In an interview, Erica Komisar discusses parenting extensively. I appreciate anyone who thinks deeply about parenting, so I mostly value Erica's contributions. However, I believe she is mistaken on many points.

One claim she makes follows a broader pattern that I find troubling. To paraphrase:

"Fathers can take on the primary caregiver role, but they would be fighting biology. It goes against what all mammals do."

I see this kind of reasoning frequently-arguments that begin with "From an evolutionary standpoint..." or "For mammals..." But this argument is nonsense. Not only is it incorrect, but I suspect that most people, when pressed, would find it indefensible. It often functions as a stand-in for more rigorous reasoning.

Disclaimer: Erica makes more nuanced claims to support her perspective. Here, I am only critiquing one specific piece of "evidence"-her appeal to mammalian behavior. She referenced it multiple times (three by my count). I am not attempting to refute her entire viewpoint, only this particular claim.

"It's What Mammals Do"

If we strip this argument down to its core, it amounts to: Other mammals do this, therefore it is natural and acceptable.

I've seen this line of reasoning used to justify claims such as:

Males are more aggressive in most animals; therefore, male humans should be expected to be more aggressive.
Males are more promiscuous than females in most mammals; therefore, promiscuity is natural for human males.
Females are the natural caregivers in most mammals; therefore, human mothers should primarily raise children.
Hierarchies exist in many animal groups; therefore, human social hierarchies and inequality are natural and acceptable.
Alpha males dominate in many mammal groups; therefore, dominant, assertive men should naturally be leaders.
Animals eat meat; therefore, human meat consumption is natural and morally acceptable.

And the list goes on.

1 Prevalence Doesn't Imply Moral "Rightness"

The classic parental retort comes to mind: "If all your friends jumped off a cliff, would you?" Even if we accept these comparisons between humans and mammals, that does not make them morally right.

For instance, all animals experience suffering to some extent. Does that mean suffering is good? Absolutely not. Even if every mammal shares a common trait, that does not prove it is desirable or something we should strive for.

Some examples to illustrate the absurdity of this logic:

Mammals live outdoors; therefore, homelessness is good.
Animals are illiterate; therefore, illiteracy is good.

Clearly, just because something is common among mammals does not mean it is an ideal we should pursue.

2 There Are More Differences Than Similarities

This reminds me of the concept of referential tennis that rationalists discuss. One person might argue, "Most mammals are territorial, therefore humans should be," while another rebuts, "Ah, but among highly intelligent animals, most are not territorial." A third might respond, "Wouldn't you agree that we are most socially similar to prairie dogs, who are territorial?"

The joke here is that comparisons between humans and other animals often involve more dissimilarities than similarities. If your Bayesian baseline is 50/50 (i.e., you have no prior knowledge), then choosing analogous groups can help you update your beliefs-but only to the extent that the similarities are meaningful.

Given this, comparing humans to any other animal ignores millions of years of evolutionary divergence. A rational approach would be to update our beliefs only marginally-if at all-based on such comparisons.

3 Prevalence Doesn't Mean Inevitability

This is perhaps the strongest counterargument. If a trait is present in nearly all mammals, then there must be an evolutionary advantage to it. The argument that follows is: Because this trait is strongly selected for, resisting it is futile.

One flaw in this reasoning is that mammals are not a randomly selected sample. They share many traits simply due to common ancestry, not necessarily because those traits are beneficial.

Another flaw is that correlation does not imply causation. For instance, all mammals have lungs. This might suggest that lungs confer a strong survival advantage. However, gills also work-the reason mammals have lungs is largely due to their evolutionary history, not necessarily because lungs are universally superior.

Some examples to illustrate this point:

No mammals wear glasses; therefore, there must be a strong incentive against wearing glasses.
All mammals have backbones; therefore, having a backbone must be highly advantageous. (But what about successful invertebrates like octopuses?)
No mammals have green skin; therefore, being green must be a disadvantage. (Yet many reptiles and amphibians are green and thrive.)
All mammals have hair at some point in their life; therefore, hair must be essential for survival. (Yet some mammals, like whales, have almost none.)

Correlation can, with additional data, suggest causation-but merely pointing to a pattern among mammals is insufficient. I have never heard anyone say something like:

"Animals don't practice monogamy universally, so humans shouldn't either. Now, if you look at Figure 2, you'll see my causal diagrams where I explore the relationship between evolutionary tendencies and preferred behaviors..."

No one actually defends the "all animals do this" argument in depth. People simply state it and expect it to be self-evident. But arguments that seem self-explanatory often deserve the most scrutiny.

Conclusion

I don't think this argument holds any weight. Often, when people say, "It's not what mammals do," what they actually mean is, "This doesn't feel natural to me." But since "It doesn't feel natural" is not a persuasive argument, they dress it up in scientific language.

This works because it signals to like-minded people: "This is unnatural," in a way that sounds more authoritative.

But that does not make it true.

Full Transcript Quote

This is an excerpt from the YouTube video. You can skip this if you like:

"I'm going to say when men stay home to nurture their children-now remember, as mammals, we have defined roles. It is not instinctual for men to stay home and nurture their young. It's a reversal of something, and the issue there is that there's an inverse relationship between oxytocin and testosterone. The higher the oxytocin, the lower the testosterone. Yes, so if we're staying at home bonding, there are reasons for that. Mammals, when they are nurturing their young, they don't want somebody mating with them-go away, right? So the idea is that when a female nurtures, she doesn't want to..."

[...]

"So there's a whole debate in society about this idea of gender neutrality-that mothers and fathers are interchangeable. But actually, from an evolutionary perspective, as mammals, they're not interchangeable. They serve different functions, and those roles and behaviors are connected to nurturing hormones. So mothers are really important for what we call sensitive, empathic nurturing. When children are infants and toddlers, that means that when children are in distress, mothers soothe babies and therefore regulate their emotions from moment to moment. Every time a mother soothes a baby with skin-to-skin contact, eye contact, and the soothing tone of her voice, she..."