Understanding the Trivers Willard Hypothesis Part 2

First part of this essay is available by clicking HERE!

Updated 10-11-22

To recap, the Trivers Willard Hypothesis is the idea that for all animals, especially humans, there are a lot of good evolutionary reasons to be able to vary the gender of their offspring in response to environmental pressures.

atomic, this may be all well and good, maybe it even makes some sense, but doesn’t PROVE that swaying works before conception. Couldn’t people just conceive a gender from luck and then be more likely to miscarry a baby boy or a baby boy? Couldn’t variations in gender ratio boil down to post-conception losses and worrying about what happens before we conceive is nothing but nonsense?

First of all, the fact is that swaying happens without our doing a single thing. Many studies indicate 140-160 boys are conceived for every 100 girls and then so many more boys are lost along the way that the gender ratio falls to 102-106/100 by birth. Even that gender ratio is seriously skewed. Men make 50-50 X and Y sperm and that the gender ratio is any different than that, proves that something is swaying gender blue prior to conception anyway. I believe the best evidence at our disposal indicates that more boys than girls are conceived and then lost.

A couple of new studies claimed to find that more GIRLS are lost and unfortunately this is being reported in the media as “girls are the weaker sex”. BUT if you read these studies (as I have) you’ll find that they were done in people who had done IVF transfers (tells us nothing about natural conceptions) OR who were having recurrent miscarriages (most losses do not fall into this category) AND were later losses – in one case 10 weeks or later, in the other case at 15-18 weeks’ gestation. Most losses occur earlier than that and so no conclusions can be drawn from these studies. I suspect strongly that a preponderance of males are lost via chemical and very early loss and it’s simply that the female babies can hang on a little longer before being lost because they are a bit more resilient than males.

Above all else I do not buy into the idea that babies are conceived and then lost because it makes no biological sense that our bodies would do that – it would be a very poor idea for your genes on an individual level, to conceive a baby, carry it for a few weeks or months, only to lose it to keep the overall gender ratio across the population (which your body, of course, has no way of knowing about) at about 50-50!

Our human eggs are considered “biologically expensive” to produce. Eggs are scarce and precious and every day that passes, we have fewer of them. Compared to sperm, which men are making constantly in huge numbers and can keep on making into their senescence, female humans are born with all the eggs we’ll ever have at birth and our eggs actually start dying off in droves before we’re ever even born. Each day that goes by, we have fewer and fewer eggs. Additionally, during every month of our fertile window, from puberty through menopause, an average of 15-20 eggs in each ovary start to develop and only the best one or two manage to complete the process and are ovulated. So every month, our limited-and-shrinking-by-the-day egg reserve drops by an additional 30-40 eggs. We only have (assuming puberty at 12 and perimenopause at 45) 396 months in which to even conceive, best case scenario, and of course we lose months and years due to pregnancy, breastfeeding, miscarriage, etc. In the grand scheme of things, that’s not a lot of time.

Due to our narrow fertile window, it would be ludicrous for our bodies to waste time conceiving babies with anything less than optimal odds of survival. A woman whose genes allowed her to repeatedly conceive babies with lower odds of survival only to miscarry them, would be needlessly squandering precious eggs and precious months of her limited fertility. Logic dictates that something is most likely swaying before conception simply because the human body doesn’t like waste and is excellent at conservation.

Additionally, miscarriage itself (let alone losses later in pregnancy, such as the 15-18 weeks quoted in one of the studies claiming to prove more girls are lost!) can be a risky business and a woman could end up risking her life for a baby with less than ideal chances of survival – our genes just don’t favor that kind of scenario. Not only would you risk your own life and that of your unborn child, but your already living children – kids without moms don’t always survive very long, even in human societies.

Your genes WANT to survive on an individual level, not because of what is best for the population as a whole. So the genes we have, have been the ones that were the level-best at being handed down through the generations by our primate ancestors and early humans for nearly 100 million years. It is extremely likely that some mechanism(s) have evolved (or been designed into us by God) to make sure that when we get pregnant, if one gender vs. another has better odds of survival, we’re going to be at least somewhat more likely to conceive that gender – otherwise our bodies wouldn’t take the chance. It’s not a perfect system and it may very well be that more boys are lost after conception from lack of nutrients but overall, I believe the data supports the idea that altering the gender ratio prior to conception is a biological fact even tho we do not yet know how it all works.

Ok, then, please explain why, if this Trivers-Willard thingamagigger exists, why don’t poor countries have way more girls and rich countries have way more boys?

This is a complicated and intriguing question that I’ve spent countless hours thinking about. I don’t claim to have all the answers on every aspect of swaying but I have come up with some explanations that make sense to me and seem to fit the facts.

First of all, many countries in Africa DO have more daughters born than is statistically expected, consistently, year in and year out. In fact, most equatorial countries do (with a few exceptions, they tend to be poorer than temperate climates). Also, many countries particularly in Asia and the Middle East, sadly practice female infanticide that skews the gender ratio towards males so much that we really have no way of knowing what the true birth rate is in these countries.

Aside – some of the statistical “data” used to support the French Gender Diet and InGender Diet comes from these countries and should be viewed with a skeptical eye. The FGD book (which the IG Diet is partly based on) quotes very extreme gender ratios from some Asian countries and explains it as due to a high sodium, low calcium diet, but modern research has revealed that the skewed gender ratio in Asian countries is almost certainly because of female infanticide and gender-based abortion.

Secondly, even in poorer countries and times of famine, there are vast differences in the amount of food resources different individuals have access to. Some people ALWAYS have plenty, some people NEVER have enough, regardless of the overall prosperity of the nation in which they live. Aside from financial resources, some people just don’t eat as much as others, or eat much more, due to personal preference, cultural reasons, health or psychological issues. We’ve all heard the expression, “You can never be too rich or too thin” and many times, obesity and overeating is actually affiliated with poverty, not wealth. Over the course of a country’s entire population, it becomes far too complex to tease out these factors. There is no way to really generalize to the individual level, on the basis of the overall GNP of the country in which a person lives.

Third, it may very well be the case that in times of true famine, some women who were in declining condition and might have been more “set” for girls to begin with, decline further and stop conceiving all together (or choose not to conceive due to lack of resources). Women who might have been neutral with equal odds at a boy or a girl, may decline and have more girls. Women who were in great physical condition, may simply not decline in condition enough to have girls and may continue to have sons even if times are harder for them. (One study in Africa found that women who conceived boys during time of famine, had greater muscle mass than those who conceived girls.)

Or, it may be that due to their individual wealth/health, anyone who is able to conceive (or who is WILLING to, because even poor countries and historically, they had/have their ways of preventing pregnancy) may very well be richer and/or in better health than others and may be preselected towards boys to begin with. The couples who might otherwise have conceived girls, may either be unable or unwilling to conceive, skewing the ratio towards the families who were well off enough to remain fertile in the face of famine, and were willing to continue having children even in less than ideal circumstances.

Basically, all this amounts to the levels of boys and girls staying pretty consistent in times of famine – less babies may be born overall because some people who might otherwise have had babies choose not to or cannot have them due to lack of food; despite this, the gender ratio itself would remain somewhere in the ballpark of 50-50.

Fourth, improving/declining maternal condition may be more effective a sway tactic than nutrient deprivation is. (nutrient deprivation is one way of causing declining maternal condition, but there are of course other ways to do the same thing.) Declining condition does not always mean less access to food and more food does not necessarily equal improving condition. People who don’t eat much but eat the right foods, can be in great physical condition while another person can be overly nourished and be in poor condition. The reason why we lose weight to sway pink, is because it’s unreliable and terrible for health to try and gain weight for swaying. Tons of things outside of food resources have been proven to affect the gender ratio – exposure to chemicals, certain diseases, stress, smoking, increasing parental age, excessive exercise; all sway by meeting the prerequisite of declining maternal condition, even in someone who eats 3000 calories a day.

Fifth, humanity has evolved for its entire existence eating very few calories – we can adjust and stay fertile even in a lower calorie environment. The whole idea that women need 2000+ calories a day to survive on, and foods from all four food groups, is new to the human experience. Most of our existence was spent subsisting on a few bites of half-eaten antelope carcass scavenged from some hyenas, a rotten banana, and some termites. We are GOOD at staying fertile and having babies of both genders on not a lot of calories, otherwise there would not be 7 billion of us.

Most women around the world eat a lot less than that and always have, and both boys and girls keep right on being conceived. In fact, it may even be that too much food is causing us to decline in condition/fertility due to health issues so for some of us in wealthier countries, we may actually have too much of a good thing going on and gender ratio may be skewed more pink than it would be otherwise, as a result.

Finally, gender swaying can never be 100% or even close, because if it were, the human race would have died out a long time ago. Nor can it be easy to figure out – it MUST be multifactorial or those clever old wives would have figured it out long, long ago. It’s very likely that there are dozens, if not hundreds of factors with the potential to affect gender ratio, many of which may be utterly out of our control.

Food resources are just one of many cues from the environment that our bodies interpret and use to “decide” which gender has the best shot of survival to reproduce. Luck has to play a part as well – obviously my belief is that you can up your odds with swaying (maybe even quite a lot) but Mother Nature/God has a vested interest in ensuring that there are always both boys and girls being born!!

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