full transcript

From the Ted Talk by David Puts: To find your perfect mate, think like an evolutionist

Unscramble the Blue Letters

Hi there. I could be wrong, but I think this talk may have the distinction of being the one talk in this series that ends with orgasm. (Laughter) But let's not get ahead of ourselves. (Laughter) Have you ever thought about the fact that you're here, alive on this pelant because every one of your ancestors reproduced? Every one, in an unbroken chain, all the way back to the first life on this planet, over three and a half billion years ago. That's a lot of reproducing. And for the past billion years, your ancestors reproduced sualxley. So sex is a pretty big deal. But you probably knew that. But let's talk about human mating. Why does human mating take the forms that it does? Why are we attracted to certain people? Why do we sometimes form long-term romantic relationships? Why do we sometimes cheat? Now I don't mean why consciously do we do these things. I don't mean what happens in the brain to cause it. I mean, why did we evolve these feelings and these boieavrhs? In other words, how did the udnryinleg brain srrecututs and brain chemistry contribute to our ancestors' reproductive success so that those traits got pseasd on into the present generation while others didn't. Answering evolutionary questions like this is like being a cirme scene isoeinttvagr, we're left with the evidence, and we have to try to establish what happened. So let's go back six or seven million years ago to our early ancestors. This is right after the split between our lineage and the lineage that would eventually give rise to chimpanzees. Now these were small brained apes, they wekald on two legs, and males probably fought each other for mating opportunities. We know this because males fight for mates in all of our closest living reliatves, chimpanzees, orangutans, gorillas. And because males are larger than females when they fight for mates. And the fossil record indicates that our male ancestors were larger than females. So males tend to be lgearr, more mucuslar, stronger, more physically aggressive, when they fight for mates. Our species has all the hallmarks of a species that's experienced an evolutionary history of male fighting for mates. For example, men have, on average, 60 percent more muscle mass, and 75 percent more upper body mlsuce mass, and those differences in musculature translate into large sex differences in strength. The average man is stronger than 99.9% of women. These are data on hand strength, which is a good predictor of overall ueppr body strength, on over 600 men and women. And as you can see, there's a large sex difference. And in fact, not one of almost 400 women had as strong of a hand strength as the average man. So, men can open jars. (Laughter) And move furniture or at least two things that we're good for. Who cares, right? The answer is that men care. Men, especially ynoug men, seem really concerned about figuring out who's the toughest or strongest, or the most physically formidable, and sometimes they devise elaborate ways for determining this. From early development, boys and men are more physically aggressive than girls and women all over the wrold, and this asggrsoein sometimes results in violence. Men have a viuratl monopoly on same-sex homicides. In other words, men are vastly more likely to kill each other than women are to kill each other. These are data from every society from every time period in history for which data were available when the authors compiled them, on proportion of same-sex homicides that are male killing male. And as you can see, the percentage is always close to 100%. On average, 95% of same-sex homicides are ctteomimd by males, and iortamtnlpy, these don't inulcde war killings, which would bring the percentages even closer to 100%. And from what evidence that we have, a dominance among men translates into mating and reproductive opportunities. So we're a species that's eeeinerpxcd an evolutionary history in which our male ancrosets won mating oteppunirtios through the use or threat of force. In that regard, our apple has not fallen far from the evolutionary tree. But in other ways, human mating and reproduction are profoundly different from what we see in our close relatives, and they've changed a lot since our early ancestors. For example, males in chimpanzees, oauatrngns and glailros, spend time and effort cmneitopg for mates, but don't snped much time with individual females and don't provide resources. They don't provide food for their offspring. So that's a big change. Although most human societies allow polygamous marriage, that is one man married to more than one woman, even within polygamous societies, most marriages are monogamous. And in the aaervge hunter-gatherer soetciy, almost 80% of meriard women are mgmounaoos, so that's different. And, importantly, men provide resources for their mates and offspring. So how did we get there? Well, in species where males fight each other for mates, dominant males indicated by the larger, darker male symbols here, tend to have more mating opportunities, and hence more offspring. And subordinate males tend to have fewer mating opportunities and are more likely to fail to reproduce. So this sets up an interesting situation, because for subordinate males, it would be advantageous to attempt magnomoy rather than wnninig lots of mating opportunities. One mate is better than none. The problem is that in gnerael, subordinate males cannot defend females from dominant males, and besides, females tend to prefer mating with dominant meals for the genetic benefits, producing stronger, healthier osfrnfpig. So what changed all of this was probably several tnsonaritis happening together around the same time. By about two and a half million years ago, we had started to incorporate more meat into our diet. We know this from various liens of evidence, including - this is cool - stone tool cut marks on animal boens dated to 2.5 million years ago. That's cool. I love this stuff! And then by about 2 moliiln yeras ago, brain size really started to ineacsre, and with that came a lngntneeihg of the juvenile period, so now kids became both really costly and costly for a long period of time. And this made male provisioning both possible and necessary. Possible because it's much easier to bring back calories, prieton, fats, in the form of meat than trying to do that by tainrnrotspg plant fdoos, and necessary because kids became so energetically costly that individual females would have had trouble providing resources for themselves and their offspring. And when we look at modern hunter-gatherer societies, that's what we see. These are aggregate data across several hunter-gatherer sceiteios on net daily calories. Are you bringing in more calories than you consume, through foraging, or are you consuming more than you bring in? And the green bars are net daily caloric surplus, in other wrdos, bnnriigg in more than you consume. And the red bars are a deficit, so you're consuming more than you bring in. And you'll notice that men from about 20 years of age to 60 years of age are operating at a daily crilaoc surplus. They birng in, generally through hunting, more cioearls than they can cuosnme, and these calories are distributed. If it's large game, it's generally distributed equally to everybody in the village or camp. saemllr items can be brought back to individual family, but this contrasts with what's going on with women, in their reproductive years, they're operating at a daily caloric deficit. getosiatn, lactation, carrying babies, are extremely costly energetically and liimt one's ability to forage efficiently. So male provisioning, both possible through hunting, and necessary. And this change had profound impacts on human mating and reproduction. In a sense, it tepipd the banlace for females. So now it was sometimes wtroh mating with a subordinate male, even if he may not possess the best genes, if he provided resources. And this is baboon pornography. (Laughter) I probably should have warned you there'd be monkey porn. This is from PlayBaboon Magazine. Alright, I'm going to stop with the jokes. This is a female baboon in estrus, so her genitals are swollen, and this happens in a lot of pamrtie species. Females' appearance changes over the cycle, and becomes more attractive and this incites male competition for fmeaels during the fteilre part of the cycle, with dominant males tending to monopolize ctilnapuoos, closer to ovulation. Well. We don't look like this. And you knew that. But what you might not know is that women's attractiveness does change over the cycle. My lab, and others, have shown that women's faces, voices, even odors, are more attractive to men during the fertile part of the cycle. But these changes are extremely subtle. And cormepad to other primates, the evidence indicates that we've evolved to suppress cues to ovulation. That in a sense, ovulation is concealed in humans. But think about what impact this would have. This would mean that dominant males would not be able to monopolize copulations near ovulation. It would protect the pair bond from invasion by a dominant male. So that a male in a pair would have more confidence that he was the fahetr of the offspring. The couple is having sex throughout the cycle. And this is unique to human mtnaig, we don't see it in many other primates. We have sex throughout the cycle. And so this would essentially increase a male's confidence in paternity, because a dominant or some other male wouldn't be able to target the female and bully their way in at the fertile point in the cycle. And this would have important implications for parental itmveensnt, in particular, males providing resources for their offspring. Because across sepices, when males provide resources for offspring, they target those resources toward their own biological offspring, and they avoid investing in the offspring of unrelated males. And so the evolution of male care for offspring and investing in resources and offspring, pair bdnnoig, and concealed oivuolatn, went very much hand-in-hand over our evolution. We have also evolved a specialized psychology for forming long-term romantic relationships with the pslisioibty of investing in offspring together. We fall in love. All around the world, people prefer mates who are kind and generous and capable and willing to care for maets and offspring. In one of the lrsgaet cross-cultural studies of human mate pceenfreres ever conducted, covering 33 crnotueis shown in red here, the sgline most important mate choice ctierorin to both men and women, was mutual love and attraction. But as you also know, people are not always perfectly faithful to their mates. And in particular, women sometimes face a tradeoff between good genes and investment. Women sometimes find themselves in rliniohtpsaes with men who may be caring providers, but may not possess the best quality genes for offspring making them strong and hlteahy. And several ftraeeus of women's mating psychology seem to have evolved, in part, to resolve this trade off. And I mean, rtiucireng geens, if you will, from outside of the long-term relationship. For example, women have more sexual fantasies about men other than their long-term partner, during the fertile part of the cycle, and that's particularly true if the long-term partner has physical signs of being lower in genetic qlatiuy, like he's less physically attractive. I think that's ietrsitneng. (Laughter) That's why I'm talking about it, I hope you do too. And women's mate preferences similarly change over the cycle so that they prefer more dominant, more masculine males during the fertile part of the cycle. These are results of a study that I conducted on women's preferences for men's voices. And I used computer software to mapanltuie recordings of men's voices to make them sound either more masculine or more dominant, or more snouriatdbe, more feminine. And I had women rate them on how aiacrtttve would this man be for a short-term, purely sexual relationship, and for a long-term committed relationship? And I also got itnmofoarin about where women were in their cycles. Were they in the fertile or non-fertile part of the cycle? These were all women not taking hormonal contraception. And what I found was that women prrfeeerd a more msanuilce, dominant-sounding voice, specifically in the fertile point of the cycle, and only for a sexaul relationship versus a long-term committed rolnhtieisap. Now, this sounds like science fiction, but it's science, fact. Because this result has been shwon lots of temis across a variety of domains from women's preferences for men's voices, that this result was replicated by another lab. Women's preferences for men's faces, bodies, odors, and even behavior. Well, I said that we would get to orgasm. (Laughter) And we're there. I just want to start by saying I'm for it. (Laughter) I'm pro-orgasm. I think more people should have more orgasms. But from a scientific perspective, women's oargsm is especially fascinating because there's evidence indicating that it increases the probability that conception will result from an act of sex. There's evidence that it brings sperm up through the flmaee rpitevourdce tcart and toward the egg. And think about what the implications here could be. If woemn were more likely to have orgasms with some men than others, then this could be a mecihsnam by which they choose, not consciously, to be fieletrizd by some males and not others. And wouldn't you predict that women would be more likely to have orgasms with males of high genetic quality? And in fact, a study by my lab puhisbeld just a cuploe of years ago found that women reported more orgasms, earlier timed orgasms, that is, they were eeaisr to achieve, they achieved them more qlukciy, when they were having sex when their mate was more masculine and more dominant, and what's interesting is that this was true only for their osgamrs from sexual intercourse, but not from other partnered sexual behaviors. I'll let you use your igoamtinian what those might be. So we've seen that thinking like an evolutionist can enable us to predict things about ourselves that we did not already know, and would not likely have guessed for a long time. We didn't know that women's mate preferences changed over the ccyle. Until etonruiloavy thinking led us to that dvscieory. So that's one point that I want to make. But we've also seen how evolutionary thinking can cifraly and unite diverse parts of the human eeipncxere, and help us uasntnrded the best and the worst of ourselves, from violence and aggression and inditefliy to men's care for their children, sexual atairtoctn, sexual pleasure, and even the strength and frtiligay of rinmatoc love. Thank you. (Applause)

Open Cloze

Hi there. I could be wrong, but I think this talk may have the distinction of being the one talk in this series that ends with orgasm. (Laughter) But let's not get ahead of ourselves. (Laughter) Have you ever thought about the fact that you're here, alive on this ______ because every one of your ancestors reproduced? Every one, in an unbroken chain, all the way back to the first life on this planet, over three and a half billion years ago. That's a lot of reproducing. And for the past billion years, your ancestors reproduced ________. So sex is a pretty big deal. But you probably knew that. But let's talk about human mating. Why does human mating take the forms that it does? Why are we attracted to certain people? Why do we sometimes form long-term romantic relationships? Why do we sometimes cheat? Now I don't mean why consciously do we do these things. I don't mean what happens in the brain to cause it. I mean, why did we evolve these feelings and these _________? In other words, how did the __________ brain __________ and brain chemistry contribute to our ancestors' reproductive success so that those traits got ______ on into the present generation while others didn't. Answering evolutionary questions like this is like being a _____ scene ____________, we're left with the evidence, and we have to try to establish what happened. So let's go back six or seven million years ago to our early ancestors. This is right after the split between our lineage and the lineage that would eventually give rise to chimpanzees. Now these were small brained apes, they ______ on two legs, and males probably fought each other for mating opportunities. We know this because males fight for mates in all of our closest living _________, chimpanzees, orangutans, gorillas. And because males are larger than females when they fight for mates. And the fossil record indicates that our male ancestors were larger than females. So males tend to be ______, more ________, stronger, more physically aggressive, when they fight for mates. Our species has all the hallmarks of a species that's experienced an evolutionary history of male fighting for mates. For example, men have, on average, 60 percent more muscle mass, and 75 percent more upper body ______ mass, and those differences in musculature translate into large sex differences in strength. The average man is stronger than 99.9% of women. These are data on hand strength, which is a good predictor of overall _____ body strength, on over 600 men and women. And as you can see, there's a large sex difference. And in fact, not one of almost 400 women had as strong of a hand strength as the average man. So, men can open jars. (Laughter) And move furniture or at least two things that we're good for. Who cares, right? The answer is that men care. Men, especially _____ men, seem really concerned about figuring out who's the toughest or strongest, or the most physically formidable, and sometimes they devise elaborate ways for determining this. From early development, boys and men are more physically aggressive than girls and women all over the _____, and this __________ sometimes results in violence. Men have a _______ monopoly on same-sex homicides. In other words, men are vastly more likely to kill each other than women are to kill each other. These are data from every society from every time period in history for which data were available when the authors compiled them, on proportion of same-sex homicides that are male killing male. And as you can see, the percentage is always close to 100%. On average, 95% of same-sex homicides are _________ by males, and ___________, these don't _______ war killings, which would bring the percentages even closer to 100%. And from what evidence that we have, a dominance among men translates into mating and reproductive opportunities. So we're a species that's ___________ an evolutionary history in which our male _________ won mating _____________ through the use or threat of force. In that regard, our apple has not fallen far from the evolutionary tree. But in other ways, human mating and reproduction are profoundly different from what we see in our close relatives, and they've changed a lot since our early ancestors. For example, males in chimpanzees, __________ and ________, spend time and effort _________ for mates, but don't _____ much time with individual females and don't provide resources. They don't provide food for their offspring. So that's a big change. Although most human societies allow polygamous marriage, that is one man married to more than one woman, even within polygamous societies, most marriages are monogamous. And in the _______ hunter-gatherer _______, almost 80% of _______ women are __________, so that's different. And, importantly, men provide resources for their mates and offspring. So how did we get there? Well, in species where males fight each other for mates, dominant males indicated by the larger, darker male symbols here, tend to have more mating opportunities, and hence more offspring. And subordinate males tend to have fewer mating opportunities and are more likely to fail to reproduce. So this sets up an interesting situation, because for subordinate males, it would be advantageous to attempt ________ rather than _______ lots of mating opportunities. One mate is better than none. The problem is that in _______, subordinate males cannot defend females from dominant males, and besides, females tend to prefer mating with dominant _____ for the genetic benefits, producing stronger, healthier _________. So what changed all of this was probably several ___________ happening together around the same time. By about two and a half million years ago, we had started to incorporate more meat into our diet. We know this from various _____ of evidence, including - this is cool - stone tool cut marks on animal _____ dated to 2.5 million years ago. That's cool. I love this stuff! And then by about 2 _______ _____ ago, brain size really started to ________, and with that came a ___________ of the juvenile period, so now kids became both really costly and costly for a long period of time. And this made male provisioning both possible and necessary. Possible because it's much easier to bring back calories, _______, fats, in the form of meat than trying to do that by ____________ plant _____, and necessary because kids became so energetically costly that individual females would have had trouble providing resources for themselves and their offspring. And when we look at modern hunter-gatherer societies, that's what we see. These are aggregate data across several hunter-gatherer _________ on net daily calories. Are you bringing in more calories than you consume, through foraging, or are you consuming more than you bring in? And the green bars are net daily caloric surplus, in other _____, ________ in more than you consume. And the red bars are a deficit, so you're consuming more than you bring in. And you'll notice that men from about 20 years of age to 60 years of age are operating at a daily _______ surplus. They _____ in, generally through hunting, more ________ than they can _______, and these calories are distributed. If it's large game, it's generally distributed equally to everybody in the village or camp. _______ items can be brought back to individual family, but this contrasts with what's going on with women, in their reproductive years, they're operating at a daily caloric deficit. _________, lactation, carrying babies, are extremely costly energetically and _____ one's ability to forage efficiently. So male provisioning, both possible through hunting, and necessary. And this change had profound impacts on human mating and reproduction. In a sense, it ______ the _______ for females. So now it was sometimes _____ mating with a subordinate male, even if he may not possess the best genes, if he provided resources. And this is baboon pornography. (Laughter) I probably should have warned you there'd be monkey porn. This is from PlayBaboon Magazine. Alright, I'm going to stop with the jokes. This is a female baboon in estrus, so her genitals are swollen, and this happens in a lot of _______ species. Females' appearance changes over the cycle, and becomes more attractive and this incites male competition for _______ during the _______ part of the cycle, with dominant males tending to monopolize ___________, closer to ovulation. Well. We don't look like this. And you knew that. But what you might not know is that women's attractiveness does change over the cycle. My lab, and others, have shown that women's faces, voices, even odors, are more attractive to men during the fertile part of the cycle. But these changes are extremely subtle. And ________ to other primates, the evidence indicates that we've evolved to suppress cues to ovulation. That in a sense, ovulation is concealed in humans. But think about what impact this would have. This would mean that dominant males would not be able to monopolize copulations near ovulation. It would protect the pair bond from invasion by a dominant male. So that a male in a pair would have more confidence that he was the ______ of the offspring. The couple is having sex throughout the cycle. And this is unique to human ______, we don't see it in many other primates. We have sex throughout the cycle. And so this would essentially increase a male's confidence in paternity, because a dominant or some other male wouldn't be able to target the female and bully their way in at the fertile point in the cycle. And this would have important implications for parental __________, in particular, males providing resources for their offspring. Because across _______, when males provide resources for offspring, they target those resources toward their own biological offspring, and they avoid investing in the offspring of unrelated males. And so the evolution of male care for offspring and investing in resources and offspring, pair _______, and concealed _________, went very much hand-in-hand over our evolution. We have also evolved a specialized psychology for forming long-term romantic relationships with the ___________ of investing in offspring together. We fall in love. All around the world, people prefer mates who are kind and generous and capable and willing to care for _____ and offspring. In one of the _______ cross-cultural studies of human mate ___________ ever conducted, covering 33 _________ shown in red here, the ______ most important mate choice _________ to both men and women, was mutual love and attraction. But as you also know, people are not always perfectly faithful to their mates. And in particular, women sometimes face a tradeoff between good genes and investment. Women sometimes find themselves in _____________ with men who may be caring providers, but may not possess the best quality genes for offspring making them strong and _______. And several ________ of women's mating psychology seem to have evolved, in part, to resolve this trade off. And I mean, __________ _____, if you will, from outside of the long-term relationship. For example, women have more sexual fantasies about men other than their long-term partner, during the fertile part of the cycle, and that's particularly true if the long-term partner has physical signs of being lower in genetic _______, like he's less physically attractive. I think that's ___________. (Laughter) That's why I'm talking about it, I hope you do too. And women's mate preferences similarly change over the cycle so that they prefer more dominant, more masculine males during the fertile part of the cycle. These are results of a study that I conducted on women's preferences for men's voices. And I used computer software to __________ recordings of men's voices to make them sound either more masculine or more dominant, or more ___________, more feminine. And I had women rate them on how __________ would this man be for a short-term, purely sexual relationship, and for a long-term committed relationship? And I also got ___________ about where women were in their cycles. Were they in the fertile or non-fertile part of the cycle? These were all women not taking hormonal contraception. And what I found was that women _________ a more _________, dominant-sounding voice, specifically in the fertile point of the cycle, and only for a ______ relationship versus a long-term committed ____________. Now, this sounds like science fiction, but it's science, fact. Because this result has been _____ lots of _____ across a variety of domains from women's preferences for men's voices, that this result was replicated by another lab. Women's preferences for men's faces, bodies, odors, and even behavior. Well, I said that we would get to orgasm. (Laughter) And we're there. I just want to start by saying I'm for it. (Laughter) I'm pro-orgasm. I think more people should have more orgasms. But from a scientific perspective, women's ______ is especially fascinating because there's evidence indicating that it increases the probability that conception will result from an act of sex. There's evidence that it brings sperm up through the ______ ____________ _____ and toward the egg. And think about what the implications here could be. If _____ were more likely to have orgasms with some men than others, then this could be a _________ by which they choose, not consciously, to be __________ by some males and not others. And wouldn't you predict that women would be more likely to have orgasms with males of high genetic quality? And in fact, a study by my lab _________ just a ______ of years ago found that women reported more orgasms, earlier timed orgasms, that is, they were ______ to achieve, they achieved them more _______, when they were having sex when their mate was more masculine and more dominant, and what's interesting is that this was true only for their _______ from sexual intercourse, but not from other partnered sexual behaviors. I'll let you use your ___________ what those might be. So we've seen that thinking like an evolutionist can enable us to predict things about ourselves that we did not already know, and would not likely have guessed for a long time. We didn't know that women's mate preferences changed over the _____. Until ____________ thinking led us to that _________. So that's one point that I want to make. But we've also seen how evolutionary thinking can _______ and unite diverse parts of the human __________, and help us __________ the best and the worst of ourselves, from violence and aggression and __________ to men's care for their children, sexual __________, sexual pleasure, and even the strength and _________ of ________ love. Thank you. (Applause)

Solution

  1. interesting
  2. muscle
  3. relationships
  4. single
  5. importantly
  6. sexual
  7. bringing
  8. young
  9. larger
  10. societies
  11. recruiting
  12. words
  13. consume
  14. experienced
  15. married
  16. species
  17. shown
  18. years
  19. preferences
  20. possibility
  21. ovulation
  22. discovery
  23. genes
  24. orangutans
  25. general
  26. worth
  27. tipped
  28. father
  29. monogamy
  30. countries
  31. transporting
  32. experience
  33. muscular
  34. information
  35. romantic
  36. calories
  37. primate
  38. world
  39. investigator
  40. published
  41. society
  42. committed
  43. healthy
  44. attractive
  45. lengthening
  46. bring
  47. criterion
  48. understand
  49. mating
  50. smaller
  51. planet
  52. monogamous
  53. winning
  54. upper
  55. relatives
  56. attraction
  57. increase
  58. caloric
  59. bones
  60. quality
  61. crime
  62. opportunities
  63. features
  64. foods
  65. quickly
  66. fertilized
  67. largest
  68. walked
  69. fragility
  70. tract
  71. clarify
  72. gorillas
  73. females
  74. ancestors
  75. million
  76. women
  77. times
  78. gestation
  79. spend
  80. orgasm
  81. balance
  82. underlying
  83. subordinate
  84. compared
  85. behaviors
  86. competing
  87. evolutionary
  88. aggression
  89. investment
  90. bonding
  91. fertile
  92. preferred
  93. reproductive
  94. mates
  95. lines
  96. relationship
  97. orgasms
  98. cycle
  99. passed
  100. limit
  101. female
  102. copulations
  103. protein
  104. sexually
  105. males
  106. imagination
  107. infidelity
  108. transitions
  109. manipulate
  110. easier
  111. include
  112. mechanism
  113. couple
  114. masculine
  115. offspring
  116. structures
  117. virtual
  118. average

Original Text

Hi there. I could be wrong, but I think this talk may have the distinction of being the one talk in this series that ends with orgasm. (Laughter) But let's not get ahead of ourselves. (Laughter) Have you ever thought about the fact that you're here, alive on this planet because every one of your ancestors reproduced? Every one, in an unbroken chain, all the way back to the first life on this planet, over three and a half billion years ago. That's a lot of reproducing. And for the past billion years, your ancestors reproduced sexually. So sex is a pretty big deal. But you probably knew that. But let's talk about human mating. Why does human mating take the forms that it does? Why are we attracted to certain people? Why do we sometimes form long-term romantic relationships? Why do we sometimes cheat? Now I don't mean why consciously do we do these things. I don't mean what happens in the brain to cause it. I mean, why did we evolve these feelings and these behaviors? In other words, how did the underlying brain structures and brain chemistry contribute to our ancestors' reproductive success so that those traits got passed on into the present generation while others didn't. Answering evolutionary questions like this is like being a crime scene investigator, we're left with the evidence, and we have to try to establish what happened. So let's go back six or seven million years ago to our early ancestors. This is right after the split between our lineage and the lineage that would eventually give rise to chimpanzees. Now these were small brained apes, they walked on two legs, and males probably fought each other for mating opportunities. We know this because males fight for mates in all of our closest living relatives, chimpanzees, orangutans, gorillas. And because males are larger than females when they fight for mates. And the fossil record indicates that our male ancestors were larger than females. So males tend to be larger, more muscular, stronger, more physically aggressive, when they fight for mates. Our species has all the hallmarks of a species that's experienced an evolutionary history of male fighting for mates. For example, men have, on average, 60 percent more muscle mass, and 75 percent more upper body muscle mass, and those differences in musculature translate into large sex differences in strength. The average man is stronger than 99.9% of women. These are data on hand strength, which is a good predictor of overall upper body strength, on over 600 men and women. And as you can see, there's a large sex difference. And in fact, not one of almost 400 women had as strong of a hand strength as the average man. So, men can open jars. (Laughter) And move furniture or at least two things that we're good for. Who cares, right? The answer is that men care. Men, especially young men, seem really concerned about figuring out who's the toughest or strongest, or the most physically formidable, and sometimes they devise elaborate ways for determining this. From early development, boys and men are more physically aggressive than girls and women all over the world, and this aggression sometimes results in violence. Men have a virtual monopoly on same-sex homicides. In other words, men are vastly more likely to kill each other than women are to kill each other. These are data from every society from every time period in history for which data were available when the authors compiled them, on proportion of same-sex homicides that are male killing male. And as you can see, the percentage is always close to 100%. On average, 95% of same-sex homicides are committed by males, and importantly, these don't include war killings, which would bring the percentages even closer to 100%. And from what evidence that we have, a dominance among men translates into mating and reproductive opportunities. So we're a species that's experienced an evolutionary history in which our male ancestors won mating opportunities through the use or threat of force. In that regard, our apple has not fallen far from the evolutionary tree. But in other ways, human mating and reproduction are profoundly different from what we see in our close relatives, and they've changed a lot since our early ancestors. For example, males in chimpanzees, orangutans and gorillas, spend time and effort competing for mates, but don't spend much time with individual females and don't provide resources. They don't provide food for their offspring. So that's a big change. Although most human societies allow polygamous marriage, that is one man married to more than one woman, even within polygamous societies, most marriages are monogamous. And in the average hunter-gatherer society, almost 80% of married women are monogamous, so that's different. And, importantly, men provide resources for their mates and offspring. So how did we get there? Well, in species where males fight each other for mates, dominant males indicated by the larger, darker male symbols here, tend to have more mating opportunities, and hence more offspring. And subordinate males tend to have fewer mating opportunities and are more likely to fail to reproduce. So this sets up an interesting situation, because for subordinate males, it would be advantageous to attempt monogamy rather than winning lots of mating opportunities. One mate is better than none. The problem is that in general, subordinate males cannot defend females from dominant males, and besides, females tend to prefer mating with dominant males for the genetic benefits, producing stronger, healthier offspring. So what changed all of this was probably several transitions happening together around the same time. By about two and a half million years ago, we had started to incorporate more meat into our diet. We know this from various lines of evidence, including - this is cool - stone tool cut marks on animal bones dated to 2.5 million years ago. That's cool. I love this stuff! And then by about 2 million years ago, brain size really started to increase, and with that came a lengthening of the juvenile period, so now kids became both really costly and costly for a long period of time. And this made male provisioning both possible and necessary. Possible because it's much easier to bring back calories, protein, fats, in the form of meat than trying to do that by transporting plant foods, and necessary because kids became so energetically costly that individual females would have had trouble providing resources for themselves and their offspring. And when we look at modern hunter-gatherer societies, that's what we see. These are aggregate data across several hunter-gatherer societies on net daily calories. Are you bringing in more calories than you consume, through foraging, or are you consuming more than you bring in? And the green bars are net daily caloric surplus, in other words, bringing in more than you consume. And the red bars are a deficit, so you're consuming more than you bring in. And you'll notice that men from about 20 years of age to 60 years of age are operating at a daily caloric surplus. They bring in, generally through hunting, more calories than they can consume, and these calories are distributed. If it's large game, it's generally distributed equally to everybody in the village or camp. Smaller items can be brought back to individual family, but this contrasts with what's going on with women, in their reproductive years, they're operating at a daily caloric deficit. Gestation, lactation, carrying babies, are extremely costly energetically and limit one's ability to forage efficiently. So male provisioning, both possible through hunting, and necessary. And this change had profound impacts on human mating and reproduction. In a sense, it tipped the balance for females. So now it was sometimes worth mating with a subordinate male, even if he may not possess the best genes, if he provided resources. And this is baboon pornography. (Laughter) I probably should have warned you there'd be monkey porn. This is from PlayBaboon Magazine. Alright, I'm going to stop with the jokes. This is a female baboon in estrus, so her genitals are swollen, and this happens in a lot of primate species. Females' appearance changes over the cycle, and becomes more attractive and this incites male competition for females during the fertile part of the cycle, with dominant males tending to monopolize copulations, closer to ovulation. Well. We don't look like this. And you knew that. But what you might not know is that women's attractiveness does change over the cycle. My lab, and others, have shown that women's faces, voices, even odors, are more attractive to men during the fertile part of the cycle. But these changes are extremely subtle. And compared to other primates, the evidence indicates that we've evolved to suppress cues to ovulation. That in a sense, ovulation is concealed in humans. But think about what impact this would have. This would mean that dominant males would not be able to monopolize copulations near ovulation. It would protect the pair bond from invasion by a dominant male. So that a male in a pair would have more confidence that he was the father of the offspring. The couple is having sex throughout the cycle. And this is unique to human mating, we don't see it in many other primates. We have sex throughout the cycle. And so this would essentially increase a male's confidence in paternity, because a dominant or some other male wouldn't be able to target the female and bully their way in at the fertile point in the cycle. And this would have important implications for parental investment, in particular, males providing resources for their offspring. Because across species, when males provide resources for offspring, they target those resources toward their own biological offspring, and they avoid investing in the offspring of unrelated males. And so the evolution of male care for offspring and investing in resources and offspring, pair bonding, and concealed ovulation, went very much hand-in-hand over our evolution. We have also evolved a specialized psychology for forming long-term romantic relationships with the possibility of investing in offspring together. We fall in love. All around the world, people prefer mates who are kind and generous and capable and willing to care for mates and offspring. In one of the largest cross-cultural studies of human mate preferences ever conducted, covering 33 countries shown in red here, the single most important mate choice criterion to both men and women, was mutual love and attraction. But as you also know, people are not always perfectly faithful to their mates. And in particular, women sometimes face a tradeoff between good genes and investment. Women sometimes find themselves in relationships with men who may be caring providers, but may not possess the best quality genes for offspring making them strong and healthy. And several features of women's mating psychology seem to have evolved, in part, to resolve this trade off. And I mean, recruiting genes, if you will, from outside of the long-term relationship. For example, women have more sexual fantasies about men other than their long-term partner, during the fertile part of the cycle, and that's particularly true if the long-term partner has physical signs of being lower in genetic quality, like he's less physically attractive. I think that's interesting. (Laughter) That's why I'm talking about it, I hope you do too. And women's mate preferences similarly change over the cycle so that they prefer more dominant, more masculine males during the fertile part of the cycle. These are results of a study that I conducted on women's preferences for men's voices. And I used computer software to manipulate recordings of men's voices to make them sound either more masculine or more dominant, or more subordinate, more feminine. And I had women rate them on how attractive would this man be for a short-term, purely sexual relationship, and for a long-term committed relationship? And I also got information about where women were in their cycles. Were they in the fertile or non-fertile part of the cycle? These were all women not taking hormonal contraception. And what I found was that women preferred a more masculine, dominant-sounding voice, specifically in the fertile point of the cycle, and only for a sexual relationship versus a long-term committed relationship. Now, this sounds like science fiction, but it's science, fact. Because this result has been shown lots of times across a variety of domains from women's preferences for men's voices, that this result was replicated by another lab. Women's preferences for men's faces, bodies, odors, and even behavior. Well, I said that we would get to orgasm. (Laughter) And we're there. I just want to start by saying I'm for it. (Laughter) I'm pro-orgasm. I think more people should have more orgasms. But from a scientific perspective, women's orgasm is especially fascinating because there's evidence indicating that it increases the probability that conception will result from an act of sex. There's evidence that it brings sperm up through the female reproductive tract and toward the egg. And think about what the implications here could be. If women were more likely to have orgasms with some men than others, then this could be a mechanism by which they choose, not consciously, to be fertilized by some males and not others. And wouldn't you predict that women would be more likely to have orgasms with males of high genetic quality? And in fact, a study by my lab published just a couple of years ago found that women reported more orgasms, earlier timed orgasms, that is, they were easier to achieve, they achieved them more quickly, when they were having sex when their mate was more masculine and more dominant, and what's interesting is that this was true only for their orgasms from sexual intercourse, but not from other partnered sexual behaviors. I'll let you use your imagination what those might be. So we've seen that thinking like an evolutionist can enable us to predict things about ourselves that we did not already know, and would not likely have guessed for a long time. We didn't know that women's mate preferences changed over the cycle. Until evolutionary thinking led us to that discovery. So that's one point that I want to make. But we've also seen how evolutionary thinking can clarify and unite diverse parts of the human experience, and help us understand the best and the worst of ourselves, from violence and aggression and infidelity to men's care for their children, sexual attraction, sexual pleasure, and even the strength and fragility of romantic love. Thank you. (Applause)

Frequently Occurring Word Combinations

ngrams of length 2

collocation frequency
human mating 4
million years 4
mating opportunities 4
dominant males 4
fertile part 4
provide resources 3
daily caloric 3
mate preferences 3
early ancestors 2
males fight 2
male ancestors 2
males tend 2
evolutionary history 2
upper body 2
large sex 2
average man 2
individual females 2
subordinate males 2
providing resources 2
net daily 2
fertile point 2
evolutionary thinking 2

Important Words

  1. ability
  2. achieve
  3. achieved
  4. act
  5. advantageous
  6. age
  7. aggregate
  8. aggression
  9. aggressive
  10. alive
  11. alright
  12. ancestors
  13. animal
  14. answer
  15. answering
  16. apes
  17. appearance
  18. applause
  19. apple
  20. attempt
  21. attracted
  22. attraction
  23. attractive
  24. attractiveness
  25. authors
  26. average
  27. avoid
  28. babies
  29. baboon
  30. balance
  31. bars
  32. behavior
  33. behaviors
  34. benefits
  35. big
  36. billion
  37. biological
  38. bodies
  39. body
  40. bond
  41. bonding
  42. bones
  43. boys
  44. brain
  45. brained
  46. bring
  47. bringing
  48. brings
  49. brought
  50. bully
  51. caloric
  52. calories
  53. camp
  54. capable
  55. care
  56. cares
  57. caring
  58. carrying
  59. chain
  60. change
  61. changed
  62. cheat
  63. chemistry
  64. children
  65. chimpanzees
  66. choice
  67. choose
  68. clarify
  69. close
  70. closer
  71. closest
  72. committed
  73. compared
  74. competing
  75. competition
  76. compiled
  77. computer
  78. concealed
  79. conception
  80. concerned
  81. conducted
  82. confidence
  83. consciously
  84. consume
  85. consuming
  86. contraception
  87. contrasts
  88. contribute
  89. cool
  90. copulations
  91. costly
  92. countries
  93. couple
  94. covering
  95. crime
  96. criterion
  97. cues
  98. cut
  99. cycle
  100. cycles
  101. daily
  102. darker
  103. data
  104. dated
  105. deal
  106. defend
  107. deficit
  108. determining
  109. development
  110. devise
  111. diet
  112. difference
  113. differences
  114. discovery
  115. distinction
  116. distributed
  117. diverse
  118. domains
  119. dominance
  120. dominant
  121. earlier
  122. early
  123. easier
  124. efficiently
  125. effort
  126. egg
  127. elaborate
  128. enable
  129. ends
  130. energetically
  131. equally
  132. essentially
  133. establish
  134. estrus
  135. eventually
  136. evidence
  137. evolution
  138. evolutionary
  139. evolutionist
  140. evolve
  141. evolved
  142. experience
  143. experienced
  144. extremely
  145. face
  146. faces
  147. fact
  148. fail
  149. faithful
  150. fall
  151. fallen
  152. family
  153. fantasies
  154. fascinating
  155. father
  156. fats
  157. features
  158. feelings
  159. female
  160. females
  161. feminine
  162. fertile
  163. fertilized
  164. fiction
  165. fight
  166. fighting
  167. figuring
  168. find
  169. food
  170. foods
  171. forage
  172. foraging
  173. force
  174. form
  175. formidable
  176. forming
  177. forms
  178. fossil
  179. fought
  180. fragility
  181. furniture
  182. game
  183. general
  184. generally
  185. generation
  186. generous
  187. genes
  188. genetic
  189. genitals
  190. gestation
  191. girls
  192. give
  193. good
  194. gorillas
  195. green
  196. guessed
  197. hallmarks
  198. hand
  199. happened
  200. happening
  201. healthier
  202. healthy
  203. high
  204. history
  205. homicides
  206. hope
  207. hormonal
  208. human
  209. humans
  210. hunting
  211. imagination
  212. impact
  213. impacts
  214. implications
  215. important
  216. importantly
  217. incites
  218. include
  219. including
  220. incorporate
  221. increase
  222. increases
  223. indicating
  224. individual
  225. infidelity
  226. information
  227. intercourse
  228. interesting
  229. invasion
  230. investigator
  231. investing
  232. investment
  233. items
  234. jars
  235. jokes
  236. juvenile
  237. kids
  238. kill
  239. killing
  240. killings
  241. kind
  242. knew
  243. lab
  244. lactation
  245. large
  246. larger
  247. largest
  248. laughter
  249. led
  250. left
  251. legs
  252. lengthening
  253. life
  254. limit
  255. lineage
  256. lines
  257. living
  258. long
  259. lot
  260. lots
  261. love
  262. magazine
  263. making
  264. male
  265. males
  266. man
  267. manipulate
  268. marks
  269. marriage
  270. marriages
  271. married
  272. masculine
  273. mass
  274. mate
  275. mates
  276. mating
  277. meat
  278. mechanism
  279. men
  280. million
  281. modern
  282. monkey
  283. monogamous
  284. monogamy
  285. monopolize
  286. monopoly
  287. move
  288. muscle
  289. muscular
  290. musculature
  291. mutual
  292. net
  293. notice
  294. odors
  295. offspring
  296. open
  297. operating
  298. opportunities
  299. orangutans
  300. orgasm
  301. orgasms
  302. ovulation
  303. pair
  304. parental
  305. part
  306. partner
  307. partnered
  308. parts
  309. passed
  310. paternity
  311. people
  312. percent
  313. percentage
  314. percentages
  315. perfectly
  316. period
  317. perspective
  318. physical
  319. physically
  320. planet
  321. plant
  322. playbaboon
  323. pleasure
  324. point
  325. polygamous
  326. porn
  327. pornography
  328. possess
  329. possibility
  330. predict
  331. predictor
  332. prefer
  333. preferences
  334. preferred
  335. present
  336. pretty
  337. primate
  338. primates
  339. probability
  340. problem
  341. producing
  342. profound
  343. profoundly
  344. proportion
  345. protect
  346. protein
  347. provide
  348. providers
  349. providing
  350. provisioning
  351. psychology
  352. published
  353. purely
  354. quality
  355. questions
  356. quickly
  357. rate
  358. record
  359. recordings
  360. recruiting
  361. red
  362. regard
  363. relationship
  364. relationships
  365. relatives
  366. replicated
  367. reported
  368. reproduce
  369. reproduced
  370. reproducing
  371. reproduction
  372. reproductive
  373. resolve
  374. resources
  375. result
  376. results
  377. rise
  378. romantic
  379. scene
  380. science
  381. scientific
  382. sense
  383. series
  384. sets
  385. sex
  386. sexual
  387. sexually
  388. shown
  389. signs
  390. similarly
  391. single
  392. situation
  393. size
  394. small
  395. smaller
  396. societies
  397. society
  398. software
  399. sound
  400. sounds
  401. specialized
  402. species
  403. specifically
  404. spend
  405. sperm
  406. split
  407. start
  408. started
  409. stone
  410. stop
  411. strength
  412. strong
  413. stronger
  414. strongest
  415. structures
  416. studies
  417. study
  418. subordinate
  419. subtle
  420. success
  421. suppress
  422. surplus
  423. swollen
  424. symbols
  425. talk
  426. talking
  427. target
  428. tend
  429. tending
  430. thinking
  431. thought
  432. threat
  433. time
  434. timed
  435. times
  436. tipped
  437. tool
  438. toughest
  439. tract
  440. trade
  441. tradeoff
  442. traits
  443. transitions
  444. translate
  445. translates
  446. transporting
  447. tree
  448. trouble
  449. true
  450. unbroken
  451. underlying
  452. understand
  453. unique
  454. unite
  455. unrelated
  456. upper
  457. variety
  458. vastly
  459. village
  460. violence
  461. virtual
  462. voice
  463. voices
  464. walked
  465. war
  466. warned
  467. ways
  468. winning
  469. woman
  470. women
  471. won
  472. words
  473. world
  474. worst
  475. worth
  476. wrong
  477. years
  478. young