Why Are More Human Males Conceived?

Something I’ve always found a bit weird is the way nature treats human males. Women tend to have a lower mortality rate at every age.  Beginning in the womb, male fetuses have a higher mortality rate. Depending on the area of the world and the medical care, there’s a male to female conception ratio estimated to be from 107 to 170 males to 100 females. By the time a woman gives birth in the United States, there are only 103 to 106 males to every 100 females born. In other words, most miscarriages are male. This doesn't mean that human females aren’t miscarried; only that more males are miscarried.

Looking at the possible conception rate of males versus the number of miscarriages of males is a disturbing idea. I tried to find out where and why someone would come up with the idea of 170 conceptions of males but the data is rather sketchy. The problem is that each country has its own ideas of how to handle statistics. Thus I’m going to go with a lesser figure of 106 male conceptions to 100 female conceptions. This is the usual figure I’ve seen for the male/female conception ratio in the USA.

However, miscarriages are just the beginning of the human male’s challenging journey through life. The very instant of a sperm entering an ovum there is a visible indication of what the males will face from then on.  Recently I wanted to explain to someone about the way that gender is determined in humans. I pulled up all kinds of photos and drawings of the gender determination chromosomes. That’s when I realized the very first predicament a human male has to survive until he’s born: the pathetic ‘Y’ gene that determines the male gender.

I saw this disparity between the male ‘Y’ chromosome and the female ‘X’ chromosome shortly after DNA was understood in the 1950s. I was not only baffled but believed there was probably a mistake made. The male ‘Y’ chromosome was so small, so insignificant so…! I figured that as more was known about DNA the scientists would find out that the ‘Y’ chromosome was probably as big or almost as big as the female ‘X’ chromosome. Boy was I wrong!

Of course, anyone who has even a rudimentary knowledge of genetics knows about the genetic component of gender. Females have two X chromosomes and males have one X chromosome and one Y chromosome. The X chromosome in both the male and  female are strong, healthy-looking specimens of chromosomal attributes. That poor wretched 'Y’ chromosome looks totally unprepared for life in general, much less life in the body of a strong male willing to rule everything from their home to an entire empire.

Words alone cannot convey the difference between the ‘X’ chromosomes and the ‘Y’ chromosome I found links to show their respective size and healthiness. If you have any doubt about my concept, please check these: http://www.google.com/imgres?q=x+and+y+gene+images&hl=en&sa=X&tbo=d&rlz=1T4ADRA_enUS475US475&biw=1280&bih=737&tbm=isch&tbnid=94fsteZDxmY6FM:&imgrefurl=http://www.gnxp.com/new/2010/08/05/y-chromosome-ii-what-is-its-structure/&docid=wGl2Euu8QGIcpM&imgurl=http://phylogenous.files.wordpress.com/2010/07/physical-picture-of-chromosomes.jpg&w=600&h=514&ei=9jjQUIm4AtDyyAGfzoGYBw&zoom=1&iact=rc&dur=400&sig=111133139968444819813&page=1&tbnh=140&tbnw=220&start=0&ndsp=29&ved=1t:429,r:10,s:0,i:120&tx=140&ty=99


The unusual thing is that the ‘Y’ chromosome is the dominant chromosome. For such a little thing the ‘Y’ chromosome has to overcome 3 of the ‘X’ chromosomes. Okay, not so literally but the idea is that like brown hair dominating over blonde hair, so must that little ‘Y’ chromosome dominate over the ‘X’ chromosome. Obviously size isn’t everything!

With my figure of 106 male conceptions to 100 female conceptions I will envisage that perhaps there will be 11 miscarriages during the pregnancies of the 206 females who are pregnant with those 106 male fetuses and 100 female fetuses. At birth there will still be more boys than girls! During pregnancy those miscarriages were perhaps 6 boys to 4 girls. The gender birth ratio is then 100 boys to 96 girls.

After birth, it really becomes difficult for the little boys to survive. Among the smallest premature babies, females again have a higher survival rate. Even with modern American medicine, little boys will die more often than little girls. By age five, females often outnumber males, 100 girls to only 98 boys. It’s very hard to pinpoint the exact reason for human males have trouble surviving. Of course, these figures can’t be accurately pinpointed. This is partly due to the different means that the statisticians
and demographers use and partly due to factors such as selecting for gender, etc. The latter situation is not a major problem in the USA.

However, the fact is that by the time females are past menopause, they outnumber men.  As I’ve noted, the entire purpose behind DNA, X and Y chromosomes and the length of time a human lives is to make sure the species (not the individual) survives. This concept seems at cross purposes to the battering the human male has to go through from conception onward. Males have an extremely difficult time surviving from the time of conception until old age. I’ve pointed out how the human female outlives the male by approximately 4 years.  I also wrote about the male/female ratio at conception and linked to a couple of pictures that show how vastly different the male ‘Y’ chromosome is to the female ‘X’ chromosome.

It’s important to note that this disparity between male and female birth and survival rates has been noticed since 1662. So this isn’t some new phenomena just coming to experts’ attention. In fact, in 1662 there was no modern medicine to keep women going after their reproductive years. Until the middle of the last century you need only read my autobiographical posts on Monday to realize that childbirth was the primary cause of death in women until the majority of women went to hospitals and were given modern medical care. It wasn’t at all unusual for a man to go through 2 or 3 wives before he even reached middle age. That means that the writings in and after 1662 were noticing that once a woman passed childbearing years she was likely to outlive the men in her life.

However, some demographic researchers feel that there is a positive side to this. They do not consider the higher mortality rate in males to be a problem. Bertrand Desjardins, a researcher in the demography department of the University of Montreal, explains, “Men dying sooner than women make sense biologically: because 105 males are born for every 100 females, it would assure that there are about the same number of men and women at reproductive ages. " http://www.scientificamerican.com/article.cfm?id=why-is-life-expectancy-lo

Another explanation is: Biological factors affecting the sex ratio consistently favor females. Evolutionary theory predicts that the sex ratio should equilibrate at 1:1 as this is the only stable strategy. One would expect from this to see an equal number of male and female births. http://camtriplehelix.com/journal/issue/8/the-race-to-the-egg

There is an added factor involved in this discrepancy between male and female conception and birth. During times of stress the ratio between male and female births usually does become 1.1. The most likely cause is that cortisol is created by the mother’s body during stressful times and male fetuses aren’t as capable of surviving an unusually high amount of cortisol in utero. http://camtriplehelix.com/journal/issue/8/the-race-to-the-egg

There again, it seems to have little impact on the survival of the species. Yet, wouldn’t it make more sense for more males to survive in times of stress because they would be a help in times of crisis? The problem with that theory is that human infants, male and female, have such long childhoods that something that created the stress is usually no longer applicable when the male child is old enough to combat a crisis.

In other articles I’ve seen attempts to use socioeconomic criteria to explain the birth ratio differences. Some of the factors considered were: maternal age, paternal age, and birth order. There were some indications that the younger the mother the more likely her first offspring will be male.  The researchers have also found a minor correlation between the decreases in male births and the higher paternal age. http://www.ncbi.nlm.nih.gov/pubmed/3071849

All of the above are samples of many ideas and explanations I’ve come across in the last few weeks about the male/female ratio in humans.  However, all of these things are merely proximate causes of explaining the generally higher ratio of male conception and lower male survival in utero until old age. Proximate causes are not and cannot be the ultimate explanation of the ratio of living and dying between human males and females throughout their lives.

I have yet to see an explanation of the most important issue about this human male/female ratio: what has the shorter life span of the human male got to do with the survival of the human species?


Filed under: Anthropology


Leave a comment