A MULTICELLULAR organism is a spectacular thing. Like all other multicellular beings, we have cells that co-ordinate with each other during growth to diversify into different types. The co-ordination of this process in itself is an extraordinary endeavour: the average adult human is made up of about 30 trillion human cells of around 200 types.

There are several systems by which cells respond to and produce information. Sensory organs can produce triggers, the nervous system acts as an electrically based electrical wiring for superfast connectivity, and individual cells themselves can react to physical forces or to chemicals. These signalling chemicals, most of which circulate in our blood, are known as hormones.

Any circulating chemical that triggers change can be classified as a hormone, meaning they are a diverse group of chemicals. Some trigger organ growth, and those organs then go on to produce other hormones. 

Hormones are also responsible for the ways the body stabilises itself — pressure, temperature, hydration, metabolism and mood — by acting as feedback loops. Scientists have identified more than 50 hormones with known functions in humans, from insulin to adrenaline, but it seems likely there are many more.

Just in July 2024, a “new hormone” was described; named CCN3, it promotes bone growth. During pregnancy it  prevents bones being eroded by the demand for calcium in breastmilk, although it also promotes bone growth outside of pregnancy. 

The system of hormones and hormone-induced change is beautifully evolved. It allows the same “blueprint” which is carried by the genes of all the cells in a person to produce the diversity within tissues of a body. It’s also partly what makes our bodies different from one another. Even in humans with very similar genes, cells respond to their hormonal environment and  differentiate according to the life they experience. 

The key here is adaptability. Rather than operating to a fixed plan, the body is able to build and regulate the parts it needs by using the production of hormones to react. Just as genes themselves adapt over time through evolution, so too do bodies through living — whether that’s in the extreme moments of growth like during pregnancy, or just in the trials of everyday life. 

It’s this adaptability that is handy for the very many animals that change reproductive roles from sperm production to egg production. Hormones also regulate the transition from egg production to gestation in pregnancy; after birth, hormones change the internal environment in human parents, whether they were the one to give birth or not.

In menopause, hormones again act to change the bodies and lives of humans (as well as some whales and chimpanzees, although its occurrence in chimpanzees was only confirmed in 2023). In each of these cases, evolution’s tactic has been adaptation and reactivity. 

Human creativity has followed suit. The discovery and manipulation of hormones is one of the extraordinary feats of the last century. Medical science has discovered that we can actively control the hormones in our bodies. The flexibility gifted to us by our genetic heritage means that with relative ease we can induce changes that are already encoded in us.

The magic of this is easy to overlook. The most celebrated of these interventions is arguably hormonal contraception, most familiar in the form of the contraceptive pill. Hormones regulate fertility — or lack thereof — through the menstrual cycle and differing levels of progesterone and oestrogen in the body.

By controlling the timing of those hormones through taking the pill, women can take the risk of pregnancy into their own hands. Around one in four women between 16 and 49 in Britain use hormonal contraception. Hormones can also be used in the other direction, to promote fertility by stimulating the production of eggs, which is often done to allow for in vitro fertilisation.

Other hormonal interventions are also widespread. Hormone replacement therapy (HRT) is a popular technique to reduce the symptoms of menopause, but HRT can also stimulate breasts into producing milk, allowing parents to breastfeed a baby when they haven’t given birth. Some cancers react to hormones, which can therefore be used to treat them. 

Hormones are often talked about in the context of sex and gender, because the differentiation in sex organs and secondary sexual characteristics are controlled by hormones. However, there aren’t any hormones that are uniquely associated with either XX or XY genetics, there are simply different amounts of the hormones present.

That’s one reason why secondary sexual characteristics, such as the distribution of fat, hair and other body tissues (like the vocal cord mass that produces voice tone), all occur on such a spectrum. Although we all have genetic predispositions to produce a particular range of characteristics, the hormones that we experience before and after birth control the range of their expression. 

Hormones can be used to treat cases where hormones vary from “normal” levels. But that’s the rub — as humans we are all unique and individual. Who decides what is normal is where things can get tricky. Are levels that differ from average ones a medical problem, or simply an example of human variation?

Hormonal treatments are now widely available and like many other substances, their availability doesn’t correspond much with their legality. Another route to getting hormonal treatments, other than being prescribed them by a doctor, is to buy them (illegally) over the internet.

Some effects of hormones are temporary, like the redistribution of fat or a change in the smell and quantity of sweat. Others are more like tattoos: permanent body-modifications like the growth of breast tissue, or the deepening of the voice caused by increased vocal cord mass. However, given that society largely accepts other ways that people choose to modify their bodies and lives — people may dislike unusual diets or tattoos, but very few people argue they should be illegal — it is hard to argue that hormonal treatments represent a special case. 

Hormonal treatments are complicated. Heralded by some feminists as the most revolutionary invention of the 20th century, the pill also causes significant side effects. Many women who use it do so with concern about how it affects the rest of their body, their moods, and their relationships.

It’s often pointed out that a male contraceptive pill is possible in principle, but recent trials have been stopped when men have reported similar side effects. We still don’t know a lot about how the body reacts to hormones and should certainly try to understand, in that case, what the side effects really are.

Nevertheless, the widespread manipulation of our bodies seems to have been for many people genuinely liberatory. It seems that, more widely, hormonal treatment is here to stay. It could be extended to increase the wellbeing of those who want it, as long as we are able to adapt its use to improving the quality of people’s lives.

It’s the very flexibility inherent in the hormonal system that should make us aware of our approach to hormone use. Humans aren’t fixed creatures: we  have the capacity to react to new medicine and discovery with liberatory and revolutionary growth, rather than having to stick to traditions, protocols or preconceived ideas.