We’ve seen that estrogens interact with bones to promote growth and minimize bone resorption, so it would seem that sex steroids do leave a mark on the skeleton. We do see some general sex differences in bones, such as length of long bones and the shape of the pelvis. Estradiol is key for bone growth, but above a certain threshold, it actually stops bone development. Since ovaries produce more estrogen than testes do, especially during puberty, bone growth stops sooner in those with ovaries**.** But, the timing of puberty is variable from person to person. It just takes longer for testes to produce enough estradiol to stop this growth, which affects the height variation seen between/among sexes (Almeida et al., 2017; Dunsworth, 2020). Some skeletal differences are also due to muscle growth influencing bone growth (Dunsworth, 2020).
The parts of the skeleton most commonly used for “sexing” a skeleton are the skull and pelvis. But these bones are very fragile and don’t always survive, so archaeologists may not be able to use these at all. Sexing a skeleton, also known as sex estimation, also doesn’t happen on a binary: archaeologists use a scale of 5 categories, ranging from hyperfeminine to hypermasculine for each bone, and then try to make sense of these variations (Curate, 2022).
Let’s take a closer look at the pelvis:
Is pelvis size actually related to carrying babies? More thorough explorations of hormones and internal genitalia have shown that there might be another explanation: typically female internal genitalia and gonads take up more space than that of males. The pelvis could be larger for the simple reason of holding the ovaries, fallopian tubes, uterus, cervix, vagina, and clitoris, in addition to the bladder and rectum (Dunsworth, 2020).
From an evolutionary perspective, sexual dimorphism has actually decreased over the course of human evolution and humans are the least sexually dimorphic great ape (Larsen, 2003). The difference between the skeleton of a male chimp and that of a female chimps is far greater than it is for humans.
Discovered in 1973 at Teppe Hasanlu in Iran, these skeletons puzzled archaeologists, who dubbed them “lovers” based on the position of their skeletons. While the sex of one skeleton could easily be estimated as male, the second skeleton had many ambiguous traits. Archaeologists ultimately decided this second skeleton was female because of the assumption that the two were lovers. However, genetic analysis found that both skeletons had XY chromosomes - that they were both genetically male. This shows that the relationship between levels of biological sex isn’t always clear-cut and that cultural bias can override biology (Penn Museum, 2017).
[By The University of Pennsylvania Museum of Archaeology and Anthropology - http://www.penn.museum/blog/fun/fun-friday-image-of-the-week/fun-friday-image-of-the-week-the-lovers/, Fair use, https://en.wikipedia.org/w/index.php?curid=44139610]
The Birka viking burial was discovered in 1878 and the individual in the grave was considered to be male from then until 2017. The objects in the grave indicated that this person had been a warrior, which archeologists in 1878 believed could only be true of men. In 2017, genetic analysis showed that the skeleton was in fact female, at least genetically. While this individual’s gender is unknown, we now know the original estimation of sex was incorrect based on cultural assumptions (Hedenstierna‐Jonson et al., 2017).
[By Evalo Hansen - http://fof.se/sites/fof.se/files/styles/full/public/bild/b746bc5a88faa832_org.jpg?itok=NehCwXZq, Public Domain, https://commons.wikimedia.org/w/index.php?curid=62529423 - Sketch of archaeological grave found and labelled "Bj 581" in Birka, Sweden, published 1889]
Almeida, M., Laurent, M. R., Dubois, V., Claessens, F., O’Brien, C. A., Bouillon, R., Vanderschueren, D., & Manolagas, S. C. (2017). Estrogens and Androgens in Skeletal Physiology and Pathophysiology. Physiological Reviews, 97(1), 135–187. https://doi.org/10.1152/physrev.00033.2015
Curate, F. (2022). The Estimation of Sex of Human Skeletal Remains in the Portuguese Identified Collections: History and Prospects. Forensic Sciences, 2(1), Article 1. https://doi.org/10.3390/forensicsci2010021
Dunsworth, H. M. (2020). Expanding the evolutionary explanations for sex differences in the human skeleton. Evolutionary Anthropology: Issues, News, and Reviews, 29(3), 108–116. https://doi.org/10.1002/evan.21834
Hedenstierna‐Jonson, C., Kjellström, A., Zachrisson, T., Krzewińska, M., Sobrado, V., Price, N., Günther, T., Jakobsson, M., Götherström, A., & Storå, J. (2017). A female Viking warrior confirmed by genomics. American Journal of Physical Anthropology, 164(4), 853–860. https://doi.org/10.1002/ajpa.23308
Larsen C. S. (2003). Equality for the sexes in human evolution? Early hominid sexual dimorphism and implications for mating systems and social behavior. Proceedings of the National Academy of Sciences of the United States of America, 100(16), 9103–9104. https://doi.org/10.1073/pnas.1633678100
Penn Museum (Director). (2017, October 17). Expedition—"Hasanlu Lovers". https://www.youtube.com/watch?v=vvhy2Z1BR6Y
