evidence helps to arbitrate this issue. During radical revolutions, age is a reliable predictor of responses to change. As I have documented in a study of 121 major controversies in science and social thought, older individuals generally oppose radical changes (mean-weighted r .21, N 4,505). In my questionnaire study, people appear to have correctly recognized in others what they failed to acknowledge in themselves, namely, a reduction in open-mindedness with age. When we consider the fact that social desirability biases can produce correlational discrepancies as large as .3, and that most birth-order effects are about onethird this magnitude, it becomes more clear why selfreport data might tend to underestimate birth-order differences. On every dimension of the Big Five, social desirability effects dwarf those associated with birth order. Unfortunately, we cannot assume that such social desirability biases cancel themselves out with the use of direct sibling comparisons, because research has consistently shown that ﬁrstborns are more likely than laterborns to conform to social expectations. Because the degree to which self-ratings are embellished in a favorable direction is probably different for ﬁrstborns and laterborns, it is difﬁcult to know what is the true inﬂuence of birth order for any particular personality trait. For these reasons, real-life behavior remains the best test of the magnitude of birth-order differences in personality. Age and birth order are only two of many signiﬁcant predictors of individual responses to radical change. Being socially liberal is another substantial predictor. So is parent – offspring conﬂict, which disrupts birthorder effects among ﬁrstborns and makes them into ‘‘honorary laterborns’’ in terms of openness to experience. Multivariate models that include these and other predictors of openness to radical innovation are signiﬁcantly more powerful than predictions based on single variables. In general, people who are the most likely to endorse radical changes are also more likely than average to initiate such changes. Hence a willingness to endorse heterodox viewpoints is a necessary, but by no means a sufﬁcient, condition for intellectual discovery. These ﬁndings do not mean that young people, laterborns, and social liberals have a monopoly on scientiﬁc creativity or truth. For example, laterborns run the risk of accepting new and radical viewpoints too quickly, just as ﬁrstborns run the risk of resisting certain kinds of necessary changes. Laterborns were nine times more likely than ﬁrstborns to support Franz Joseph Gall’s false theory of phrenology — the notion that character can be read by tracing bumps on the head. Firstborns correctly rejected this theory as pseudoscientiﬁc. (They also disdained phrenology because of its materialistic implications.) During everyday ‘‘normal’’ science, ﬁrstborns have a small but consistent advantage over laterborns. They are more successful academically and are more likely to become scientists in the ﬁrst place. In addition, ﬁrstborns tend to win more Nobel prizes, which are generally awarded for creative puzzle solving (openness in the sense of ‘‘intellect’’) rather than for revolutionary innovations (openness in the sense of ‘‘nonconformity’’). Einstein revolutionized physics with his theories of special and general relativity. The Nobel Prize committee was wary of these theories and honored him instead for his discovery of the photoelectric effect. Owing to publication of the Origin of Species, Charles Darwin lost a knighthood that he had previously been slated to receive. A good indicator of a radical scientiﬁc revolution is the widespread opprobrium, not the accolades, that initially befall the instigators. When scientiﬁc innovations involve ideologically conservative implications — as occurred, for example, with vitalistic doctrines during the 17th and 18th centuries — ﬁrstborns possess an even greater intellectual advantage over laterborns than they do during ‘‘normal’’ science. Historically, ﬁrstborns have repeatedly championed new theories that bolstered God’s role in the Creation. Assessed jointly in terms of birth order and the ideological implications of innovations, four classes of innovation are possible, but only two have ever been documented. For example, laterborns have generally led radical revolutions, such as Copernicanism and Darwinism, that strongly challenged social and religious authority. Firstborns have generally backed innovations, such as eugenics and spiritualism, that also appealed strongly to religious and political conservatives. By contrast, there has never been an instance of a ﬁrstborn-backed radical revolution; nor has there ever been a case of a conservative revolution that was advocated by laterborns and opposed by ﬁrstborns. In sum, the relevance of birth order to scientiﬁc innovation is strongly dependent on the nature of the innovation.
Controlled for social class and sibship size, ﬁrstborns are overrepresented as scientists. Among laterborn scientists, middle children are particularly underrepresented, as they are among eminent individuals. These ﬁndings accord with the evidence that ﬁrstborns are more conscientious than laterborns, and that parents, especially under conditions of limited resources, tend to invest preferentially in ﬁrstborns and lastborns. On closer examination, evidence from the history of science indicates that ﬁrstborns and laterborns tend to achieve eminence in dissimilar ways. Firstborns have generally excelled in the physical sciences, where intellectual problems tend to be more clearly deﬁned than in the life sciences. By contrast, laterborns have gravitated toward the biological and social sciences, where success often depends on knowing what the most important problems really are. The scientiﬁc achievements of laterborns have been facilitated by their tendency to pursue multiple research interests, a strategy that has been particularly fruitful within the life sciences where unsolved problems often transcend disciplinary boundaries. Charles Darwin distinguished himself in geographic exploration, geology, zoology, botany, ethology, and psychology. His knowledge of these diverse disciplines was crucial to his ability to develop his theory of evolution by natural selection. Laterborns often achieve distinction in those walks of life that allow expression of their tender-minded qualities. For instance, laterborns are overrepresented among winners of the Nobel prize in literature and peace. Among participants in the abolition and Black Rights movements —who were mostly laterborns — middle children were the most likely group to employ nonviolent methods of persuasion. By contrast, ﬁrstborns and lastborns advocated militant strategies. During the French Revolution, ﬁrstborns such as Maximilien Robespierre rose to power within the National Convention by supporting the Reign of Terror. Younger siblings (particularly middleborns such as Georges Jacques Danton) opposed these extreme political measures and were ultimately responsible for the overthrow of Robespierre’s Montagnard (and largely ﬁrstborn) political party. The relationship between birth order and creative achievement has not yet been studied with sufﬁcient rigor for many intellectual domains, including music, art, literature, and business. When undertaking such future studies, researchers should bear in mind the differing kinds of openness to experience and their potentially distinct relationships with birth order. Studies also need to be controlled for other covariates —especially sibship size, social class, parent – offspring conﬂict, and social attitudes — that are required either for methodological reasons or because these variables moderate the inﬂuence of birth order. Ordinal position is only a proxy for differences in family niches (such as acting as a surrogate parent), and these proximate – causal mechanisms of personality development need to be investigated in greater detail. Finally, the nature of the behavioral situation is often a powerful moderating variable. In radical revolutions, birth-order effects tend to fade over time, as new and initially controversial ideas become more widely accepted. In addition, some new ideas are more controversial than others and tend to elicit correspondingly larger birth-order effects. National differences sometimes mediate these effects. Given their allegiance to Descartes’ rival theory of celestial mechanics, French physicists — especially ﬁrstborns — manifested strong opposition to Isaac Newton’s theory of universal gravitation. British scientists, including ﬁrstborns, welcomed Newton’s ideas. Ultimately, the relationship between birth order and creativity needs to be approached in meta-analytic terms that include explicit roles for the nature of the innovation, as well as the social and intellectual contexts in which such innovations arise.
Birth order provides one important source of personality differences, which in turn underlie differences in creative achievement. Disparities in birth order cause siblings to experience the family environment in dissimilar ways. In addition, birth order introduces the need for differing strategies in dealing with sibling rivals as part of the universal quest for parental favor. This is a Darwinian story, albeit with a predominantly environmental twist. Siblings appear to be hardwired to compete for parental favor, but the particular strategies they adopt within their own family are determined by the speciﬁc niche in which they have grown up. As children become older and leave the family, they modify their behavioral strategies — both competitive and cooperative — as they adapt themselves to new life roles. The enduring imprint of childhood learning, and its manifestations in adult personality, is nevertheless discernible in those abilities that come to us most naturally and that owe themselves to prior niche partitioning within the family. Through its context-sensitive relationship with birth order, creative achievement represents a case in point. Evidence from intellectual and social history highlights the conclusion that ﬁrstborns and laterborns do not differ in overall levels of creativity. Rather, brothers and sisters are preadapted to solving disparate kinds of problems, which they generally tackle using differing kinds of creative strategies.