MATE SELECTION
65
twice as many husbands of MZ twins looked approvingly,
rather than disapprovingly, on their fiancee’s cotwin, may re-
flect the well-established finding that, in many different cul-
tures, men attach relatively more importance than women do
to physical appearance (Buss, 1989). These husbands presum-
ably found their fiancees to be physically attractive; their
fiancee’s MZ cotwins would have tended to have a very similar
physical appearance and therefore would have tended to be
seen as similarly attractive. Even for the husbands, however, one
fourth of them actually disliked the MZ cotwin of the individ-
ual they had recently selected as their mate, and only 13% en-
dorsed could have fallen for her myself Among wives of male
MZ twins, in contrast, an equal proportion say they disliked as
liked their prospective twin brother-in-law
The second marked difference in Table 5 is that significantly
more of the spouses of DZ twins, of both sexes, reported that
they disliked than liked their spouse-to-be’s twin. Among wives
of DZ male twins, for example, twice as many disliked as liked
their prospective twin brothers-in-law, whereas, among female
DZ twins (Table 4), equal proportions liked as disliked their
prospective (nontwin) brothers-in-law. We see no obvious expla-
nation for this curious difference; why should a young woman
tend to feel more antagonistic toward her husband’s brother
than she feels toward her sister’s husband?
It is plain, however, that the results in Table 5, like those in
Table 4, confirm the similarity of MZ twins in much of their
important choice behavior although, at the same time, provid-
ing little evidence for the lawfulness of mate selection among
singletons. When MZ twins rated their cotwin’s selections (Ta-
ble 4), 39% liked them, but 38% disliked them; only 5% said
they could have fallen for (him/her) myself whereas 9% insisted
that they would have rather stayed single than marry their CO-
twin’s choice. When singletons rated the charms of their
spouse’s MZ twin-as they perceived them at the time when
they had decided to marry the cotwin-39% said they liked,
but 30% said they disliked, their fiance’s or fiancee’s twin; only
10% said they could have fallen for their spouse-to-be’s identical
twin (13% of the husbands and 7% of the wives), whereas 7% of
both sexes would have rather stayed single.
General Discussion
To summarize the argument thus far, for those of us who are
free to make a choice, mate selection is often the most impor-
tant choice we make. That most human choice behavior is law-
ful, rather than capricious, would not seem to require empirical
proof; the fact that, by their own report and the report of their
spouses, twins tend to make similar choices of friends, clothes,
vacations, jobs, and so on, with MZ twins more similar than
DZ twins, might therefore be regarded more as a confirmation
of the twin method for studying choice behavior than as proof
of the obvious, namely, that most choices tend to be determined
by the genetic and learned characteristics of the chooser. It is
therefore reasonable to use the twin method to investigate what
characteristics of the chooser and chosen determine the choice
of a mate.
Because spouses tend to resemble one another in most re-
spects, and especially in age, traditionalism, physical attractive-
ness, education, and perhaps in “mate value” generally, it might
be supposed that similarity is the key-that one chooses as a
mate that candidate who is most similar to one’s self. There is
no direct evidence for this conclusion, however. The observed
spousal correlations would result if we did no more than avoid
mating with the 50% of the population who are least similar to
ourselves. Moreover, it seems probable that much of the ob-
served pattern of spousal correlation might result from natural
social stratification limiting most of our circle of acquaintances
to people who fall within this 50% similarity hypercube. The
similarity model, although true descriptively, does not seem to
be able to account for the affirmative selection of a specific
mate.
The idiographic model proposes that we each use idiosyn-
cratic criteria, specific enough so that, when we encounter a
potential mate who satisfies those criteria, that individual is
singled out and recognized as right for us. This model predicts
that MZ twins should have very similar criteria and, therefore,
that the spouses of MZ twins should be very similar in some
subset of characteristics, perhaps a different configuration of
characteristics for each MZ twin pair. Because we could not
assess all possible criteria1 attributes, we cannot claim to have
refuted this prediction absolutely. In terms of the 74 varied
attributes that we did assess, however, no evidence supporting
the idiographic model was observed.
Two other tests similarly failed to yield support for the simi-
larity, the idiographic, or any model of lawful mate selection.
Asked to rate their attraction toward their cotwins’ mate at the
time the cotwin became engaged, MZ twins were not more
likely than DZ twins to report that they too were attracted to
their cotwins’ choice; indeed, as many of both types of cotwin
reported negative attitudes as reported positive attitudes toward
their cotwins’ mate selection. We could, of course, invoke ad
hoc psy odynamic reasons to account for these results. It is
possible,7 or example, that twins actively suppress a tendency to
compete for the cotwin’s choice, MZ twins more strongly than
DZ twins, so that the expected pattern of mainly positive attrac-
tion, especially among MZ twins, is changed to correspond to
the pattern we observe, namely, the pattern one would expect if
unrelated pairs of individuals were asked to assess each other’s
mate selections. In the context of the other findings here re-
ported, we think our interpretation is more likely: Although
twins tend to make similar choices in other areas of living,
choices that reflect their genetic and environmental similarity,
their choices of mates are an exception. Although twins, like
singletons, tend to marry persons who are rather similar to
themselves, that is, they tend to select mates from among the
same roughly 50% of the candidate pool, their specific choices
within that pool are no more alike than the choices made by
unrelated random pairs.
Finally, we find that the singleton wives of MZ twins report
no special attraction toward their mates’ twin brothers. Spouses
of DZ twins, of both sexes, more often report negative than
positive attraction toward their spouses’ DZ cotwin. We cannot
account for the reports of the spouses of DZ twins, but they
clearly do not support the proposition that these spouses chose
their mates for characteristics that are determined either geneti-
cally or by the rearing environment; if they had, then we would
have expected their attitudes toward their twins-in-law to have
been biased positively rather than the reverse. In contrast, the