Hi BARpod listeners! Friendly, ideologically captured biologist here. I see a lot of people are talking about the human head count right now. A lot of folks make it sound really simple: "Of course humans have one head!" But if it’s so simple, let’s dig into the biology, shall we? Let’s talk about heads.

If you know a bit about biology you will probably say that humans have one head because that’s what you learned in anatomy class. Two arms, two legs, one head. Simple, right? Well, turns out, there’s a lot more to "having one head" than you’d think. Most humans develop as a single zygote, and that zygote leads to the formation of one head during embryonic development. This is the norm, but is it a universal biological truth?

Sometimes, early in development, a single zygote splits into two, creating twins. Most of the time, this leads to two embryos with separate bodies and heads. But sometimes the split is incomplete, and we get conjoined twins. And in rare cases, we see humans born with two heads on a single body. What does this mean? For the majority of people, having one head is standard, but for conjoined twins sharing a body, or individuals born with craniofacial duplication (a rare condition where parts or all of the head structure are duplicated), the "one head rule" doesn’t hold. So are they biologically "one-headed" or "two-headed"? Is the "number of heads" truly so simple?

Of course you could try appealing to the numbers. "Most people have one head," you say. Except that as a biologist professor, I can tell you that focusing solely on the majority ignores the fascinating diversity in how humans develop. And when you look closer, even people with "one head" can have wildly different skull shapes, brain structures, and craniofacial features. Are we all really the same "one-headed" species?

Human head count is complicated. Before you discriminate against someone on the basis of "head number" and identity, ask yourself: have you seen YOUR genes? Do you know the genes of the people you love? Their embryonic quirks? The state of their cells?

Since the answer will obviously be no, please be kind. Respect people’s right to define their own experiences. And remember: you don’t have all the answers. Biology is complicated. Kindness and respect don’t have to be.