0:00:07.290,0:00:10.117 We like to think of romantic feelings as spontaneous, 0:00:10.117,0:00:13.283 and indescribable things that come from the heart. 0:00:13.283,0:00:15.571 But it's actually your brain running a complex 0:00:15.571,0:00:18.770 series of calculations within a matter of seconds 0:00:18.770,0:00:21.757 that's responsible for determining attraction. 0:00:21.757,0:00:23.883 Doesn't sound quite as poetic, does it? 0:00:23.883,0:00:26.393 But just because the calculations are happening in your brain 0:00:26.393,0:00:30.158 doesn't mean those warm, fuzzy feelings are all in your head. 0:00:30.158,0:00:32.675 In fact, all five of your senses play a role, 0:00:32.675,0:00:36.805 each able to vote for, or veto, a budding attraction. 0:00:36.805,0:00:39.549 The eyes are the first components in attraction. 0:00:39.549,0:00:41.237 Many visual beauty standards vary 0:00:41.237,0:00:43.116 between cultures and eras, 0:00:43.116,0:00:45.665 and signs of youth, fertility and good health, 0:00:45.665,0:00:47.482 such as long lustrous hair, 0:00:47.482,0:00:49.851 or smooth, scar-free skin, 0:00:49.851,0:00:51.312 are almost always in demand 0:00:51.312,0:00:54.384 because they're associated with reproductive fitness. 0:00:54.384,0:00:56.331 And when the eyes spot something they like, 0:00:56.331,0:00:58.598 our instinct is to move closer 0:00:58.598,0:01:00.943 so the other sense can investigate. 0:01:00.943,0:01:02.819 The nose's contribution to romance 0:01:02.819,0:01:05.612 is more than noticing perfume or cologne. 0:01:05.612,0:01:08.237 It's able to pick up on natural chemicals signals 0:01:08.237,0:01:09.803 known as pheromones. 0:01:09.803,0:01:11.659 These not only convey important 0:01:11.659,0:01:14.553 physical or genetic information about their source, 0:01:14.553,0:01:16.764 but are able to activate a physiological 0:01:16.764,0:01:20.054 or behavioral response in the recipient. 0:01:20.054,0:01:24.196 In one study, a group of women at different points in their ovulation cycles 0:01:24.196,0:01:26.525 wore the same t-shirts for three nights. 0:01:26.525,0:01:29.005 After male volunteers were randomly assigned 0:01:29.005,0:01:31.266 to smell either one of the worn shirts, 0:01:31.266,0:01:32.997 or a new unworn one, 0:01:32.997,0:01:36.765 saliva samples showed an increase in testosterone 0:01:36.765,0:01:40.531 in those who had smelled a shirt worn by an ovulating woman. 0:01:40.531,0:01:42.199 Such a testosterone boost 0:01:42.199,0:01:44.768 may give a man the nudge to persue a woman 0:01:44.768,0:01:47.028 he might not have otherwise noticed. 0:01:47.028,0:01:49.183 A woman's nose is particularly attuned 0:01:49.183,0:01:51.303 to MHC molecules, 0:01:51.303,0:01:53.361 which are used to fight disease. 0:01:53.361,0:01:55.617 In this case, opposites attract. 0:01:55.617,0:01:58.148 When a study asked women to smell t-shirts 0:01:58.148,0:02:00.056 that had been worn by different men, 0:02:00.056,0:02:02.193 they preferred the odors of those whose 0:02:02.193,0:02:05.176 MHC molecules differed from theirs. 0:02:05.176,0:02:06.402 This makes sense. 0:02:06.402,0:02:09.109 Genes that result in a greater variety of immunities 0:02:09.109,0:02:12.507 may give offspring a major survival advantage. 0:02:12.507,0:02:15.235 Our ears also determine attraction. 0:02:15.235,0:02:18.660 Men prefer females with high-pitched, breathy voices, 0:02:18.660,0:02:20.828 and wide formant spacing, 0:02:20.828,0:02:22.864 correlated with smaller body size. 0:02:22.864,0:02:25.402 While women prefer low-pitched voices 0:02:25.402,0:02:27.316 with a narrow formant spacing 0:02:27.316,0:02:29.565 that suggest a larger body size. 0:02:29.565,0:02:31.013 And not surprisingly, 0:02:31.013,0:02:33.530 touch turns out to be crucial for romance. 0:02:33.530,0:02:34.921 In this experiment, 0:02:34.921,0:02:37.220 not realizing the study had begun, 0:02:37.220,0:02:40.998 participants were asked to briefly hold the coffee, 0:02:40.998,0:02:42.746 either hot or iced. 0:02:42.746,0:02:44.505 Later, the participants read a story 0:02:44.505,0:02:46.274 about a hypothetical person, 0:02:46.274,0:02:48.406 and were asked to rate their personality. 0:02:48.406,0:02:50.843 Those who had held the hot cup of coffee 0:02:50.843,0:02:53.738 perceived the person in the story as happier, 0:02:53.738,0:02:57.556 more social, more generous and better natured 0:02:57.556,0:03:00.270 than those who had held the cup of ice coffee, 0:03:00.270,0:03:04.793 who rated the person as cold, stoic, and unaffectionate. 0:03:04.793,0:03:06.583 If a potential mate has managed to pass 0:03:06.583,0:03:09.378 all these tests, there's still one more: 0:03:09.378,0:03:11.979 the infamous first kiss, 0:03:11.979,0:03:13.976 a rich and complex exchange 0:03:13.976,0:03:16.508 of tacticle and chemical cues, 0:03:16.508,0:03:18.210 such as the smell of one's breath, 0:03:18.210,0:03:20.234 and the taste of their mouth. 0:03:20.234,0:03:22.076 This magical moment is so critical 0:03:22.076,0:03:24.052 that a majority of men and women 0:03:24.052,0:03:26.377 have reported losing their attraction to someone 0:03:26.377,0:03:28.931 after a bad first kiss. 0:03:28.931,0:03:30.318 Once attraction is confirmed, 0:03:30.318,0:03:31.696 your bloodstream is flooded 0:03:31.696,0:03:33.229 with norepinephrine, 0:03:33.229,0:03:35.541 activating your fight or flight system. 0:03:35.541,0:03:37.163 Your heart beats faster, 0:03:37.163,0:03:38.533 your pupils dialate, 0:03:38.533,0:03:41.647 and your body releases glucose for additional energy, 0:03:41.647,0:03:43.084 not because you're in danger, 0:03:43.084,0:03:44.608 but because your body is telling you 0:03:44.608,0:03:46.308 that something important is happening. 0:03:46.318,0:03:47.828 To help you focus, 0:03:47.828,0:03:50.330 norepinephrine creates a sort of tunnel-vision, 0:03:50.330,0:03:52.625 blocking out surrounding distractions, 0:03:52.625,0:03:55.047 possibly even warping your sense of time, 0:03:55.047,0:03:57.338 and enhancing your memory. 0:03:57.338,0:04:01.139 This might explain why people never forget their first kiss. 0:04:01.139,0:04:03.058 The idea of so much of our attraction 0:04:03.058,0:04:06.323 being influenced by chemicals and evolutionary biology 0:04:06.323,0:04:09.287 may seem cold and scientific rather than romantic, 0:04:09.287,0:04:11.323 but the next time you see someone you like 0:04:11.323,0:04:15.344 try to appreciate how your entire body is playing matchmaker 0:04:15.344,0:04:18.700 to decide if that beautiful stranger is right for you.