WEBVTT - Ep91 "What is love?" 0:00:05.160 --> 0:00:06.200 What is love? 0:00:06.640 --> 0:00:09.440 What does it have to do with how you were raised, 0:00:09.560 --> 0:00:13.040 or the symmetry of someone's face or the smell of 0:00:13.080 --> 0:00:16.200 their underarms. What are we talking about when we talk 0:00:16.239 --> 0:00:20.079 about love and why does it change throughout our lives? 0:00:20.680 --> 0:00:23.520 What do we learn from heartbreak? And what does this 0:00:23.600 --> 0:00:27.040 have to do with sweaty T shirts or rom coms 0:00:27.440 --> 0:00:32.520 or little rodents called prairie voles or the future of love. 0:00:35.200 --> 0:00:37.960 Welcome to Inner Cosmos with me David Eagleman. I'm a 0:00:38.000 --> 0:00:41.680 neuroscientist and an author at Stanford and in these episodes, 0:00:41.800 --> 0:00:46.080 we sail deeply into our three pound universe to understand 0:00:46.120 --> 0:00:49.080 why and how our lives look the way they do. 0:00:49.520 --> 0:00:53.440 And today's episode, in honor of Valentine's Day, is about 0:00:53.760 --> 0:00:59.840 love and neurobiology. What unseen sparks in the skull set 0:00:59.840 --> 0:01:03.639 the heart ablaze whenever that person is nearby. 0:01:09.319 --> 0:01:09.600 Love. 0:01:09.840 --> 0:01:12.440 There aren't many words in our language that carry as 0:01:12.520 --> 0:01:16.479 much weight or as much complexity as that one. As 0:01:16.520 --> 0:01:19.360 we know from the pens of the lyric poets and 0:01:19.360 --> 0:01:23.760 from our own experiences, love can make us feel invincible, 0:01:23.840 --> 0:01:27.480 like we've discovered a secret force that governs the universe. 0:01:27.520 --> 0:01:31.560 It can also make us feel weak and desperate and broken. 0:01:32.080 --> 0:01:36.360 It can make us do things that seem in hindsight irrational. 0:01:36.680 --> 0:01:40.080 Love is one of the main fuels behind the painting 0:01:40.200 --> 0:01:45.679 of masterpieces, the writing of poetry, the composition of symphonies. 0:01:46.120 --> 0:01:49.800 Love has inspired a large fraction of the stories in 0:01:49.840 --> 0:01:53.640 our literature, whether we're talking about Romeo and Juliet or 0:01:53.840 --> 0:01:57.560 Pride and Prejudice, or every rom com that follows the 0:01:57.560 --> 0:02:01.400 same formula, and somehow we never get tired of it. 0:02:01.960 --> 0:02:06.680 And love also drives real, concrete actions. It's the reason 0:02:06.720 --> 0:02:09.240 a mother will throw herself in front of danger to 0:02:09.280 --> 0:02:13.120 protect her child. It's the reason, at least in some cases, 0:02:13.200 --> 0:02:17.560 why when thousand ships can be launched for war. Love 0:02:17.680 --> 0:02:20.960 is a powerful force in the human story. But the 0:02:21.040 --> 0:02:24.919 question that a biologist might ask is what is love? 0:02:25.560 --> 0:02:28.920 Is it an emotion like anger or sadness? Is it 0:02:29.000 --> 0:02:34.080 something deeper? Is it a biological drive like hunger or thirst? 0:02:34.440 --> 0:02:37.320 Is it a trick played on us by evolution to 0:02:37.440 --> 0:02:41.200 keep us reproducing. So that's what we're going to unpack today. 0:02:41.880 --> 0:02:45.760 But here's the starting point. Love is biological. It's a 0:02:45.919 --> 0:02:49.720 symphony of neural circuits firing in just the right patterns 0:02:50.000 --> 0:02:54.640 and a well timed dance of neurotransmitters and hormones. So 0:02:54.680 --> 0:02:57.040 the first question we're going to ask is, as we 0:02:57.200 --> 0:03:01.840 come to tie the experience of love to biology and 0:03:01.960 --> 0:03:06.160 words like limbic system and dopamine and oxytocin, does that 0:03:06.280 --> 0:03:11.120 make love less meaningful or does it make it more profound? So, 0:03:11.240 --> 0:03:13.800 before we get into the meat of today's episode, I 0:03:13.840 --> 0:03:16.800 want to tackle that question head on by reading a 0:03:16.960 --> 0:03:21.720 very short story called Blueprints from my book Some we 0:03:21.760 --> 0:03:25.760 look forward to finding out answers in the afterlife, where 0:03:25.760 --> 0:03:28.919 in luck. In the afterlife, we are granted the ultimate 0:03:28.960 --> 0:03:34.960 gift of revelation, an opportunity to view the underlying code. 0:03:35.040 --> 0:03:38.760 At first, we may be shocked to watch ourselves represented 0:03:39.120 --> 0:03:43.520 as a giant collection of numbers as we go about 0:03:43.560 --> 0:03:47.360 our normal business in the afterlife. In our mind's eye, 0:03:47.400 --> 0:03:51.760 we can see the massive landscape of numbers stretching to 0:03:51.920 --> 0:03:56.360 site's limit. In all directions. This set of numbers represents 0:03:56.400 --> 0:04:00.440 every aspect of our lives. Across its vast plane, we 0:04:00.480 --> 0:04:06.640 spot islands of sevens, jungles of threes, branching rivers of zeros. 0:04:07.240 --> 0:04:11.880 The size and richness are breathtaking as you interact with 0:04:11.960 --> 0:04:15.280 a lover, you can see her numbers as well, and 0:04:15.600 --> 0:04:20.480 her interactions with yours. She endearingly sticks out her bottom 0:04:20.560 --> 0:04:25.760 lip for attention, and your numbers cascade into acrobatics. Digits 0:04:25.880 --> 0:04:30.159 flip their values like waterfalls. As a result, your eyes 0:04:30.279 --> 0:04:34.360 lock onto hers, and amorous words form on your lips 0:04:34.600 --> 0:04:36.560 and travel from your throat. 0:04:36.279 --> 0:04:37.599 In air compression waves. 0:04:38.000 --> 0:04:42.039 As she processes the words, her numbers flip waves of 0:04:42.200 --> 0:04:46.800 change rippling through her system. She returns your affection as 0:04:46.839 --> 0:04:50.200 dictated by the state of her numbers. My goodness, you 0:04:50.279 --> 0:04:54.599 realize on your first afternoon here, this is totally deterministic. 0:04:55.320 --> 0:04:59.599 Is love simply an operation of the math? After watching 0:04:59.720 --> 0:05:04.520 enough code, a new notion of agency and responsibility dawns. 0:05:05.080 --> 0:05:07.400 You watch and understand. 0:05:07.080 --> 0:05:10.240 All the signals that lead to a driver stomping on 0:05:10.320 --> 0:05:13.560 her brakes as her numbers are changed by the numbers 0:05:13.839 --> 0:05:16.360 of the cat walking in front of the wheels. You 0:05:16.400 --> 0:05:19.080 can even see the code of the fleas that leap 0:05:19.160 --> 0:05:22.280 off when the cat leaps. Whether the cat is struck 0:05:22.400 --> 0:05:26.080 or not struck, you now understand, was not in anyone's control. 0:05:26.200 --> 0:05:28.360 It was all in the numbers. 0:05:28.360 --> 0:05:32.720 Married together in a gorgeous inevitability. But we also come 0:05:32.760 --> 0:05:35.400 to understand that the network of numbers is so dense 0:05:35.800 --> 0:05:39.760 that it transcends simple notions of cause and effect. We 0:05:39.880 --> 0:05:43.680 become open to the wisdom of the flow of the patterns. 0:05:44.160 --> 0:05:47.880 If you assume this gift of revelation is received in heaven. 0:05:47.960 --> 0:05:49.000 You're only half right. 0:05:49.360 --> 0:05:53.040 It is also the punishment designed for you in hell. 0:05:53.720 --> 0:05:57.200 The rewards originally thought to offer it as a gift, 0:05:57.200 --> 0:06:01.040 but the punishers quickly decided they could leverage it as 0:06:01.080 --> 0:06:05.520 a kind of affliction, drying up life's pleasures by revealing 0:06:05.800 --> 0:06:11.440 their bloodlessly mechanical nature. Now the rewarders and the punishers 0:06:11.480 --> 0:06:14.559 are in a battle to determine which of them gets 0:06:14.600 --> 0:06:16.320 more benefit out of this tool. 0:06:16.920 --> 0:06:19.200 Will humans appreciate. 0:06:18.520 --> 0:06:21.640 The knowledge or be tortured by it? The next time 0:06:21.640 --> 0:06:25.560 you're pursuing a new lover in the afterlife, perhaps sharing 0:06:25.600 --> 0:06:27.960 a bottle of wine after what appeared to be a 0:06:28.080 --> 0:06:32.479 chance encounter, don't be surprised if both a rewarder and 0:06:32.520 --> 0:06:36.680 a punisher sneak up behind you, the reward whispers into 0:06:36.680 --> 0:06:40.080 one of your ears. Isn't it wonderful to understand the 0:06:40.120 --> 0:06:45.120 code the punisher hisses into your other ear, does understanding 0:06:45.120 --> 0:06:48.920 the mechanics of attraction suck all the life out of it? 0:06:50.080 --> 0:06:53.520 Such a scene is typical in the afterlife and illustrates 0:06:53.560 --> 0:06:58.520 how much both parties have overestimated us. This game always 0:06:58.600 --> 0:07:02.279 ends in disappointment for both sides, who are freshly distraught 0:07:02.560 --> 0:07:06.200 to learn that being let into the secrets behind the 0:07:06.279 --> 0:07:11.320 scenes has little effect on our experience. The secret codes 0:07:11.360 --> 0:07:14.679 of life, whether presented as a gift or a burden, 0:07:15.160 --> 0:07:19.560 go totally unappreciated, and once again the rewarder and the 0:07:19.600 --> 0:07:24.640 punisher skulk off, struggling to understand why knowing the code 0:07:24.960 --> 0:07:29.240 behind the wine does not diminish its pleasure on your tongue. 0:07:29.920 --> 0:07:35.080 Why knowing the inescapability of heartache does not reduce its sting. 0:07:35.760 --> 0:07:40.520 Why glimpsing the mechanics of love does not alter its 0:07:40.560 --> 0:07:46.200 intoxicating appeal. That was the story Blueprints from my book 0:07:46.280 --> 0:07:48.520 sum and that was my way of arguing that it's 0:07:48.680 --> 0:07:53.040 possible for us to deeply study the biological codes that 0:07:53.160 --> 0:07:57.760 underlie love, and no amount of knowledge about the biology 0:07:57.800 --> 0:08:03.360 the codes will ever touch direct experience of love. In fact, 0:08:03.400 --> 0:08:07.560 as science has taught us for centuries, deeper insight generally 0:08:07.640 --> 0:08:12.120 only enhances the splendor. You may know the story about 0:08:12.120 --> 0:08:15.640 the physicist Richard Feinman. He was talking with an artist 0:08:15.760 --> 0:08:18.440 friend of his who held up a flower and said, 0:08:18.880 --> 0:08:22.680 look how beautiful this flower is, and Feineman agreed. And 0:08:22.680 --> 0:08:26.040 then his friend said, I, as an artist, can see 0:08:26.040 --> 0:08:29.080 how beautiful this is, but you, as a scientist, take 0:08:29.160 --> 0:08:32.000 this all apart, and it becomes a dull thing. First 0:08:32.000 --> 0:08:35.400 of all, Feineman pointed out quote, the beauty that he 0:08:35.480 --> 0:08:38.000 sees is available to other people and to me too. 0:08:38.520 --> 0:08:42.120 Although I may not be as refined aesthetically as he is, 0:08:42.240 --> 0:08:45.360 I can appreciate the beauty of a flower. At the 0:08:45.400 --> 0:08:48.640 same time, I see much more about the flower than 0:08:48.679 --> 0:08:52.000 he sees. I can imagine the cells in there, the 0:08:52.040 --> 0:08:56.240 complicated actions inside, which also have a beauty. I mean, 0:08:56.280 --> 0:08:59.079 it's not just beauty at this dimension at one centimeters, 0:08:59.080 --> 0:09:03.040 there's also beauty and smaller dimensions, the inner structure, also 0:09:03.400 --> 0:09:04.280 the processes. 0:09:04.600 --> 0:09:05.640 The fact that the. 0:09:05.480 --> 0:09:09.600 Colors in the flower evolved in order to attract insects 0:09:09.600 --> 0:09:12.760 to pollinate it is interesting. It means that insects can 0:09:12.800 --> 0:09:16.160 see the color. It adds a question. Does this esthetic 0:09:16.320 --> 0:09:20.160 sense also exist in the lower forms. Why is it esthetic? 0:09:20.520 --> 0:09:24.200 All kinds of interesting questions which the science knowledge only 0:09:24.360 --> 0:09:28.200 adds to the excitement, the mystery, and the awe of 0:09:28.240 --> 0:09:32.320 a flower. It only adds end quote. So with this 0:09:32.440 --> 0:09:36.040 in mind, that knowledge only adds to the awe and 0:09:36.120 --> 0:09:38.520 beauty we can appreciate, we're going to dive into the 0:09:38.559 --> 0:09:42.120 science of love. What happens in the brain when we 0:09:42.200 --> 0:09:45.319 fall in love? Why does attraction feel so intense? What 0:09:45.360 --> 0:09:48.839 does heartbreak have in common with physical pain? And what 0:09:49.000 --> 0:09:53.640 makes long term love last? So let's begin inside the brain. 0:09:54.040 --> 0:09:56.880 When we look at the circuitry and chemicals in the brain, 0:09:56.960 --> 0:10:01.720 we find that love correlates with particular patterns, they carefully 0:10:02.040 --> 0:10:05.679 balanced mixture of different areas and molecules. So how can 0:10:05.720 --> 0:10:08.560 this be studied? Well, I'll give you an example. In 0:10:08.559 --> 0:10:11.680 two thousand and five, Helen Fisher and her colleagues published 0:10:11.720 --> 0:10:14.360 a new kind of study. They were thinking about how 0:10:14.440 --> 0:10:18.840 scientists have long described the things that animals do to 0:10:18.920 --> 0:10:22.000 attract mates, but there was almost nothing known about the 0:10:22.040 --> 0:10:26.720 brain mechanisms by which the mate becomes attracted. So they 0:10:26.760 --> 0:10:30.240 set up a study with brain imaging fMRI, and they 0:10:30.240 --> 0:10:32.640 scanned a bunch of college kids who were in the 0:10:32.880 --> 0:10:37.600 throes of romantic love. The participants viewed pictures of that 0:10:37.920 --> 0:10:41.079 special someone, and they also looked at pictures of acquaintances, 0:10:41.320 --> 0:10:44.160 and the photos of the people they were romantically involved 0:10:44.200 --> 0:10:48.680 with caused the participant's brain to become active in regions 0:10:48.720 --> 0:10:52.760 that traffic in dopamine, like the caudate nucleus, which is 0:10:53.000 --> 0:10:58.000 associated with reward detection and expectation, and the ventral tegmental area, 0:10:58.240 --> 0:11:00.920 which spits out dopamine all over the brain and is 0:11:00.960 --> 0:11:05.120 associated with pleasure and focused attention and the motivation to 0:11:05.200 --> 0:11:08.720 pursue and acquire rewards, and is by the way, a 0:11:08.960 --> 0:11:13.240 very evolutionarily old circuit. So this is what's thought to 0:11:13.320 --> 0:11:18.719 make love euphoric, like cocaine or alcohol. You've certainly heard 0:11:18.760 --> 0:11:22.240 of dopamine as a molecule that drives addiction and craving, 0:11:22.280 --> 0:11:26.360 whether we're talking about sugar or gambling or social media. 0:11:26.480 --> 0:11:29.000 I don't want to oversimplify the story of dopamine, but 0:11:29.080 --> 0:11:34.440 presumably this is why new love feels so exhilarating, and 0:11:34.480 --> 0:11:37.840 why time spent with that person feels so rewarding, and 0:11:37.880 --> 0:11:41.800 why being away from them feels like withdrawal. Now These 0:11:41.800 --> 0:11:45.600 dopamine systems link with other brain areas, for example, the 0:11:45.679 --> 0:11:49.240 nucleus ccumbins, the amignala, the hippocampus pre federal cortex, and 0:11:49.320 --> 0:11:55.040 these areas all collaborate to keep chasing pleasurable behavior. And 0:11:55.080 --> 0:11:58.319 this is the same circuitry we see getting juiced up 0:11:58.640 --> 0:12:02.160 in sex and food and drugs. So when we're falling 0:12:02.200 --> 0:12:07.160 in love, chemicals associated with the reward circuits flood our 0:12:07.200 --> 0:12:09.640 brains and this gives us a number of things that 0:12:09.679 --> 0:12:13.480 we recognize in love. The faster heart, the sweatier palms, 0:12:13.520 --> 0:12:17.880 the flush cheeks, the feelings of passion and anxiety. When 0:12:17.920 --> 0:12:21.480 people talk about love being like a drug, this is 0:12:21.559 --> 0:12:24.960 what they have in common. But dopamine is only part 0:12:24.960 --> 0:12:29.240 of this equation. During this initial phase of romantic love, 0:12:29.280 --> 0:12:32.959 you also get more of the stress hormone cortisol, which 0:12:33.080 --> 0:12:35.880 essentially tells your body there's a crisis you have to 0:12:35.960 --> 0:12:39.240 deal with. And this is presumably why the person of 0:12:39.280 --> 0:12:43.040 your attraction can take up so much mental real estate. 0:12:43.480 --> 0:12:47.000 This is the object to be attended. And there's more. 0:12:47.480 --> 0:12:52.480 During that first swell of passion, there's a neuromodulator slash 0:12:52.520 --> 0:12:56.720 hormone called oxytocin that starts playing a big role. This 0:12:56.800 --> 0:13:00.560 gets released when we hug, while we cuddle, when we 0:13:00.600 --> 0:13:05.439 make eye contact. Oxytocin is released during sex and it's 0:13:05.480 --> 0:13:09.560 heightened by skinned skin contact, and it deepens these feelings 0:13:09.600 --> 0:13:13.240 of attachment and it makes couples feel closer to one 0:13:13.280 --> 0:13:16.840 another after having sex. And there are lots of other players, 0:13:16.920 --> 0:13:20.440 like testosterone in men and women that seems to be 0:13:20.520 --> 0:13:24.560 heightened during this initial attraction. It's possibly associated with what 0:13:24.640 --> 0:13:29.360 makes desire feel urgent and what intensifies the physical attraction 0:13:29.679 --> 0:13:33.920 in early relationships. High testosterone levels correlate with this intense 0:13:33.960 --> 0:13:37.199 attraction and with risk taking behavior. Now we put all 0:13:37.200 --> 0:13:39.200 this together, and it gives us a little bit of 0:13:39.240 --> 0:13:43.160 insight into the old expression that love is blind. And 0:13:43.200 --> 0:13:47.200 that's because romance seems to also tamp down the neural 0:13:47.280 --> 0:13:51.800 pathways involved in fear and social judgment. In other words, 0:13:52.080 --> 0:13:55.880 when your heart's on fire, smoke gets into the neural 0:13:55.920 --> 0:13:59.800 machinery that's normally making critical assessments of the other. 0:14:01.000 --> 0:14:02.160 That's why early. 0:14:01.920 --> 0:14:05.600 Stage love makes us overlooked flaws, why it makes us 0:14:05.960 --> 0:14:26.640 idealize our partners, why we sometimes ignore red flags. Okay, 0:14:26.680 --> 0:14:29.360 so there are ways to study romantic love in the 0:14:29.440 --> 0:14:32.480 brain in terms of the circuitry and chemicals, but you 0:14:32.520 --> 0:14:36.120 can study the behavioral aspects as well. Who do we 0:14:36.200 --> 0:14:39.480 find ourselves attracted to and why? And what I've always 0:14:39.480 --> 0:14:42.120 found so wild is the way that our sense of 0:14:42.200 --> 0:14:46.520 attraction runs entirely under the hood. There's essentially no conscious 0:14:46.520 --> 0:14:49.560 awareness of any of it. You just find yourself attracted 0:14:49.600 --> 0:14:53.400 to some people more than others. The first blushes of 0:14:53.480 --> 0:14:57.080 love feel like magic, But underneath the poetry, underneath the 0:14:57.680 --> 0:15:04.200 longing glances and racing heartbeat, attraction is a neural algorithm. Now, 0:15:04.440 --> 0:15:07.840 we generally like to believe that we consciously choose our partners, 0:15:07.880 --> 0:15:10.640 but a closer study tells us that our brains are 0:15:10.680 --> 0:15:14.240 making calculations we're not even aware of pulling the strings 0:15:14.240 --> 0:15:18.239 behind the scenes. So let's start with something visual. Facial symmetry. 0:15:18.640 --> 0:15:21.560 A number of studies show that people across different cultures 0:15:21.600 --> 0:15:24.600 are more attracted to symmetrical faces. 0:15:25.000 --> 0:15:25.360 Why. 0:15:25.760 --> 0:15:29.080 One hypothesis is that symmetry is a marker of good 0:15:29.120 --> 0:15:34.360 genetic health. Through evolution, humans developed an unconscious preference for 0:15:34.440 --> 0:15:40.000 partners who show fewer signs of developmental instability. A more 0:15:40.000 --> 0:15:45.560 symmetrical face presumably means fewer genetic mutations, better resistance disease, 0:15:46.000 --> 0:15:49.600 and higher likelihood to produce healthy offspring. And it's not 0:15:49.680 --> 0:15:53.479 just symmetry. Certain features about other people are universally attractive, 0:15:53.560 --> 0:15:57.200 even across different cultures. Men are drawn to features that 0:15:57.360 --> 0:16:02.640 signal fertility. Curvy bar body, high cheek, bones, full lips, 0:16:02.680 --> 0:16:05.800 all things that young girls and older women don't have. 0:16:06.080 --> 0:16:08.400 Women tend to be attracted to different features, but the 0:16:08.400 --> 0:16:11.640 same idea. It's signals of fertility. In the male, things 0:16:11.680 --> 0:16:17.320 like strong jawlines or prominent browridges. More rugged features are 0:16:17.360 --> 0:16:21.520 associated with higher testosterone, and its signs that young boys 0:16:21.520 --> 0:16:25.760 and old men don't generally have. It indicates fertility. But 0:16:25.800 --> 0:16:30.560 attraction isn't only about appearance. It's also about familiarity. People 0:16:30.680 --> 0:16:33.040 often end up dating someone who looks just a bit 0:16:33.240 --> 0:16:35.840 like them. There's a reason for that. We are wired 0:16:35.880 --> 0:16:39.480 to find comfort in the familiar. In some cases, this 0:16:39.600 --> 0:16:43.920 means we unconsciously seek out people who resemble our parents 0:16:44.000 --> 0:16:48.240 because their faces are imprinted in our early neural development 0:16:48.320 --> 0:16:53.840 as safe and trustworthy. This is called positive assortative mating, 0:16:54.120 --> 0:16:56.920 which just captures the idea that we are often attracted 0:16:57.000 --> 0:17:01.040 people who share our own physical or genetic traits. If 0:17:01.040 --> 0:17:04.359 you examine married couples, you'll find that they're more likely 0:17:04.440 --> 0:17:09.000 than chance to have similar eye colors, hair textures, levels 0:17:09.080 --> 0:17:12.399 of attractiveness. There are many reasons for this, things like 0:17:12.440 --> 0:17:16.320 implicit egotism, and there's individual differences in how much people 0:17:16.400 --> 0:17:19.080 want a mate to look like them, But on average 0:17:19.160 --> 0:17:22.439 this is true. So while we think we're making independent 0:17:22.520 --> 0:17:26.280 choices in love, our brains are actually navigating us in 0:17:26.560 --> 0:17:30.439 patterns even when we don't recognize them. But attraction is 0:17:30.440 --> 0:17:33.200 about far more than what we see. It also involves 0:17:33.400 --> 0:17:37.440 what we smell. As I talked about in episode eighty nine, humans, 0:17:37.600 --> 0:17:41.760 like all our animal cousins, communicate through pheromones, which are 0:17:42.119 --> 0:17:47.240 chemical signals that influence social and sexual behaviors. So while 0:17:47.240 --> 0:17:50.560 we have no conscious awareness of them, they play a 0:17:50.640 --> 0:17:54.200 role in determining who we find attractive. So one experiment 0:17:54.280 --> 0:17:57.679 on this was the Sweaty T Shirt Study, which was 0:17:57.680 --> 0:18:01.119 conducted by Klaus Wedekind and his colleague. Women were asked 0:18:01.160 --> 0:18:04.520 to smell t shirts worn by different men and rate 0:18:04.640 --> 0:18:08.560 which ones smelled the most attractive. The result was that 0:18:08.600 --> 0:18:12.680 the women preferred the scent of men whose immune system 0:18:12.760 --> 0:18:17.400 genes what are called their MHC genes, were somewhat different 0:18:17.440 --> 0:18:19.880 from their own. In other words, the ladies were attracted 0:18:19.920 --> 0:18:23.160 to the guys who were not genetically similar to them. 0:18:23.760 --> 0:18:27.679 Why does this matter well, Evolutionarily, choosing a partner with 0:18:27.720 --> 0:18:32.560 a different immune system means a greater variety of immune 0:18:32.600 --> 0:18:37.240 defenses for potential offspring. It's nature's way of preventing inbreeding 0:18:37.760 --> 0:18:43.719 and ensuring genetic diversity. Now, interestingly, birth control pills disrupt 0:18:43.880 --> 0:18:47.359 this natural process. There were experiments by Craig Roberts and 0:18:47.359 --> 0:18:50.879 colleagues that found that women who are on the pill 0:18:51.240 --> 0:18:55.040 are more likely to choose partners whose immune profiles are 0:18:55.160 --> 0:18:58.480 similar to their own, and that can be problematic because 0:18:58.480 --> 0:19:01.040 when they go off the pill, their attraction to their 0:19:01.080 --> 0:19:04.520 partner can sometimes change. So all this raises a question 0:19:04.600 --> 0:19:08.080 to what extent is the attraction we feel out of 0:19:08.119 --> 0:19:11.000 our hands. If something as small as a birth control 0:19:11.040 --> 0:19:16.280 pill can alter our romantic preferences, what else is shaping 0:19:16.320 --> 0:19:20.080 our choices without us realizing it. While psychologists have long 0:19:20.160 --> 0:19:25.080 noticed that attraction isn't just shaped by these immediate biological factors, 0:19:25.080 --> 0:19:29.359 it's also shaped by our past. So Researchers talk about 0:19:29.400 --> 0:19:33.960 three primary attachment styles that are formed in early childhood 0:19:34.160 --> 0:19:38.640 and this influences how we approach relationships. So first there's 0:19:38.680 --> 0:19:43.080 people with secure attachment, where they feel comfortable with intimacy. 0:19:43.280 --> 0:19:47.080 They tend to have stable, healthy relationships. But there's also 0:19:47.640 --> 0:19:52.520 anxious attachment and people here crave closeness but have a 0:19:52.560 --> 0:19:56.880 major fear of abandonment. They typically need a lot more 0:19:56.920 --> 0:20:02.120 reassurance in relationships. And then there's avoidant attachment, and here 0:20:02.200 --> 0:20:06.280 people value independence to the point of pushing others away. 0:20:06.720 --> 0:20:10.280 They struggle with commitment. So when you see these different types, 0:20:10.359 --> 0:20:14.000 you start to see patterns when they combine in couples. 0:20:14.000 --> 0:20:18.040 For example, one of the most common and toxic relationship 0:20:18.080 --> 0:20:22.880 patterns is called the anxious avoidant trap. This happens when 0:20:22.920 --> 0:20:27.240 someone with an anxious attachment who craves closeness falls for 0:20:27.320 --> 0:20:31.439 someone with an avoidant attachment who fears closeness, and the 0:20:31.480 --> 0:20:35.200 result is this constant push and pull dynamic, or one 0:20:35.240 --> 0:20:38.879 person chases while the other withdraws. Now, researchers have studied 0:20:38.880 --> 0:20:41.440 this kind of thing in brain scanning, and what they 0:20:41.480 --> 0:20:46.000 find is that people with secure attachment have more regulated 0:20:46.040 --> 0:20:49.680 activity in their pre federal cortex, which presumably allows them 0:20:49.680 --> 0:20:53.719 to process emotions in a balanced way. But people with 0:20:53.840 --> 0:20:57.800 anxious attachment show a lot more activity in regions associated 0:20:57.840 --> 0:21:02.200 with fear and threat detection, so their brains are strongly 0:21:02.320 --> 0:21:06.520 wired up to detect potential rejection. And it's the same 0:21:06.560 --> 0:21:10.879 with people with avoidant attachment styles. They also have cranked 0:21:10.920 --> 0:21:13.199 up threat detection, but in this case it has to 0:21:13.240 --> 0:21:17.560 do with being exposed to cues that trigger feelings of closeness, 0:21:17.800 --> 0:21:20.400 and they also tend to have less activity in reward 0:21:20.560 --> 0:21:26.280 centers for positive social stimuli. So sometimes the paths we 0:21:26.359 --> 0:21:30.680 take aren't about choices in the moment, but patterns set 0:21:30.760 --> 0:21:33.639 down in our brains long before we even enter the 0:21:33.760 --> 0:21:38.159 dating world. And attraction isn't just about biological signals and 0:21:38.280 --> 0:21:39.760 personality compatibility. 0:21:39.760 --> 0:21:41.520 It's also about novelty. 0:21:42.080 --> 0:21:44.920 Remember that the reward systems in the brain are heavily 0:21:45.080 --> 0:21:49.119 geared for novelty, for new experiences. This is why early 0:21:49.200 --> 0:21:54.720 stage romance feel so intense. It's new and unpredictable and exciting. 0:21:54.960 --> 0:21:57.480 The brain gets a lot of dopamine hits when we're 0:21:57.760 --> 0:22:02.240 around someone that we're falling, and it reinforces the sense 0:22:02.280 --> 0:22:05.880 of obsession and pleasure, and just consider this in your 0:22:05.880 --> 0:22:09.920 own life. Sometimes, when you start seeing someone new, everything 0:22:09.960 --> 0:22:13.600 about them is fascinating, the way they laugh, the stories 0:22:13.640 --> 0:22:16.520 they tell, even the way they twitch their nose when 0:22:16.520 --> 0:22:21.200 they laugh. Every moment with them feels electric. But over time, 0:22:21.960 --> 0:22:26.840 this novelty fades. Your brain adapts. What was once thrilling 0:22:26.960 --> 0:22:31.440 becomes familiar, and this is where attraction starts to shift. 0:22:31.800 --> 0:22:35.480 Some people chase that initial high, moving from one relationship 0:22:35.520 --> 0:22:38.639 to the next in search of that early stage rush. 0:22:38.840 --> 0:22:43.440 Others transition into long term love. But this raises a 0:22:43.520 --> 0:22:47.760 question can love last forever? We often think about love 0:22:47.880 --> 0:22:51.600 is something that fades over time. The passion cools, the 0:22:51.680 --> 0:22:55.640 excitement diminishes, and eventually that person who once made your 0:22:55.640 --> 0:22:58.760 heart race becomes just another part of your daily routine. 0:22:59.200 --> 0:23:03.400 But is that inevitable? Does love have a neural expiration date? 0:23:04.080 --> 0:23:08.680 Some people argue that monogamy is not natural. After all, 0:23:08.720 --> 0:23:11.440 as we just said, your reward systems thrive on novelty, 0:23:11.880 --> 0:23:17.040 and there are arguments that humans evolved for serial pair bonding, 0:23:17.160 --> 0:23:19.639 meaning we're wired to stay with a partner for a 0:23:19.640 --> 0:23:22.680 certain number of years, often just long enough to raise 0:23:22.760 --> 0:23:26.879 young children before moving on, and there's some evidence for this. 0:23:27.000 --> 0:23:30.840 In many cultures, divorce rates spike around the four year mark, 0:23:31.160 --> 0:23:34.800 so that leads some researchers to suggest that romantic love 0:23:35.280 --> 0:23:38.000 does have a built in expiration date. The brain is 0:23:38.280 --> 0:23:43.119 wired for change, and that long term monogamy requires conscious 0:23:43.200 --> 0:23:47.040 effort rather than biological instinct. And indeed, it's inevitable that 0:23:47.080 --> 0:23:50.320 there's a change in neural activity over time because the 0:23:50.440 --> 0:23:54.800 high energy drug addiction of early romance can't keep going forever. 0:23:55.359 --> 0:23:59.080 But that doesn't mean the spark of passion has to 0:23:59.119 --> 0:24:03.119 get extinguished. There was a study in twenty eleven and 0:24:03.200 --> 0:24:06.520 they performed brain imaging on couples that had been married 0:24:06.800 --> 0:24:10.200 an average of over two decades. So they showed them 0:24:10.240 --> 0:24:13.639 their partner's face, and they also showed control images of 0:24:13.720 --> 0:24:16.600 other faces, like a friend or someone they didn't know well. 0:24:17.160 --> 0:24:20.040 And what they found in response to the loved one 0:24:20.680 --> 0:24:24.640 was the same kind of reward related activity as new 0:24:24.680 --> 0:24:28.040 lovers had, for example in the ventral tegmental area and 0:24:28.119 --> 0:24:32.760 dorsal stratum. In other words, the reward systems involved in 0:24:32.920 --> 0:24:38.119 romantic love can stay sparking along for decades. And what 0:24:38.200 --> 0:24:40.840 they found in the study was that Several other areas 0:24:40.880 --> 0:24:44.000 were active, depending on the kind of relationship the people 0:24:44.040 --> 0:24:47.920 had developed. Some people had a more friendship based love, 0:24:48.280 --> 0:24:51.000 and these folks they saw more activity in the same 0:24:51.080 --> 0:24:54.080 kinds of regions we see in maternal. 0:24:53.680 --> 0:24:55.920 Attachment, like the globis palladus. 0:24:56.200 --> 0:25:00.520 Other brain areas correlated with the couple's frequency of having sex, 0:25:00.960 --> 0:25:04.880 like the hypothalamus and posterior hippocampus. The activity of other 0:25:05.000 --> 0:25:10.040 areas correlated with obsession, like the caud eight. Other areas 0:25:10.080 --> 0:25:14.359 correlated with the degree of romantic love and the inclusion 0:25:14.440 --> 0:25:17.119 of the other in the self areas like the ventral 0:25:17.160 --> 0:25:20.479 tegmental area. Anyway, don't worry about the details, but the 0:25:20.600 --> 0:25:25.000 encouraging thing this demonstrates is that the excitement, the reward 0:25:25.200 --> 0:25:28.960 of romance can stick around. Maybe it mellows a bit, 0:25:29.000 --> 0:25:31.720 but the key is that it's accompanied by more rational 0:25:31.760 --> 0:25:36.119 cognition rather than the emotional roller coaster. In other words, 0:25:36.320 --> 0:25:40.600 reward centers are still cranking along as loving relationships proceed, 0:25:40.960 --> 0:25:46.480 but the relentless itch of desire subsides. Your cortisol and 0:25:46.560 --> 0:25:51.040 other stress hormones gradually return to equilibrium. You get the 0:25:51.200 --> 0:25:55.840 closeness without the overwhelm As a result of these brain changes, 0:25:55.920 --> 0:25:59.800 the connection with your partner deepens into something less obsessive 0:25:59.840 --> 0:26:04.160 in consuming, into something where your partner becomes deeply ingrained 0:26:04.200 --> 0:26:07.880 into your internal model. They work their way into your 0:26:07.880 --> 0:26:12.639 neural circuitry. They literally become a part of you. In 0:26:12.680 --> 0:26:16.480 this way, there's a drift from passionate love into what's 0:26:16.520 --> 0:26:22.960 called compassionate love. Euphoria is slowly replaced with depth. And 0:26:23.040 --> 0:26:27.280 let's return to the neuromodulators. Oxytocin isn't just involved in 0:26:27.320 --> 0:26:31.240 the early throes of romantic love. It also helps transform 0:26:31.600 --> 0:26:38.480