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Estimating sex from skeletal remains

Estimating sex is critical for making accurate identifications. Dr Rebecca Gowland describes several techniques to assess sex from skeletal remain
Once you have your skeleton in the lab and you’ve laid it out in anatomical position, and you’ve recorded all the bones that are present, the first aspect of identity that you want to establish is sex. One of the reasons that you do this first is because some of the other techniques are sex dependent, and we only sex the skeletal remains of adult individuals. This is because establishing sex of non-adults has been shown to be unreliable. There are a number of techniques that have been developed, but when they’ve been applied to different populations their reliability is not so strong.
Part of the reason for this is that sexual diamorphism, so the differences between males and females, does vary slightly between different populations. So this can be confusing if you’re dealing with juvenile remains. So today, we’re just going to focus on establishing the sex of adult skeletons. The pelvis is the most accurate part of the skeleton for sex determination. And there are a number of morphological differences between males and females. Here we have a male pelvis. The differences between male and female pelves are the most accurate way of determining sex in individuals. You will see that the male pelvis overall is much narrower and steeper, whereas the female pelvis is much shallower and broader.
If we look at this angle here, beneath the pubic bone, we’ll see it’s much narrower in males than it is in females. There are a number of other individual features. And I’ll go through each of these in turn with you. For comparison, here we have a female pelvis. And as you can see, it’s much shallower and broader, the subpubic angle is much wider, and the length of the pubis is much longer. And this is to increase the size of the pelvic inlet and pelvic outlet to facilitate childbirth. The first feature that I want to show you is the sciatic notch. And you’ll see here on this female pelvis that it’s very wide and V-shaped.
If we take a look at the male pelvis, you’ll see that it’s deeper, narrower and more U-shaped. I’ve included here an intermediate example. This one I’ve included because it’s important to remember that these features exist on a sliding scale, from very feminine, to intermediate, to very masculine. If you do have an intermediate sciatic notch, and you’re not sure whether it’s male or female, it’s useful to use the composite arc. Here, you follow the edge of the sciatic notch around the superior surface of the auricular surface. In males, you’ll see that it forms a continuous arch.
When you try to do this in females, you’ll see that it misses the superior surface of the auricular surface, and it forms almost two separate arches. This is another female pelvis and the feature that I want to show you is called the pre-auricular sulcus, that’s this concavity underneath the auricular surface. This feature isn’t present in all females, but when it is, it tends to be quite sharp and quite deep. On males, you rarely see it, but if you do see it, it tends only to be a very shallow concavity. Here are fragments of a female pubis and a male pubis. On the female, you can see that the subpubic angle is quite wide and U-shaped.
On the male you can see that it’s quite narrow and V-shaped. On the female you can see that the angle extends backwards from the pubic symphysis, whereas on the male it just extends downwards. Another feature to look at is called the ventral arc. On females, this is this flattened triangular area here on the anterior or front surface. On males, this is not present. So overall, the female pelvis is much more gracile than the male in terms of the individual features, they tend to be much sharper. Another feature to look at is the length of what’s called the ilio-pubic ramus.
You’ll see that it’s much longer, if we were comparing it to the diameter of the acetabulum- the hip socket here, this is much longer. If we look at the male pelvis, it’s much shorter and is approximately equal to the diameter of the hip socket. Overall, these elongated features of the female are about creating a larger space to help with childbirth. The skull is also very useful for determining sex in skeletal remains. Overall, the male skull tends to be more robust and larger than the female skull, whose features tend to be a bit more gracile. I’ll go through a number of the individual features of the skull with you that are useful in terms of determining sex.
So here we have a male skull and you’ll notice that the eye sockets are much squarer than the female. On the female, they tend to be more rounded and irregular. The rims of the orbit as well on the males tends to be thicker and blunter, whereas on the females, you can see that they’re actually quite sharp. Another key feature is known as the supraorbital ridge or the brow ridge. As you can see, it’s much more defined on the male and here on the female, it’s quite smooth. The center of this ridge is referred to as the glabella, and you can see that this is quite pronounced here.
Whereas on the female, it tends to be much less pronounced and as you can see on this female, it’s completely absent. Here we have a male and a female skull viewed from the side. Now you can see that the female skull is much smaller than the male. One feature you can also see is that the forehead of this female tends to be a little bit more upright, whereas the forehead of the male tends to slope slightly further backwards. When we look at the mastoid process, which is this feature here, you can see that the female mastoid process is much smaller than the male.
The other feature that you can see is this ridge here above the mastoid process in the male, which is quite pronounced. This is the posterior zygomatic arch. If we look at the female, you can see that it’s smooth above the mastoid process and there’s no pronounced ridge. These are the same skulls viewed from behind. As you can see on this male skull, we’ve got a very pronounced region here. This is called the nuchal crest. When we look at the female, you can see that it’s very smooth here. These features are related to musculature; they’re essentially muscle attachment points. As a result of this, you do get a great deal of variety within and between different populations.
So much like the pelvis, the features that we’re looking at form on a sliding scale from very masculine to very feminine. And these differences will vary between different populations as well. As a consequence, sex determination in the skull tends to be less accurate than it is for the pelvis because it is influenced by factors such as lifestyle-so diet, activities, and that interaction with genetics, whereas sexual dimorphism in the pelvis relates to functional morphology linked to childbirth. Here we have two femora and it’s tempting to think that the larger one is going to be male, and the smaller one is going to be female. In this instance, that is the case but it’s not always.
We do have large females and small males, and there is a lot of overlap between males and females within a population. When we’re measuring the femora, we can look at the length, and we can look at the diameter of the femoral head, and we can look at the width of the condyles. And we can look to see whether these fall into a female or a male category. But again, you must be conscious of the fact that there is a lot of overlap between males and females. And I would be very cautious about assigning sex on the basis of size alone. So we’ve gone through the different features for establishing sex from the skeleton.
One of the things that I think is really important to remember is that sexual dimorphsim does vary slightly between different populations. So you will have to accommodate this difference when you’re looking at your own skeletal assemblage. The other thing to remember is that sexual dimorphism is on a sliding scale from ‘very feminine’, ‘feminine’, ‘intermediate’, ‘probable male’, ‘male’. Skeletons don’t just fall neatly into two discrete categories. So again, if you remember this when you’re establishing sex in your skeletal assemblage. In the next section, we’re going to focus on estimating the age-at-death of infant and juvenile skeletal remains and the variety of techniques that we can use for estimating age-at-death.

Sex is one of the first biological characteristics estimated from the adult skeleton. This is because some of the methods of estimating other identifying characteristics, such as age-at-death and stature, are sex-dependent. In addition, in the forensic field, knowing the sex of a deceased individual immediately rules out a large proportion of possible identifications. Although a number of macroscopic methods for determining the sex of infant and juvenile skeletal remains have been developed, current standards generally recommend that this is not attempted. This is because the methods have been shown to have a low level of reliability when applied to skeletons from different periods and places. DNA analysis and peptide analysis can be used to determine the sex of children (discussed in Week 5).

Sex is determined through an examination of the sexually dimorphic features of skeletal size and shape. Differences between male and female skeletons arise from the interplay between genetics, hormonal variation, culture and environment. For individuals who have completed skeletal maturity, sex determination of skeletal remains is considered to be reliable. It is important to note, however, that skeletal features are not polarised in terms of sexual dimorphism – the skeletons can’t always be placed into two neat categories. Instead, the traits relevant for sex determination exist on a spectrum from very feminine to intermediate to very masculine. As a consequence, five categories of sex determination are generally used in anthropological analysis as follows:

  • Female
  • Probable Female
  • Intermediate
  • Probable Male
  • Male

The range of sexual dimorphism expressed may vary between skeletal samples. For example, skeletal samples from different time periods or geographical locations can vary in the extent to which particular ‘masculine’ and ‘feminine’ traits are expressed. These differences arise due to the interaction between social, environmental and genetic factors.

The American Academy of Forensic Sciences has produced an Approved American National Standard for sex estimation in forensic anthropology.

After watching this video, continue on to the following steps, which describe methods for estimating sex from the pelvis (os coxae) and the skull in further detail.

A note on transgender, transsexual and intersex

Last time the course ran we had a lot of questions regarding transgender, transsexual and intersex individuals. This course has cited and discussed methods that enforce the assumed biological sex binary (male and female). Please note that biological sex is complicated and is not as clear cut as what has been previously described as ‘male’ and ‘female’. The forensic community has started to adapt and there is a need to review methods to be more inclusive and representative of the population. This is an ongoing process and may take years to redefine what is seen as biological sex and the research behind estimating biological sex in forensics.

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