Michelle: A study asked men and women a simple question: How many sexual partners would you ideally want in your lifetime? Women, on average, said about four or five. Men? Eighteen. Mark: Eighteen! Whoa. That's... ambitious. And also a little bit terrifying. Where does a number like that even come from? Michelle: It comes from the deep, often invisible logic of our evolutionary past. That staggering difference isn't just a quirk—it's a clue to a hidden evolutionary script we're all following. And it’s exactly what we're exploring today through David M. Buss's landmark book, Strategies of Human Mating. Mark: David M. Buss. I've heard that name. He’s a big deal in this field, right? Michelle: He's one of the founders of evolutionary psychology. And this book was revolutionary because it was based on a massive, unprecedented study of over 10,000 people in 37 different cultures, from the Zulus in South Africa to Brazilians to Estonians. He wanted to create the first truly scientific, cross-cultural map of human desire. Mark: So he went out to prove we're all just animals operating on instinct. I can already feel people getting defensive. Michelle: Well, his work is definitely polarizing for that very reason. But to understand that 18-to-4.5 difference, we have to start where he did: with a puzzle that drove Charles Darwin crazy.

Mark: A puzzle that stumped Darwin? Okay, I'm listening. Michelle: It was the peacock's tail. Darwin’s theory of natural selection was all about survival of the fittest. Traits evolve because they help an organism survive and reproduce. But the peacock's tail does the opposite. It's heavy, it's cumbersome, and it's basically a giant, shimmering "EAT ME" sign for predators. It made no sense. Mark: Right, it's like wearing a neon-green tuxedo to a spy convention. It's a liability. Michelle: Exactly. Until Darwin had a breakthrough. He realized there's another force at play: sexual selection. Some traits don't evolve for survival; they evolve because they give you a mating advantage. The peacock's tail, as costly as it is, evolved for one reason: peahens dig it. They find it irresistibly attractive. Mark: So the females' desires literally shaped the males' evolution. That's one form of sexual selection, called intersexual selection—or female choice. Michelle: Precisely. Then there's the other side of the coin: intrasexual competition. Think of male elephant seals. They're these 4,000-pound behemoths, four times the size of the females. Why? Because they fight each other in brutal, bloody battles for control of a harem. The biggest, strongest male wins, gets to mate with dozens of females, and passes on his genes for size and aggression. The smaller guys get nothing. Mark: Okay, peacocks and seals are great, but how does this apply to humans swiping on a dating app or meeting in a coffee shop? We're not usually fighting to the death on a beach for a date. At least, not on the first date. Michelle: That's the perfect question, and it leads to the most important concept in the whole book: Parental Investment Theory, developed by Robert Trivers in the 70s. This is the master key that unlocks human mating. Mark: Parental Investment. Sounds like a 529 college savings plan. Michelle: It's kind of like an evolutionary down payment. Trivers's theory is simple but profound: the sex that invests more in offspring will be the more selective, or 'choosy,' sex. The sex that invests less will be more competitive for access to the high-investing sex. Mark: And for humans, the minimum investment is wildly different. Michelle: Wildly. For a woman, the absolute minimum investment is nine months of pregnancy, the dangers of childbirth, and then typically a long period of lactation and care. It's a massive biological cost. For a man, the minimum investment can be… well, a few minutes. Mark: I see where this is going. So it's an evolutionary ROI calculation. Women have a much higher 'cost per child,' so they've evolved to be incredibly careful shoppers. Men's cost can be very low, so they've evolved to play the numbers game. Michelle: You've got it. That's the fundamental logic. And that careful shopping versus playing the numbers game explains why our mating 'menus' look so different.

Mark: The mating menu. I like that. So what's on the menu when we're looking for something serious, for a long-term partner? Michelle: This is where Buss's 37-culture study is so powerful. He asked people everywhere to rate the importance of different qualities in a long-term mate. And the patterns were stunningly consistent across the globe. Mark: Let me guess. Men want someone attractive and women want someone with a good job. Michelle: That’s the headline, and it's remarkably accurate. Across all 37 cultures, women placed a significantly higher value on a partner's financial prospects, social status, and ambition. They desired men who could provide resources. Mark: Okay, but hold on. That sounds incredibly stereotypical and, frankly, a bit offensive in 2024. Are we really saying women are just evolved gold-diggers? Critics must have a field day with this. Michelle: They do. This is easily the most controversial part of the book, and it's often accused of biological determinism. But Buss's argument is that these aren't moral judgments, they're adaptive preferences that solved real survival problems for our ancestors. For an ancestral woman, a partner with resources, or the ambition to get them, wasn't a luxury—it was a life-or-death ticket for her and her children. It meant food, protection, and a better chance of survival. Mark: So it's not about wanting a sports car, it's about an ancient program that equates resources with stability and safety for offspring. Michelle: Exactly. And for men? Their 'shopping list' for a long-term partner was just as consistent. Universally, men valued physical attractiveness and youth more than women did. Mark: The other side of the stereotype: men are just shallow. Michelle: Again, Buss reframes this. He argues that 'beauty' isn't arbitrary. It's a collection of cues that signal youth, health, and, most importantly, fertility. Things like clear skin, bright eyes, full lips, and a certain waist-to-hip ratio are all reliable, observable indicators of a woman's reproductive value. An ancestral man who chose partners based on these cues was more likely to have successful offspring. Mark: So our standards of beauty are basically just an ancient fertility checklist running in our subconscious. That's... a deeply unromantic way to look at love. Michelle: It can feel that way. But what's fascinating is how this entire menu flips when you change the context from long-term to short-term mating. Mark: Ah, back to the 18 partners. Michelle: Back to the 18 partners. For short-term flings, the data shows men dramatically lower their standards on almost everything—except willingness. The desire for sexual variety is the biggest psychological sex difference Buss found. And it's not just what people say. There was a famous study by Clarke and Hatfield where experimenters approached strangers on a college campus. Mark: I think I've heard of this one. Michelle: They'd say, "I find you very attractive," and then ask one of three questions. "Would you go on a date with me?" About 50% of both men and women said yes. "Would you come back to my apartment?" 69% of men said yes, but only 6% of women. Mark: And the last question... Michelle: "Would you have sex with me?" 75% of the men said yes. And the number of women who said yes? Zero. Not one. Mark: Zero! That is a canyon of a difference. It shows that the parental investment risk is always there for women, even in a casual context, so the answer is almost always no. For men, the potential upside is high and the cost is low, so the answer is often yes. Michelle: Precisely. The strategies are fundamentally different because the biological stakes are different. And when you have these conflicting strategies playing out in the same mating pool, it's a perfect recipe for conflict, competition, and what Buss calls the 'dark arts' of mating.

Mark: The dark arts. This sounds like where things get messy. Michelle: They do. Let's start with mate poaching. That’s the official term for trying to lure someone who is already in a romantic relationship. Mark: I feel like everyone has either done this or had it done to them. How common is it really? Michelle: Shockingly common. In one of Buss's studies, about 60% of men and 53% of women admitted they have tried to poach someone for a long-term relationship. It's a viable, if risky, mating strategy. Someone already in a relationship has been 'pre-vetted'—you know they have the qualities to attract and keep a mate. Mark: It's like buying a certified pre-owned car. Someone else already kicked the tires for you. But if poaching is the offense, what's the defense? Michelle: The defense is mate guarding. And the primary emotion that powers our mate-guarding system is jealousy. Buss argues that jealousy isn't a character flaw or a sign of immaturity. It's an evolved alarm system designed to protect your relationship from threats. Mark: A security system. I like that. But does the alarm go off for the same reasons for men and women? Michelle: Absolutely not. And this is another one of the book's most powerful findings. The triggers are completely different, and it goes right back to those core adaptive problems. For a man, the biggest reproductive threat throughout history was paternity uncertainty. He could never be 100% sure a child was his. Mark: Right. "Mama's baby, papa's maybe." Michelle: Exactly. So, for men, the jealousy alarm is tuned to one thing above all else: sexual infidelity. The thought of his partner having sex with another man is the ultimate betrayal because it threatens the core of his reproductive success. Mark: And for women? She always knows the child is hers, so what's her biggest threat? Michelle: The loss of her partner's investment. His time, his resources, his commitment, his protection. If he diverts all of that to another woman and her children, her own survival and her children's survival are at risk. So, her jealousy alarm is tuned to emotional infidelity. Mark: So the idea of her partner falling in love with someone else is the ultimate threat. Michelle: Precisely. Buss tested this with a stark choice: Imagine your partner having a passionate, one-time sexual affair, or imagine them forming a deep, emotional, non-sexual bond with someone else. Which distresses you more? Mark: And the results followed the theory? Michelle: Perfectly. Across cultures, a strong majority of men said the sexual infidelity was worse. And an overwhelming majority of women—something like 87% in the U.S. sample—said the emotional infidelity was worse. Mark: Wow. That explains so much about common relationship conflicts. The classic fight that starts with "Who were you texting?" versus the one that starts with "Did you sleep with them?" It's the same ancient alarm system, just calibrated to detect different threats. Michelle: It’s the same security system, but one is a motion detector and the other is a smoke alarm. They're both designed for protection, but they're triggered by very different things.

Mark: So when you put it all together—the peacocks, the parental investment, the different menus, the poaching—it paints a pretty intense picture of human relationships. Michelle: It does. What David Buss gives us in Strategies of Human Mating is this powerful, if sometimes unsettling, lens. Our modern dating lives, our swipes on an app, our feelings of jealousy, our deepest attractions—they aren't random. They're echoes of ancient adaptive problems our ancestors had to solve just to ensure we would be here today. Mark: I think the key thing to remember, and you touched on this, is that this isn't about justifying behavior. Explaining why men might be more prone to desire variety isn't an excuse for cheating. Michelle: Not at all. Buss is very clear on this. This is about understanding the source code, not validating the output. Knowing the underlying programming allows us to be more conscious of our impulses, to understand our partners better, and maybe even to navigate our relationships with a bit more wisdom and empathy. Mark: It definitely makes you look at your own relationships differently. It forces you to ask: Is this feeling me, or is it my ancient programming running in the background? It’s a profound question to sit with. Michelle: It really is. And it makes you wonder how these ancient strategies are playing out in our hyper-modern world of dating apps and social media. Mark: A topic for another day, perhaps. This has been fascinating, and a little bit humbling. Michelle: We agree. And we'd love to hear what you think. Does this resonate with your own experiences? Does it feel true, or does it feel like a reductive 'just-so' story? Let us know your thoughts on our social channels. We're always curious to hear how these ideas land. Mark: This is Aibrary, signing off.