The TRP sidebar includes a link to Briffault’s Law, which is this: “The female, not the male, determines all the conditions of the animal family. Where the female can derive no benefit from association with the male, no such association takes place.” The corollaries aren’t relevant to showing it to be false.

My position is that the actual conditions of association and the animal family are determined by the male or the female based on cost vs benefit calculations. This is true not just for male-female associations but for all associations between animals regardless of sex, age, relatedness, or even species. If either party stops getting a net fitness benefit from the association, then the association will end or coercion will be needed to continue it. This applies to humans too and I think TRP's application of this law is bad in and of itself but that's maybe for another post.

I’ll argue this by outlining two relevant principles governing behavior, explain how each contradicts Briffault’s Law, and provide examples in other great apes.

The first principle: Every individual has a finite resource budget. For most animals, these resources are time, energy, and health. Individuals generally divide their resources between these things:

  1. Growth, development, and maintenance
  2. Food consumption (finding it, obtaining it, processing it, and digesting it)
  3. Resting
  4. Mating (finding mates, competing for them, and copulating)
  5. Raising offspring
  6. Socializing
  7. Avoiding predators

Investing resources in one of these means that resource can’t be invested in another resource simultaneously: if you’re sleeping, you can’t be watching for predators at the same time. Every decision is a tradeoff designed to get the best fitness return on investment. A successful strategy is to balance investments so that none of these things suffer a deficit sufficient to decrease fitness. An unsuccessful strategy is to balance investments in a way that one or more of these things is at a deficit sufficient to decrease fitness.

This contradicts Briffault’s Law because Briffault’s Law requires that males choose the unsuccessful strategy. If a female is the only one determining the length of a male-female association, then the male is not making choices about where to invest his resources based on what would result in the greatest benefit to his fitness. Unsuccessful strategies do not persist into the next generation as often as successful strategies, so they disappear.

Example 1: Gorillas live in troops of one dominant male (usually) and adult females with their offspring. When different troops encounter each other, females will sometimes try to transfer to another group. This is a benefit to her and a cost to her current dominant male.

If Briffault’s Law held true, dominant males would passively allow females to transfer.

In reality, her current dominant male will try to prevent her transfer with violence or threats of violence. If he successfully interrupts the transfer, which is common, the association continues at a cost to her and a benefit to him. Briffault’s Law is shown to be false.

Example 2: Chimpanzees live in multimale-multifemale groups and both sexes are promiscuous. Females exhibit highly visible swellings when they are fertile. Sometimes females will approach males and present to them; sometimes females stay where they are and allow males to mate with them; sometimes females will actively try to escape mating by fleeing, hiding, or exhibiting fear responses.

Briffault’s Law dictates that a female’s preference regarding an association will be respected.

In reality, male chimpanzees routinely attack females who refuse mating. This may continue until the female submits to mating. In other instances, a female may be receptive to mating with a certain male, but a more dominant male has monopolized the female and intimidates or attacks any other male who approaches. In still other instances, albeit uncommon ones, males will ignore a female when she presents to him. This is most likely if the female has a swelling but is too young to conceive but once I saw it happen to a mature female when a male was just too tired-- interestingly, she used violence to get him to submit. In all situations, associations have been initiated or prevented in opposition to the female’s preference. Briffault’s Law is shown to be false.

The second principle: Reproductive success requires two things: making babies (mating) and raising them to adulthood (parenting.) Individuals must choose how to spend their resources between mating and parenting so they get the most offspring surviving to adulthood. The decision on how to spend these resources is influenced by many factors including physiology, group composition, and species distribution. There’s a lot of variation in how primate species invest, and for every identifiable trend there are numerous exceptions. Some general trends are: paternal care is more common when species tend towards monogamy and a male can have some degree of certainty that an infant is his; paternal care is more common in species where distribution is such that, should a male leave after mating, he’s relatively unlikely to find mating opportunities so he might as well invest in parenting; and that paternal care is more common in species where the infant derives a huge survival benefit from it.

Regardless of exceptions, it holds that just like with general survival, individuals must find a balance that works with the specific conditions of their species if they want to be successful. This contradicts Briffault’s Law because Briffault’s Law again posits that males choose an unsuccessful strategy. If the female is the only one dictating association, she will make choices that benefit her reproductive success. In some conditions, this will be at the expense of the male’s reproductive success. If he allows that, he’s not investing his resources in a way the will maximize the number of mature offspring he produces over the course of his life.

Example 1: Chimpanzees live in multimale-multifemale groups and both sexes are promiscuous. This means that sexually receptive females are relatively common and the paternity of any infant is uncertain. When a female is sexually receptive, males tend to group up and follow her for days until she’s no longer receptive. Male-male competition for mating opportunities is fierce.

Briffault’s Law would dictate that once a female stops being sexually receptive, one or more of the males (maybe those who mated with her the most) stay with her and provision her with protection and the extra high-quality food she will need to have a healthy pregnancy. One or more of the males would help care for the resulting infant, sharing the huge cost of parenting an altricial infant with a long period of dependency.

In reality, when the female is no longer sexually receptive, these congregations of males dissolve. When the female has a baby, she will bear the majority of the parental care cost. Due to group composition and paternal uncertainty, male chimpanzees are likely to produce more offspring over a given time period if they try to mate with as many females as possible instead of staying to care for the offspring of one female, even if the baby is definitely his. Males end their association with a female once she is no longer sexually receptive in order to maximize their own fitness, regardless of what would benefit hers. Briffault’s Law is shown to be false.

(I originally planned to include other principles such as altruism/Hamilton’s rule and individual selection vs group selection. Even though they weren’t completely irrelevant, they felt redundant. Even the principles I did include are significantly overlapped, with mating vs parenting effort just being an example of a tradeoff necessitated by resource budgets.)

In short, Briffault's Law contradicts basic principles of resource allocation and cost vs benefit. Males and females both determine conditions of the animal family. Any animal, male or female, who doesn’t regulate their associations based on cost vs benefit is poorly suited to survival.