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Is this pelvis male or female?
March 29, 2009Posted by on
I’ve noticed that many visitors arrive at my humble little blog by searching for the terms “dimorphism human pelvis” or “pelvic inlet male” or “female pelvis shape.” Up until now, these people have left here emptyhanded- a real shame, since the pelvis is one of my favorite bones. But no more! I bring you Zinjanthropus’s Quick and Dirty Guide to Sexing a Pelvis!
First, you’ll need to find a pelvis, which we’ll define here as two innominates (a left and a right) plus a sacrum. Any old pelvis will do, but it should be from a human, and it should certainly be legally obtained. Once you’ve got a pelvis, you’ll want to get an overall feeling of the shape of the thing. Is it tall and narrow? Short and broad? Men will usually have a taller pelvis, while women will have a shorter one. Look at the iliac blades. Do they form a bowl, or do they flare out to the sides a little bit? A female pelvis will be more bowl-like. The pelvic inlet in a female will be larger than in a male in relation to overall size of the pelvis, and the Sacrum will be wider and shorter as well.
Take a peek at the sciatic notch. A good way to gauge the size of the notch is to stick your fingers in and see how many will fit (Taking into account that everyone has different hand size!). I can usually fit one of my short, stout little thumbs into a male’s sciatic notch, but I can usually get at least my first and second fingers into a female’s. A wider sciatic notch is consistent with females having wider, bowl-shaped pelves. Flexion of this notch coincides with a basin-shaped pelvis.
Next, let’s take a look at the pubic area. In females, this region is longer/wider than in males. In relation to fossil hominids, it looks like this is the part of the pelvis that has expanded to allow for the birth of bigger-headed babies, so it makes sense that this would be larger in females than in males. Look at the area under the pubic symphesis, called the subpubic angle. In males, this angle will be more acute than in females, where it will be fairly obtuse. Again, this is to lengthen the pubic region and make room for baby.
Next, it’s time to look at some details. We can use Phenice’s method to look at the shape of the pubic area. Look at the bar of bone extending from the pubic symphesis. This bar is called the ischiopubic ramus because it connects the ischium with the pubis. In males, it is relatively uniform in thickness and shape as it extends down. In females, it is very narrow right underneath the symphesis and thickens out toward the bottom. Phenice termed this quality a “subpubic concavity,” and it is one of the most accurate ways to sex a pelvis. Where the ramus is thinnest in females, it is also quite sharp on the medial aspect, whereas it is more rounded in males.
Sexing a pelvis is one of those things that takes practice. In fact, that’s one of the problems with it. There are very few things in a pelvis where you can just look at it and say, “that’s a male” without having a good deal of experience. You may think a sciatic notch looks particularly narrow until you see some guy with a REALLY narrow sciatic notch, and then you think, “hmmm, maybe that other one was a female…” Or, you might take the “rule of thumb” from above too much to heart and sex everything as “female” because your fingers are more gracile than mine! The pelvis is one of the most reliable bones to look at to determine sex, but it certainly isn’t foolproof. These are some of the tools I use, but they must all be used together before you can decide that a pelvis is “consistent with” the designation of male or female.
Perhaps the best advice I can offer is that if you don’t already have it, you need The Human Bone Manual, the best field manual on the market. Happy Sexing!