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How do you know if you're a boy or a girl? The answer may be a little more complicated that we think.

Go to to get your very own Want/Will/Won't Poster:

You can ask Lindsey Questions at:

Host: Dr. Lindsey Doe

Directing/Filming/Editing: Nicholas Jenkins

Titles: Michael Aranda

Executive Producer: Hank Green

Music in this episode is by Kevin McLeod:
Lindsey: Take a moment and look at your nails. What if I told you that the way you look at them determines whether or not you're female. Female is like this, male is like this, intersex ...? Hopefully, you'll be curious, hopefully you'll wonder what actually DOES determine whether or not a person's female. It can't possibly be how you look at your nails?


How about the way you check out the bottom of your foot or shoe? How do you take off your shirt? Look up at the sky? Sit on the couch? Try this one: Butt, knees, heels flat against the wall. Keep them like that and then try to pick up a chair. Go ahead! Try it out! Determining whether or not a person is female is a pretty elaborate endeavor which some of us start very, very early, as early as sperm!

One technique involves placing semen in a gel-like obstacle course. The faster male sperm will make it through, whereas the more resilient female sperm will stay behind.
Another microscopic sorting hat is called cytometry. The sperm is stained with fluorescent dye, x glows more, y glows less. With 50 to 80% accuracy, clinicians are able to inseminate an egg with the preferred sex sperm - into the vagina with you! Or the petri dish. A third way to control for sex is to grow embryos outside of the body, then extract cells and take a peek to see their chromosomes.

You've probably been taught that xx is female and xy is male. These are the sex chromosomes. Combinations can be xx and xy but they can also be xxx, xxxx, xxyy, xxy, xo, and so on. There are even mosaics where one cell is one combination and another cell is another combination. Bodies are not binary.

There are theories. Conceived in tropical weather: female. Conceived during the winter: female. Conceived when the parents aren't co-cohabitating: female.  Theories pair male offspring with more frequent sex, higher levels of stress, and deeper penetration. Check out Shettles Method or Whelan's Method if you're curious about the timing of conception. Wow.

During pregnancy, females are associated with more severe morning sickness, faster heart rates, sugar cravings, break-outs, softer hands, smoother movements, and a higher baby bump; whereas males are associated with higher calorie intake, slower heart rates, craving for salts and sours, a glowing complexion, dry hands, clumsiness, and a low bump.

Some will stand by intuition as the determinant of sex. If it feels female, then it is female. Dr. Ramzi Ismail has another solution: If this is the uterus, it is more likely that the offspring will be male if the placenta is on the right side; if it's placed on the left side, female. But this has nothing to do with the placement of the embryo, it has to do with the placement of the placenta.

At week six all embryos look the same; differentiation of any kind doesn't actually occur until week seven, eight, nine, when gonads show up.

Testes would point to male, ovaries to female... if any of this were black and white! Just like chromosomes, heart rates, and intuition, gonads have more than two variations. Like one teste one ovary. Or no gonads at all, or ova-testes, a gonad hybrid with features of ovaries and testes, all of which influence sex hormones.

If the embryo is exposed to a lot of androgen, then the reproductive system likely develops into epididymis, vas deferens, seminal vesicles. If not, the embryo maintains the default system of a female and goes the way of Fallopian tubes, uterus, upper two thirds of the vagina. The heavy load of androgen typically comes from the embryos own testes, but what if there isn't enough to fuel the masculine map? Or what if the female embryo is exposed to extra androgen via the umbilical cord? Diversity.

Sometimes we know this is the case. Other times we find out, but most of the time we have no idea at all because these are all internal structures including the testes, which do not descend into the scrotum until the last weeks of pregnancy, if ever.

At four and a half months, the could-be clitoris is the same size as the could-be penis. This is where ultrasounds and the technicians who oversee them come in.

The not-so-official terms are: hamburger sign and turtle sign. The assumption is these images will become even more differentiated.

So at birth the person delivering will look between babies' legs and quickly judge - penis: male, no penis: female. One in a hundred babies, that's 70 million people, will bust the dichotomy. With their intersex genitals and even more will grow up to question the sex they were assigned.

Sex is not any one of these indicators. Sex is a construct that we exhaust ourselves and our resources trying to discern whether it's games, genetics, theories, traditions. And it may just be that the answers are as diverse as the people we question.

So, am I female? Tell me in the comments below and remember that sex is not gender. We'll get to that in the next episode. A great reason to stay curious.