男と女では「愛しているよ」というひと言を求めるタイミングが違う。一般的に、男は「行為」の前に言われるのを好むけれど、女は後に言われた方が嬉しい。そしてそれは、進化のうえで自然なことだという。

Let’s get serious: Communicating commitment in romantic relationships.

Are men or women more likely to confess love first in romantic relationships? And how do men and women feel when their partners say “I love you”? An evolutionary economics perspective contends that women and men incur different potential costs and gain different potential benefits from confessing love. Across 6 studies testing current and former romantic relationships, we found that although people think that women are the first to confess love and feel happier when they receive such confessions, it is actually men who confess love first and feel happier when receiving confessions. Consistent with predictions from our model, additional studies have shown that men’s and women’s reactions to love confessions differ in important ways depending on whether the couple has engaged in sexual activity. These studies have demonstrated that saying and hearing “I love you” has different meanings depending on who is doing the confessing and when the confession is being made. Beyond romantic relationships, an evolutionary economics perspective suggests that displays of commitment in other types of relationships and reactions to these displays will be influenced by specific, functional biases. (Journal of Personality and Social Psychology, Feb 14, 2011)

MITの研究者の論文です。

簡単に言えば、男の場合、自らの遺伝子を多く残すためには、できるだけ多くのチャンスを作った方が有利なので、行為の前に愛をばらまくことになる。一方、女の場合、自らの遺伝子を確実に残すためには、妊娠後子どもが生まれるまで大切に育てる必要がある。だから行為の後の愛が重要だというわけ。

「愛しているよ」まで進化心理学で説明するか。なるほどなあ。