Many mechanisms can produce within-pair similarity of physical attractiveness:
1) Homotypic Preferente
2) Courtship Rejections
3) Strategic Courtship
4) Tentative Relationships
5) Social Stratification.
6. Phenotypic Correlation
What does strategic courtship mean? All people prefer highly attractive individuals yet they know that the attractive candidates are choosy and therefore, in reality, court in a homotypic (assortative) way. Individuals are expected to learn strategic courtship via modulation of their own choosiness in response to mating behavior experienced from others (proposals, acceptances, rejections) and during the course of time [1,2].
There are computer simulations corroborating the importance of this learning process and suggest that modulation of own choosiness by behavior received from others is more effective than its simple decrease with time [3, 4, 5, 6].
In the Ellis and Kelley experiment (people bearing numbers on their foreheads), participants could reliably estimate their own number after the game ended (r ≈ 0.65), and many of the lowly numbered people admitted that they recognized their low attractiveness during the course of game and down-regulated their choosiness and strategy of solicitation 
This means that own attractiveness can be efficiently learnt from social stimuli and impact on mating behaviors. Indeed, lowly attractive people consider interest from and a date with a highly attractive person as being less probable than do attractive people [8, 9].
Therefore strategic mating behaviors were observed in experimental studies, where participants declared the will to date with strangers [10, 11] or newly acquainted persons , or when participants’ involvement in a relationship with a newly acquainted person was analyzed . However, all people in these studies preferred the attractive over unattractive candidates, even though the effect was less marked in lowly- than highly-attractive individuals (or, more specifically, the unattractive people were relatively more tolerant to unattractive candidates). Therefore, the preferences and behaviors were strategic but not homotypic.
However, strategic behaviors are not found in participants of:
a) Blind dates [12, 13, 14, 15, 16], and
b) Online dating [17, 18]. Courtship thus may not be strategic when the number of prospective partners is large and costs of searching or being rejected are low .
The strategic behaviour in courtship can not befall on the online dating environment because costs of sending an e-mail or a cost from rejection are not significant, and a male user may contact a desirable female user although he expects that the probability of a match with this online dater is small. This includes the female user’s expectation of not being contacted by those potential male users that exceed their mate aspiration threshold. Online users, mainly female users, are not cognitively assuming rational expectations (when the subjective and actual probabilities of being accepted coincide); we can infer this expectation from the empirical probability of receiving a reply from the mate, which can be estimated from our data.
Men are more involved in short-term relationships, and therefore are more interested in the number of sexual partners, not so much in the quality of a relationship (Buss, 2006). As a consequence, they are less selective concerning the traits of a partner. However, for long-term relationships, willing to establish a family and to invest in offspring, their behavior changes, and their level of “choosiness” increases. Decreasing the aspiration level of male users is an option to increase their chance to find at least a short-term female partner on the website. However, this also means to allow constructing non-assortative matches, and thus building short-term couples whose attributes do not resemble the attributes of observed couples off-line, a property a mate-matching procedure should guarantee. That is, decreasing the aspiration level of male users impairs the proposed mate-matching strategy rather than to improve it.
The physical attractiveness measure is used as a proxy for the overall attractiveness of a profile. We run the regression (10) separately for users in different groups of physical attractiveness, i.e., we segment the suitors, indexed by i, according to their physical attractiveness, and allow for the possibility that users in different groups respond differently to the attractiveness of the mates that they browse. Figure 1 shows the relationship between a browsed user’s photo rating and the estimated probability that the browser will send a first-contact e-mail. We see that, regardless of the physical attractiveness of the browser, the probability of sending a first-contact e-mail in response to a profile is monotonically increasing in the attractiveness of the photo in that profile. Thus, even if users take the cost of rejection and composing an e-mail into account, this perceived cost is not large enough such that the net expected benefit of hearing back from a very attractive mate would be less than the net expected benefit of hearing back from a less attractive mate. These results suggest that there are no significant costs of e-mailing attractive users, and, consequently, that strategic behavior is of little importance in online dating.
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