Hi Jackster, great question. Actually, it’s more like two questions, so i’ll take them in order.
1) You can determine the sex of a skeleton most accurately from its pelvis and its skull. The pelvisis the group of bones that it most different between men and women (sexually dimorphic) as the female’s pelvis has to allow childbirth, but a male’s pelvis is more streamlined and designed primarily for walking and upright motion. The female pelvis is broader, and has a wider ‘subpubic angle’ – this is the angle between the two sides of hip bone in the front. The opening in the centre of the pelvis is wider than a man’s too, to allow a baby’s head to pass through.
Male skulls are more robust and chunkier than female skulls, which are more gracile and elegant, or finer and more delicate. Behind your ear is a bit mass of bone called the mastoid process – this is much bigger in men than in women. In men too, there are the thick ‘superorbital tori’, or eyebrow ridges, which women don’t have to such an extent. Also , there is a bump at the back of your head in the centre, which is usually much more pronounced in men than in women. We put all these features together to come to the conclusion about whether a skeleton is more likely to be male or female. Because these changes tend to happen as a result of puberty, although it is relatively easy to determine the sex of an adult skeleton, it is not so easy to determine the sex of a child or teenager.
2) We determine age by looking at the development of the skeleton. Babies have lots of very soft bones that gradually fuse together and harden as they grow up. There are blobs of bone at the ends of each of the long bones (arms, legs) which fuse onto the main shaft of the bone at predictable times. For example, the knee joint properly fuses onto the thigh bone at about the age of 15, so if we find a skeleton where it is not fused, we can say that it was younger than 15, and if it is fused, that it is older than 15. Different joints fuse onto bones at different times, so if there are some fused and some not, then we can be more accurate with our estimation. We also use dental eruption, which happens at certain times, to predict age.
Once someone’s skeleton has fully formed, than we look at degenerative changes, such as wearing of the joints of the pelvis and the sacrum. Also, as people get older, we can see things like arthritis in their bones, which indicates older age.
Thanks Anna! I think we all learned a bit of Forensic Anthropology there – we never stop learning from each other and we can’t know about all forensic specialisms – that is why forums like this are so great – Thank you to Jackster for a great question.