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!
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My favorite two methods (from above) for sexing adults is to observe the sciatic notch and the subpubic ramus. I can usually spot the sex even on videos when I’m watching one of those silly Discovery Channel/NGO Channel shows. I keep in mind the sciatic notch of a male will be more like a candy-cane shape where the female will have the “hook” of the cane bent out. The concavity of the female in the subpubic ramus is also hard to miss.
Of course there are those “ambiguous” examples that could go either way…. so the more sexing methods you have (wow, that’s sure to get you some google hits) the better.
Ha! I’ve never thought of it in terms of candy, which is very surprising…
You’ve now convinced me that I should develop a new auricular surface aging method: Phase 1- billowy, like the top of a snickers bar. Phase 2- granular, like the inside of a malted milk ball. Phase 3- Irregular with macroporosity, like a really well-made peanut brittle.
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Can i get more information on d abnormal pelves?
its a female pelvis
Hmmm, from my experience in childbirth all pelvises (is that the plural?) are all male…. By which I mean, designed/evolved with male needs in mind rather than female needs in mind – maybe that’s why they are so hard to tell apart. I mean how crazy to have a pelvis shape that nearly kills many women/babies during childbirth?
I am a newbie to the blogging world, but just written a post on this very subject;
http://pregnancyandchildbirtharoundtheworld.blogspot.com/2011/10/childbirth-are-our-bodies-designed-for.html
Not really understand
There’s also some individual and racial variation in things like the subpubic angle. Female pelvises are classified in 4 major “pure types”, gynecoid (“woman-like”, the textbook example), platypeloid (“flat”, wider and narrower dorsoventrally), anthropoid (“ape-like”, a misnomer, not ape-like in anything besides the outlet contour, very round, wider dorsoventrally than gynecoid, maybe narrower laterally), and android (“man-like”, more triangular). There are all combinations of mixed types as well.
@ pregnancyandchildbirtharoundtheworld — perhaps it’s not so much the case that the human female pelvis is sub-optimally adapted to give birth, but that people often don’t know the best practices. For example, if the woman is laying down horizontally, gravity won’t be of any help and it will be much more harder. It seems that somewhat ironically it’s the European culture with advanced medicine that has the least knowledge on the whole birth subject. There are some articles about that, if I recall one even pointed that the typological and individual variations I’ve mentioned are often overlooked, and they are related with the movements of the baby as he passes through the birth canal. Or something like that. And in some traditional cultures they can actually deal better with these “complications” that turn out to be not complicated at all. It makes sense, one would expect that humankind would be much less fit if giving birth was such a life-threatening occurrence.