by Sue Black
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The determinant of the first component of our identity, sex, should be very straightforward as we expect it to be bimodal – male or female. The term ‘sex’ is used very specifically in our field and is not to be confused with ‘gender’: the former is used to denote the genetic construction of the individual while the latter relates to personal, social and cultural choices and may be at odds with our biological sex.
The genetic norm for the human genome is the presence of forty-six chromosomes in twenty-three pairs. One of each pair – half of your nuclear genetic composition – is donated by your mother and half by your father. Twenty-two of the pairs, while differing slightly from each other, have the same dual ‘form’ (a bit like pairs of vaguely matching black socks) while the twenty-third, the sex chromosomes, carry sex-related genetic information and are therefore quite distinct from each other (like mismatched socks of different colours).
As most of us will remember from our school biology lessons, the X chromosome contains the blueprint for ‘femaleness’ and the Y chromosome that for ‘maleness’ (specifically in the SRY gene of the chromosome). Females carry an XX combination of sex chromosomes and males an XY combination. So we all inherit an X chromosome from our mother. If the chromosome donated by a father is also an X, the baby will carry an XX combination and develop into a female. When the father provides a Y chromosome, the baby will become a male. There are rare disorders of the sex chromosomes which produce alternatives to the usual pairing, including Klinefelter Syndrome (XXY) or Turner’s Syndrome (XO), but these are so uncommon that I am not aware of ever having come across any of them in my entire career.
The developing embryo has a genetic sex from the moment the sperm fuses with the egg, but for the first few weeks of its development it appears to be asexual, with no obviously male or female external or internal characteristics. Even by eight weeks after fertilisation, there is little sign in the soft tissue of a human embryo to indicate whether it will become male or female, but by twelve weeks we start to see evidence of which sex the fetus may be. When Mum is having her first ultrasound scan, it might be possible to determine the sex of the fetus from the visible external genitalia.
These days, some hospitals choose not to confirm the sex of a baby, ostensibly because of staff shortages and the time required to make the assessment, but they will have other concerns, such as the risk of litigation if they get it wrong and the prevention of selective abortion by couples whose culture values one sex above the other. So the baby’s sex may remain a mystery until the day it is born, as it always was in the days before ultrasound. I rather like the element of surprise and never wanted to know in advance what sex my babies were. As my father-in-law said, ‘What does it matter as long as there is one head, ten fingers and ten toes?’
If the parents are keen to know, and the ultrasound operator is prepared to tell them, what he or she will be looking for on the image is the same visual external evidence used by the nurse, midwife or whoever is present to announce a baby’s sex when it is born – if it has a penis it is a boy, if it hasn’t, it is a girl – which then becomes its legal description. There is much wrong with that as a basis for determining the legal sex of a child, biologically, socially and culturally. But since the dawn of time it is what we have relied on, and it is still the best we have.
From that moment on, the agenda for a baby’s entire childhood is usually set in stone. They will be brought up as either a boy or a girl, with all the cultural trappings that definition brings, purely on the basis of whether or not they have a visible penis. If we got it right, when a boy goes through secondary sexual changes at puberty, he will be expected to develop appropriately sized external genitalia (testes and penis), male pattern hair distribution on his arms, legs, chest, armpits, pubic region and face, and a deepening of the voice. A girl will show breast development, widening of the hips, armpit and pubic hair growth and will begin to menstruate. Imagine the effect on your confidence in your own identity if, for the first twelve years of your life, you have believed yourself to be a boy and then you start to develop breasts, or, having always been told you were a girl, you notice hair appearing on your chest. Puberty is a period of great sensitivity and awkward awareness of our bodies at the best of times, and unanticipated alterations of such magnitude are understandably devastating to a young person.
In the vast majority of cases the designation of sex when we are born is correct but the forensic anthropologist must leave room for other possibilities. It would be handy for us if male skeletons were blue and female skeletons pink. Ridiculous as that sounds, let’s use those colours for a moment to represent the maleness and femaleness of our bodies. Blue stands for the presence of the SRY gene and the production of the sex steroid testosterone, while pink represents its absence, which allows the other sex steroid, oestrogen, to predominate. Every baby has a combination of both sex steroids, just in different proportions. Since male embryos have one X chromosome, in addition to the dominant testosterone they are also producing oestrogen as a normal biochemical function. And females produce small levels of testosterone through anatomical routes that do not involve a Y chromosome, for example the ovaries and adrenal glands. If you are in any doubt, ladies, wait until after menopause, when oestrogen declines, allowing testosterone to assert itself, and watch your beard and moustache grow. The bearded lady beloved of Victorian circuses was not a freak of nature but a perfectly normal human variant.
Sex, or what we perceive to be maleness or femaleness, is largely about the interaction between genetics and biochemistry and the effects this has on all of the tissues of the body, including the brain. Imagine a genetically pink embryo that goes into overproduction of testosterone (as happens when a gene mutation causes adrenal hyperplasia), or a genetically blue embryo that either does not switch on its SRY gene or fails to produce enough testosterone (adrenal hypoplasia), or goes into overproduction of oestrogen, and you start to see how the interplay between genetic sex and physical appearance or psychological identity become conflated.
The forensic anthropologist needs to be aware that the features we see in the skeleton are a complex interaction between the genetic blueprint for sex and the effects of biochemistry, resulting in a grey area (or perhaps, given our colour scheme, that should be a mauve area) where genetically male individuals may display some feminine characteristics, and genetically female individuals appear more masculine, than their counterparts at opposite ends of the scale, where genetic sex and biochemistry are perhaps in closer harmony. What is so wonderful about the human is that we have so very many possible variations. It is what makes us truly fascinating to study as a species.
Even when human remains are relatively recent, determining biological sex can be challenging, especially if there has been some surgical intervention. It is therefore extremely important that we are not influenced by circumstantial evidence (the remnants of female underwear, for example) and that we are alert to the possibility of any congenital features or surgeries. The absence of a uterus may point to the remains being male, or they could be those of a woman who has had a hysterectomy or who was born without a womb due to agenesis (the failure of an organ to develop during embryonic growth). The absence of a penis or signs of breast augmentation may suggest that the deceased was female but equally, they could be indicative of elective transgender surgery.
After the Asian tsunami of 2004, in which a quarter of a million people lost their lives, the issue of biological sex and gender was prominent in the minds of many whose job it was to try to categorise and identify the dead. One of the affected countries, Thailand, is recognised as the transgender capital of the world. With a male-to-female operation here costing almost a quarter of the price charged in the US, over 300 such surgeries are performed in Thailand every year, and the third sex, or kathoeys, are acknowledged as a fully integrated sector of society. A strictly dimorphic approach to gender expression cannot be expected in this part of the world and in the wake of
the disaster, external body assessments were always supported by internal examination.
Assigning biological sex becomes trickier as a body starts to decompose. External genitalia deteriorate quite rapidly after death and examination of internal anatomy through postmortem dissection may be of limited assistance. Using DNA analysis to look for the SRY gene will help to confirm remains as male but it is of little value in verifying that they are female unless a full karyotype (a profile of an individual’s chromosomes) can be established. So what do we do if all we have available to us is some dry, scattered or buried human bones?
In spite of my pie-in-the-sky wish for blue and pink bones, an intact adult skeleton is actually already a reasonably reliable indicator of biological sex. The features we look for are those manifested when growth is accelerated during puberty in response to the effects of increased levels of circulating sex steroid hormones. If the predominant hormone is oestrogen, the changes in the skeleton will reflect what we read as ‘feminisation’ of the bones. It does not necessarily mean the individual is female, simply that it displays ‘pink’ characteristics. Here we expect the major change to relate to preparation of the pelvis to facilitate fetal growth and to permit a baby’s head to pass through it unhindered.
Female pelves do not always comply with the norm, however. Cephalopelvic disproportion was a justified fear for pregnant women in the past. If the pelvis was not sufficiently capacious to allow the baby’s head to enter, pass through and then exit the bony part of the birth canal, they might labour for days with no obvious or survivable solution to the impasse. Remember the fate of the Roman mother and triplets excavated in Baldock. Over the centuries, many have died from the traumas of childbirth.
In circumstances where saving a mother’s life was considered more important than the survival of the baby, some gruesome obstetrical tools used to be employed to try to rescue her from cephalopelvic disproportion. The perforator, for example, was a metal implement shaped like a small lance that would be inserted into the mother’s vagina and pushed beyond the cervix into the uterus, where it would ‘perforate’ the first part of the baby it encountered. As in most normal births this would be the head, the perforator was most frequently used to pierce the anterior fontanelle of the skull, the largest of the ‘soft spots’ that allow the bones to move in relation to each other so that the head can get through the birth canal.
A hook on the end of the perforator would then be moved around to find some bit of the skull it could latch on to, often an orbit (eye socket). In the process, it would disrupt some of the brain structure, making it easier for the baby’s head to be forcibly pulled through the birth canal. Later perforators had a scissor-like action which enabled the baby to be removed literally one piece at a time.
Cephalopelvic disproportion is seen less often nowadays, mainly as a result of improved health but also perhaps as a rather brutal example of the survival of the fittest, whereby feto-maternal mortality has resulted in the phasing out of unsuccessful pelvic shapes. Even today, however, in some parts of the world, giving birth can be a hazardous business for both players who have a skin in the game. The World Health Organisation (WHO) reports an estimated 340,000 maternal deaths, 2.7 million stillbirths and 3.1 million neonatal deaths every year, almost all in impoverished countries. In sub-Saharan Africa, a woman’s risk of dying while giving birth is 1 in 7 and cephalopelvic disproportion still accounts for over 8 per cent of maternal deaths.
Where there is access to adequate medical services, it no longer matters if the pelvis is the wrong shape or size because the baby can be removed by Caesarean section with a very high success rate for both mother and baby. In some more affluent countries, advances in anaesthesia and antibiotics have seen C-sections become almost elective as a result of the ‘too posh to push’ trend. And in situations where the wellbeing of both mum and baby are deemed too much of a financial risk for a hospital to follow the natural route, C-section is sometimes seen as a safer alternative.
So the twenty-first-century Western woman now comes in a range of shapes and sizes, all of which can legitimately be preserved in the genetic inheritance of pelvic shape. Ironically, it seems that determining sex from the pelvic bones may well be achieved with greater accuracy and reliability in archaeological specimens than in recent forensic samples, because the level of sexual dimorphism required to maintain successful childbearing heritage is being lost.
When the dominant circulating hormone is testosterone, its primary purpose during puberty is to increase muscle mass. We are all aware of how ingesting additional amounts of the male hormone in the form of anabolic steroids decreases fat levels and increases muscle bulk in bodybuilders. The bone-muscle equation is a simple one: stronger bones are required to withstand the forces exerted by the attachments of stronger muscles. In areas such as the skull, the long bones and the shoulder and pelvic girdles, we see more well-developed sites of muscle insertion. Testosterone, then, leads to masculinisation of the skeleton, but again, that does not necessarily mean that the remains are biologically or genetically male.
If there is no dominant circulating hormone, as will be the case in pre-pubescent children, the skeleton will tend to retain a paedomorphic or childlike appearance, which is generally interpreted as being more pink than blue. As the relevant changes we look for in the skeleton do not occur until puberty, sex cannot be determined with any degree of reliability from a child’s skeleton.
If the entire adult skeleton is available for analysis, the forensic anthropologist will probably be able to correctly assign biological sex in about 95 per cent of cases, although different ancestral groups will show variations that we must take into account. For example, the Dutch are officially the tallest ‘race’ in the world but their babies are not any bigger than those of other Western populations. Not surprisingly, therefore, they have a very low level of obstetric complication because the proportionately larger Dutch female pelvis has not needed to adapt to ensure the safe passage of the baby. Women from other groups who are smaller in stature but deliver babies of the same size are believed to exhibit greater levels of sexual dimorphism in the pelvis as nature has sought to find a shape that will safely accommodate childbirth. This research tells us that it is potentially more challenging to distinguish between female and male Dutch pelves from skeletal remains.
Obviously, if the skeleton is damaged or disrupted, perhaps by fire or fragmentation, the determination of sex becomes increasingly difficult. To establish sex with some confidence requires us to be able to recognise the smallest fragment of bone and identify its location within the skeleton – is it from the distal humerus, proximal femur or a supraspinous piece of the scapula? – as we search for those independent areas that show the greatest differences between the sexes. So we are reliant on the survival of the most dimorphic areas of the skeleton. The shape of the greater sciatic notch in the pelvis, the prominence of the nuchal muscle markings at the back of the neck, the size of the mastoid process behind the ear and the presence of supra-orbital ridging under the eyebrows all hold important clues.
The greater the degree of sexual dimorphism, the more reliable the forensic anthropologist’s findings will be when establishing sex from the bones. But we must always remember that the features on which we are basing our analysis are indicators of the extent and timing of biochemical influences, not proof in themselves of the biological or genetic sex of the individual.
Determining the sex of an unidentified body correctly is very important, because obviously, when trying to match a body to a missing person, being able to eliminate all members of the opposite sex will halve our pool of possible candidates. But the other side of the coin is the very real danger that, should we get it wrong, the chances of ever making a positive identification will be remote.
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Whereas we are quite successful at establishing the correct biological or genetic sex for an adult but pretty rubbish at it with children, when it comes to the second biological component
of identity – age – it is the other way round. When you consider the trouble we have judging with any precision the age of living adults, who provide us with many more clues than the dead, it should not come as a surprise that determining age from remains is not easy, especially when they are skeletonised or, worse, fragmented.
In life, pinpointing age accurately becomes more difficult the older people become. We could walk into any primary school classroom and form a fairly good idea, to within a year or so, of the age of the children there. With a class of secondary school students, we are likely to get it about right when looking at them as a group, but there will be some individuals who appear either a lot older or a lot younger than the majority because they won’t all be experiencing the various physical changes associated with puberty at the same time. As for guessing the ages of a roomful of adults, well, we all know that if we try that, we may flatter some but are likely to end up offending at least half of them.
In the early years of life there is a strong relationship between age, facial appearance and size. The face is a reliable indicator of age because of the way it needs to grow to accommodate dental development. I took a photograph every year of all of my children on their birthdays, which allowed me to create a chronological map of how and when their faces altered (all good scientists regard their children as their own personal little petri dishes). The first big change occurred in them all between four and five years of age, when the jaws, which form the bottom half of the face, have to grow sufficiently to allow the first permanent molar to erupt into the mouth when they are around six. The second significant change was just before puberty, as their jaws grew again to ensure that there was room for the arrival of their second permanent molars. Then all hell broke loose as the raging sea of hormones crashed into their lives (and ours) during puberty, when their beautiful, grown-up faces began to emerge.