Women Do Not Run Out of Eggs
Are we really born with all the eggs we'll ever have?
This article has been updated with additional research and an overview of the history of our understanding of egg cells.
Please note that the goal of my articles is to explore heretical ideas. This content is not intended as treatment or support for any medical condition.
Content for entertainment purposes only. Not medical or health advice.
Up until the 1950s, ongoing debate was taking place between two contrary schools of thought as to the behaviour of human (and mammalian in general) female eggs.
One school of thought hypothesized that eggs are constantly renewing, with old ones being removed through the process of atresia, and replaced with new eggs made later in life.
The other school of thought believed that a definitive pool of eggs is created during fetal development, constantly running out but never renewing after the fetal period.
For years it was admitted that we don’t really know which narrative is true, and scientists were (as scientists should be) performing experiments and going back and forth between the two hypotheses to figure out which one is true. However, the 1950s brought an emergence of dogma that held the sentiment that human females are born with all the eggs they’ll ever have as a definite truth. Further discourse was shut down. (More on what happened in the 1950s will be covered later in the article).
Part of the reason why it was so easy for the scientific community at large to accept this theory as an ultimate truth, despite ample evidence to the contrary, was due to the ideological sentiment that has been penetrating the scientific community since the 1600s.
From the times of Hippocrates, through the era of Paracelsus, the prevailing medical view of the body was one that saw it as a complex, intelligent system, constantly regenerating and adapting to its environment.
However, the 1600s gave rise to a very mechanistic and reductionist view of living beings, equating living organisms to machines, where all the body’s organs and systems are seen as separate parts that do not interact with each other or the environment. By token of this view, the body is like a car, that gets worn out the more that you use it, moving only in one direction, towards degeneration and obsolescence, from birth onward. I will cover this in more detail in later parts of the article.
In the last 100 years, multiple studies have shown that mammals, such as mice123, naked mole-rats4, prosimians5, macaques6, cows7, rats8, pigs9, and humans101112 all have ovarian stem cells capable of creating new eggs and that the first theory, of eggs being removed via atresia and replaced with new eggs created later in life, is likely the correct one. There is other research supporting this theory, which will be covered in this article. However, due to years of medical academia teaching the dogma that women are born with all the eggs they’ll ever have as stone-cold truth, these findings fail to penetrate the mainstream.
As a preface to the rest of this article, the concept of eggs constantly renewing and new egg creation in adulthood clearly does not mean that women don’t go through menopause.
Even in the fruit fly, an animal known to produce new eggs all throughout adulthood, the rate of oocyte production and egg quality all diminish with age, until the point of total failure to produce eggs, well before the fly dies of advanced age13.
I feel this preface to be necessary, as I’ve received criticism from those who have not read a single sentence of this article but decided to share their thoughts on the basis of my Instagram post alone, arguing that if women were to make new eggs, we would never go through menopause, yet the average menopausal age is nonetheless around 50.
Such reductionist thinking reflects the still-prevalent mechanistic attitude in medicine, with doctors believing that menopause is brought on solely by running out of eggs and that if we can make new eggs that would mean that we wouldn’t go through menopause, apparently forgetting the role that the environment plays in human degeneration, including reproductive ageing.
In reality, menopause is the result of multiple metabolic changes, brought on by a sustained accumulation of biological stressors, leading to the slow deterioration of the uterine environment, and alterations in our production and response to hormones. And as metabolic stress is sustained, it'll lead us to produce lower-quality eggs and eventually cease egg production altogether, just as men produce more defective sperm with age.
Moving away from the mechanistic view of the female body as nothing more than a leaking egg basket can give us better insights into the nature of menopause and the epigenetic factors that lead to poorer egg production with ageing, as well as the factors that cause this menopausal age to fluctuate from as low as 20 to as high as 80 in some women at the very extreme ends of the spectrum.
The two main themes that I want to cover in this article are:
What actually brings on menopause
What actually causes egg quality to decrease with age
Where does the theory that women are born with all the eggs they’ll ever have come from?
In 1951, British zoologist Lord Zuckerman published a report where he provided a careful review of the oocyte numbers of various animal species (rat, mouse, rhesus monkey, rabbit, dog, guinea pig and human)141516 at various ages and noted that the number of oocytes of each species decreased with increasing age.
Preceding Zuckerman’s report were over five decades of scientific debate around whether or not the pool of eggs in female mammals is renewable, however, the publicity around Zuckerman’s report shut down the debate, despite a growing number of studies showing that under favourable biological circumstances, adult mammalian females do produce new eggs. This report led to the basic doctrine of reproductive biology, which argues that during fetal development, female mammals generate a limited stock of oocytes.
“A few studies continued to sporadically surface over the next 10 years that reported experimental findings discordant with Zuckerman’s conclusion, but history shows that the opinion of Zuckerman rapidly became cemented in the field as fact. In turn, studies contrary to this belief were, if one carefully evaluates the literature at the time, largely ignored. […] Using Zuckerman’s reasoning, the dogma of a fixed pool of oocytes being set forth at birth would be invalidated simply by scientific evidence inconsistent with the idea that this population of germ cells [egg cells] is not subject to renewal in postnatal life. As discussed above, such evidence clearly existed, but was still discounted.”17
As mentioned in the introduction, for the last few centuries, mainstream medical ideology has shifted to viewing the body in a very mechanistic way, equating it to a machine, that wears out and decays with time, with little regenerative or adaptive potential. I believe that this ideological climate is the reason why a dogma that views female reproduction as a process of continuous and constant decay was so readily accepted, and why so much resistance is still in place when it comes to accepting the regenerative and creative potential of the body.
When it comes to Zuckerman’s report on a diminishing number of eggs with age, one important aspect seemingly wasn’t adequately considered. Just because the number of eggs decreases with age, this doesn’t mean they’re all the same eggs. Some research is proposing that while the overall number of eggs tends to slowly decline with age, old eggs are constantly removed and replaced with new ones.
We replace our eggs, but when the body’s environment gets too hostile, we stop
Images, such as the one above, have been shared across the internet and in fertility books alike. They mean to show us that before we were conceived, we already existed as an egg within our mother’s ovary when she was still being carried by our grandma. While many people may find comfort in this explanation, feeling a sense of an ancestral bond, there is a great chance that many of us were never carried in our grandmas’ bodies. Many of us may not have even been inside our mom’s bodies very long.
Research in fruit flies, mice and humans has shown that even though we do replace our eggs, just as we replace all the other cells in our bodies on an ongoing basis, once our metabolic milieu gets too unhospitable (more on what causes this later in the article), our production of new eggs dwindles, their quality declines, and eventually, the process of replacing eggs stops altogether. This is why a reality where we simultaneously create new eggs and where our egg reserve goes down can coexist. This is also why Zuckerman’s observations do not disprove the possibility of new egg creation in adulthood. The number of eggs might stay the same, and it can decline. This doesn’t mean that they are the same eggs.
“Our data indicate that the pool of primary follicles in adult human ovaries does not represent a static but a dynamic population of differentiating and regressing structures. Yet, the follicular renewal may cease at a certain age, and this may predetermine the onset of the natural menopause or premature ovarian failure. A lack of follicular renewal in aging ovaries may cause an accumulation of spontaneously arising or environmentally induced genetic alterations of oocytes, and that may be why aging females have a much higher chance of having oocytes with more mutations in persisting primary follicles.”18
While baby girls are born with their ovaries already containing many eggs, we know that by the time they reach puberty, millions of those eggs have been killed and removed by programmed cell death. This is likely a process favouring the healthiest eggs. At the same time, many more of those eggs likely die later in life and are replaced by “fresh” eggs. The reason why our egg reserve doesn’t fluctuate significantly throughout life is because as new eggs are created, old ones are replaced.
In mice, about 60-70 new eggs are produced each day, and for the first three months of life, this makes up entirely for the daily loss of eggs. However, the ratio between eggs lost and eggs produced increases as the mice get older, with egg production eventually dwindling down to zero as the ovarian stem cells stop working1920.
Research done on mice and published in 200421 by Dr. Jonathan Tilly and his team at Harvard University showed that the dogma of a non-renewable pool of eggs doesn’t hold up when it’s considered that up to 33% of immature follicles in the adult mouse are dying off at any given time, which would deplete the ovarian reserve much faster than what normally occurs. The theory of a consistently dying and renewing egg supply in mice was supported by a separate 2006 analysis by Kerr et al22. This was significant as it was previously believed that this is not at all possible in mammals.
Research published by Bukovsky et al. in 2004 shows that this same phenomenon takes place in humans. In young women (ages 18-38), follicles are degenerating and lost in high numbers on an ongoing basis, and replaced with new egg-containing follicles. However, after an average age of 38, this creation of new follicles ceases to happen in the majority of women.
“In adult mammalian ovaries, 60–95% of oocytes are in various stages of degeneration. Block’s quantitative morphological investigations of follicles in women showed wide individual variation, but the numbers in the right and left ovaries were similar, with a tendency to decline with age. However, in the 18–38 yr age range, a relationship between age and the number of primary follicles could not be statistically proven. The number of primary follicles in both ovaries varied between 8100 and 290,000. This lack of significant numerical change during the reproductive period also has been reported in cattle. Gougeon used the data of Block and his own observations and concluded that the depletion of the primary follicle pool is caused mainly by atresia in younger women and by a decrease in the growing pool in older women, with the cross-over point at 38 ± 2.4 yr of age. These observations suggest that in human females new cohorts of primary follicles may replace follicles undergoing atresia until about 38 yr of age, with a lack of follicular replacement after that period causing a significant decrease in the pool of primary follicles.”23