The recent history of evolutionary approaches to human mating and fertility has been one of increasing focus on trade-offs and strategic diversity. I think that lots of people think that evolutionary approaches are mostly about universal human behaviors, but that spectacularly misses the main thrust of the past few decades of research.

The big trend has been in the development and adoption of life-history perspectives, with a special focus on quantity-quality trade-offs. The ideas here involve how reproducing organisms string together sequences of life events (or life histories) that are about maximizing both offspring quantity and offspring quality (i.e., the offspring’s later reproductive prospects). Life-history theory analyzes how time spent mating competes with time spent parenting, how having lots of kids might shorten one’s lifespan, how having more offspring might diminish the quality of each offspring, and related concerns.

With quantity-quality trade-offs come strategic diversity. Both across species and within species, some might shoot for more quantity at the expense of quality, or more quality at the expense of quantity. These days, lots of folks talk broadly about this kind of diversity in terms of fast and slow patterns. As applied to humans, the main idea is that harsher environments encourage faster strategies—emphasizing earlier childbearing and more kids at the expense of investments in quality—while stable, plentiful environments encourage slower strategies.

There have also been real strides in examining sexual and mating variability. Particularly notable advances have come from the conceptual and empirical development of sociosexuality, including the idea of strategic pluralism. This involves the cad/dad dilemma, that is, how women face a trade-off between mating with cads who have good genes or with dads who are good providers. And, again, with trade-offs come strategic diversity. Various features of environments and individuals factor into whether women in a given population, or different women within a population, might lean more toward the good provider or the good genes side of the trade-off.

Notice that strategic pluralism involves not a quantity-quality trade-off, but a quality-quality trade-off. It’s about two different classes of benefits that might help offspring to later become more successful reproductively—the genetic advantages that come from a physically attractive father vs. the material advantages that come from a provisioning father. As to how this relates to quantity trade-offs, some current evolutionary work has become confused. As I explained in a prior post, it is now common to suppose that unrestricted sociosexuality is a component of fast patterns while restricted sociosexuality is a component of slow patterns. In fact, sociosexuality and fast/slow patterns are empirically distinct at the individual level (in the modern U.S., anyway) and probably are more likely to line up restricted/fast vs. unrestricted/slow (rather than the predicted restricted/slow vs. unrestricted/fast) when comparing different human societies.

In my post from a couple of days ago, I discussed this as a 3D rich-sexy-lots trade-off. This is (as though matters aren’t already complicated enough) a quality-quality-quantity trade-off, where attempting to simultaneously maximize both quality aspects (i.e., the Sex and the City pattern) leads to an especially big hit to quantity.

And then I talked yesterday about how serious diversity can arise through goals-and-hints psychological processes. Here, people don’t just inherit specific behavioral patterns or detailed sets of if-then decision rules, but rather have a range of evolved goals and hints and then individually seek to come up with their own behavioral strategies to achieve these goals in the context of whatever local features are relevant.

So don’t expect any easy answers here.

Getting specific

Evolutionary approaches have made advances in sorting through the kinds of developmental regularities, decision rules, and goals-and-hints that drive human behavior generally. There have also been advances in thinking through trade-offs and strategic diversity, and how similar goals being pursued by different individuals in different environments might lead to patterns of divergence across and within populations.

But to analyze a given population at a given time requires a simultaneous focus on the real-world implications of a range of particulars. One needs to focus on how different kinds of individuals in different situations have different realistic solution pathways in achieving a range of at-times-conflicting goals.

With fertility patterns, we have a sense of what some of these particulars are. Is someone’s local circumstance one in which kids often die? One in which kids specifically without fathers often die? One in which kids are useful for things other than one’s own reproduction (e.g., as agrarian laborers)? What’s the local operational sex ratio? What are the mix of features in young local people that lead to mating success? How do local people achieve those features? What are the individual-difference factors that constrain different individuals’ realistic options for pursuing various pathways to social status or mating success?  What are the realistic prospects for stable parenting relationships? How much does relative wealth and social status rely on women’s employment? And so on.

So we might look at modern America, and get specific. Kids don’t often die. They devour dramatically more resources than they produce. Extended formal educations are the primary pathway to enhanced resources and social status, but are costly and seriously delay fertility. Social norms and birth control technology allow for lots of non-reproductive sex, reducing the costs of trying to figure out ways to turn shorter-term relationships into longer-term ones. Divorce is relatively low-cost. Dense populations present lots of mating alternatives. The African American population has a particularly imbalanced operational sex ratio, with substantially fewer living, non-incarcerated young men than young women. High income disparity, declining male incomes, and lower marriage rates imply a greater need for female labor market participation to achieve relative wealth. And so on.

To start understanding modern American patterns, one needs to combine a general sense of the relevant evolutionary goals with lots of the specific factors. Then one can start to map out how differently situated individuals might develop different pathways with different trade-offs in their pursuit of widely shared evolved goals.

This is what I had in mind in my earlier post posing a hypothetical about giving advice to an American teenager who wants lots of rich, sexy offspring. I traced through some thoroughly modern hurdles she would face in terms of education, her own income, and the support of a helpful partner. I ignored individual differences, but these are crucial as well. Is she someone whose family background and cognitive abilities give her an easier path to succeeding in higher education and the professional workforce? Do the young men who are realistically available to her often develop stable, higher-earning patterns that make them useful husbands? To what extent does she have personal features that make her attractive as a long-term partner? What are her available family and community resources that might affect various trade-offs? Within any potentially reproductive relationship, what are the realistic prospects regarding relationship stability and how would (additional) children affect that? What are their sources of income and how would (additional) children affect that? And so on.

There’s just a lot we don’t yet know about how these complicated processes interact. But the current tools give us a sense of the larger patterns. I wrote in an earlier post, for example, about the kind of lifestyle profiles that emerge from combining notions of fast/slow life-history with restricted/unrestricted sociosexuality, such that we can think about fast/restricted patterns, slow/restricted patterns, fast/unrestricted patterns, and slow/unrestricted patterns. This isn’t enough, of course, but it’s something, especially when we notice that the slow/unrestricted pathway seems to be the main driver of low modern American fertility.

I’ve been focusing on modern America in these discussions because my experience is mostly with modern American data. And my conclusion is that we know some interesting things, but in part because the puzzle involves so many complex specifics, we’ve got a way to go. Given the importance of specifics, I’d urge caution in extrapolating into different times and places. For example, the U.S. saw wild ups and downs in fertility just from the 1910s to the 1970s. Explaining 1930s America will require details that make sense of declining overall fertility along with extremely wide individual variance; explaining 1950s America will require details that make sense of fertility rates that rose incredibly quickly and broadly.

Similarly, various other countries require their own explanations. Right now, for example, both Germany and Japan have spectacularly low fertility rates. Figuring out each will require researchers who understand evolutionarily grounded goals-and-hints processes but who also have detailed understandings of social status, mating, and fertility trade-offs that are specific to modern Germany and specific to modern Japan.

Yeah, look, this stuff is hard. It’s slow work that often becomes more difficult the more one knows.