Hello,
Our condition has been around for 30,000+ years, and evolution has kept it till today. There must have been a reason for it!
So, you are telling me that having PCOS might have kept me alive a few thousand years ago?
Yes, scientists think so.
I am breading this down into a history of PMOS mini-series on Instagram.
Exploring this topic has made me feel at peace with my condition. I am at peace with the fact that things don’t happen by chance, and I am grateful that one of my ancestors might have experienced similar symptoms, which allowed her to survive while others did not. I might not have been here today without it.
Let’s deep dive into the evolutionary theories of PMOS.
In this article:
Why do we evolve?
Insulin resistance - why has it helped us
Increased fat storage - how was it an advantage
High testosterone - has it made us survive?
How PCOS looked thousands of years ago
Could PCOS be an advantage nowadays?
Our bodies have evolved according to our environments. As we speak, our bodies are still changing. Some things might be visible from generation to generation, while others will take millions of years. These evolutions respond to the environment to increase survival. The easiest way to understand evolution is the COVID-19 strains. Viruses evolve rapidly, which is why new strains of COVID-19 kept emerging. They become stronger each time to survive.
PCOS is an ancient disorder. We know that because it can be found in every corner of the world, with roughly the same prevalence. It is thought to have originated before the migration of humans out of sub-Saharan Africa 300,000-50,000 years ago. Some suggest that Hippocrates (460 BC-377 BC) might refer to women with PCOS in this passage: “But those women whose menstruation is less than three days or is meagre, are robust, with a healthy complexion and a masculine appearance; yet they are not concerned about bearing children nor do they become pregnant.”
Something to bear in mind before we jump into this explanation is that evolution doesn’t prioritise health or longevity but reproduction. The human body will ensure genes are passed down, not that you live healthily in old age. This might sound a bit mean, but it’s important to note that genes are selfish.
This concept is explored in depth in The Selfish Gene by Richard Dawkins. Genes are selfish entities that have built survival machines, “our bodies”, to ensure they survive. Once we reproduce and pass down genes, we might not be as useful for them.
To understand why PCOS might have been an advantage a few thousand years ago and why our evolution kept it, we must look at what drives PCOS: insulin resistance, increased fat storage and high testosterone.
Insulin resistance
A few hypotheses exist about why insulin resistance has been part of our evolution. Treating this article with a pinch of salt is essential, as we don’t know precisely what happened millions of years ago. However, hypotheses are being developed to help us understand our past and improve our future.
A switch in reproductive needs
This is the ability to switch from having loads of babies and investing little in each to having a few babies and investing more in each. In an environment where resources are plentiful and chances of survival are high, reproduction increases. Imagine giving birth to 10 babies; you would need a lot of resources to be able to survive the process. In an environment where resources are scarce, you’d prefer to focus your energy on giving birth to fewer babies but dedicate more time to their survival. To a certain degree, I see this happening nowadays compared to my great-grandmother, who had 12 children. While food is abundant, many people question if they would have the money to raise 10 children today. Many choose to have one or two children and concentrate their resources on giving them the best shot at a good life. Fun fact: the area of the brain that deals with food also deals with money, so you can think of money as a “food resource”.
Given our evolution, it is advantageous to switch between these two according to the available resources. It is thought that insulin resistance has evolved to enable this switching. This is how:
Helping produce larger babies: gestational insulin resistance is expected to divert more nutrients through the placenta to the baby. Gestational diabetes mothers produce larger babies, hence increasing their survival rate.
Stopping ovulation: Not ovulating means the chance of getting pregnant in environments where survival is hard is lower. This means we will not waste energy on pregnancies that might kill us and the babies. It is important to note that women with PCOS are subfertile, NOT infertile. We might have carried fewer pregnancies to preserve energy and give more attention to those babies to increase their survival. HOW COOL IS THIS?
A re-direction of insulin to the brain
The other way insulin resistance might have helped us survive is through directing more insulin to the brain. Specific organs depend on insulin for glucose uptake, while others don’t. Muscles, liver and fat cells need insulin to take in glucose. Brain, red blood cells and placenta use GLUT3 and GLUT4 receptors to take on glucose.
When people become insulin-resistant, glucose remains in the blood because it struggles to enter muscle cells. As a result, more glucose becomes available for the brain to use.
In addition, specific brain areas depend on insulin to take in glucose: neuronal development (brain cell growth) and cognitive functions like memory and learning. It is thought that more insulin is being redirected to the brain, enhancing cognitive abilities. This is due to the abundance of insulin in the blood when someone becomes insulin-resistant. This suggests that insulin resistance may support a shift towards more brain-centred (cognitive) survival mechanisms favouring social interactions and thinking over physical strategies and strength. To a certain degree, this might be happening in our modern world. Realistically, to survive, you need money. To gather this resource, you need more brain-focused strategies to ensure survival.
This would mean that women with PCOS or people with type 2 diabetes would be smarter. There is no research to suggest so. However, you will notice people discussing insulin resistance, making Alzheimer’s disease worse and contributing to cognitive decline. This is true, but it happens in old age. Remember, evolution doesn’t prioritise longevity but reproduction. If insulin resistance allows you to procreate more successfully, it doesn’t matter if it kills you later in life.
You might wonder why insulin resistance has become an issue nowadays if it’s meant to be beneficial. The answer is in magnitude. Today, a sedentary life and a rich diet have reached unprecedented levels, to which the body gives an exaggerated response, leading to disease.
This is also why PCOS, whilst it might have helped us survive at a certain point in our evolution, is now becoming problematic.
Excess fat storage
Another paper on the evolutionary cause of PCOS takes a different approach and focuses on energy storage. It presents the hypothesis that higher fat storage has helped us preserve energy for times when food was scarce.
Women with PCOS are predisposed to abdominal fat accumulation, including both subcutaneous and visceral fat. Subcutaneous fat acts as a long-term energy reservoir, storing lipids during times of food availability. Visceral fat provides a rapid energy source through lipolysis (breaking down fats into usable energy). This is especially critical during times of physical stress or starvation. Together, these mechanisms ensure that energy is available for survival and reproduction, even in periods of scarcity.
This fat storage would have allowed us to carry pregnancies despite limited resources.
These adaptations might have happened when humans left Africa in the late Pleistocene era and faced colder climates, food scarcity, and fluctuating resources. PCOS-like traits, such as enhanced fat storage, would have been highly beneficial for reproduction and survival.
High testosterone
The last hallmark of PCOS is increased levels of testosterone.
You will be happy to know that Neolithic, Bronze Age, and Iron Age females had notably strong upper bodies closely matching those observed in modern semi-elite female rowers. When we worry that we will become too big if we lift weights, we must remember that the female body was not meant to be of such tiny stature.
Females with PCOS often demonstrate higher muscle mass, physical power, and athletic performance than women without. This is due to our increased testosterone levels. These traits would have provided advantages in tasks requiring physical labour, hunting, or defence, especially in small-scale and ancestral societies. They would also have been an advantage in hard labour.
In addition to strength, higher testosterone levels seem to be associated with certain dominance traits, such as assertiveness, competitive behaviour, and aggression. I don’t know about you, but I have many dominant characteristics. I am known to have a strong personality, so maybe this is where my dominance comes from.
Conclusion
Scientists still don’t know why PCOS existed in ancestral environments. All of the above are hypotheses. We don’t know whether it was adaptive, positive selection, or neutral. What do these mean?
Adaptive means traits that enhance the human’s fitness levels, survival, and reproduction in a particular environment.
Positive selection refers to the evolutionary process where beneficial genetic changes are favoured and increase in frequency over time because they improve an organism’s fitness.
Neutral selection refers to genetic variants that could have spread through randomness in ancestral populations without any significant selective advantage or disadvantage. PCOS is unlikely to be widespread worldwide.
PCOS is best understood as an evolutionary mismatch. Our traits might have been advantageous in specific ancestral environments but become problematic in the current climate, where food is abundant.
Lean women with PCOS, who exhibit higher testosterone without the compounding effects of obesity, may represent the PCOS that existed in ancestral times. In these women, the reproductive costs of PCOS (e.g., subfertility) may have been less pronounced, and the survival benefits of elevated testosterone (e.g., physical strength and resilience) more advantageous.
Lastly, I want to say that PCOS could also be an advantage today if managed correctly. We might carry fewer children, but if we care for ourselves, we can raise strong children, age well, and, if we use our dominance well, have a higher income.
How do you feel about your PCOS?
See you next Sunday,
Francesca
Bushell, A., & Crespi, B. J. (2024a). The evolutionary basis of elevated testosterone in women with polycystic ovary syndrome: an overview of systematic reviews of the evidence. Frontiers in Reproductive Health, 6, 1475132. https://doi.org/10.3389/frph.2024.1475132
Bushell, A., & Crespi, B. J. (2024b). The evolutionary basis of elevated testosterone in women with polycystic ovary syndrome: an overview of systematic reviews of the evidence. Frontiers in Reproductive Health, 6, 1475132. https://doi.org/10.3389/frph.2024.1475132
Charifson, M. A., & Trumble, B. C. (2019). Evolutionary origins of polycystic ovary syndrome: An environmental mismatch disorder. Evolution, Medicine, and Public Health, 2019(1), 50–63. https://doi.org/10.1093/emph/eoz011
Dumesic, D. A., Abbott, D. H., & Chazenbalk, G. D. (2023). An evolutionary model for the ancient origins of polycystic ovary syndrome. Journal of Clinical Medicine, 12(19). https://doi.org/10.3390/jcm12196120
Gluckman, P. D., Low, F. M., Buklijas, T., Hanson, M. A., & Beedle, A. S. (2011). How evolutionary principles improve the understanding of human health and disease: Evolutionary principles and human health. Evolutionary Applications, 4(2), 249–263. https://doi.org/10.1111/j.1752-4571.2010.00164.x
Watve, M. G., & Yajnik, C. S. (2007). Evolutionary origins of insulin resistance: a behavioral switch hypothesis. BMC Evolutionary Biology, 7, 61. https://doi.org/10.1186/1471-2148-7-61
This is sooo good! I have been sharing the evolutionary hypothesis for PMOS with a lot of caveats when women ask me why it happens (and the truth is we don’t know for sure). Such a great thorough explanation of what we do know, thank you!
Looking at conditions through an evolutionary lens can change the conversation from “what is wrong with the body?” to “why might this trait have existed in the first place?” The challenge is balancing that perspective with the reality of modern environments, where traits that once helped survival may interact differently with today’s lifestyle and exposures.