Male disposability is deeply rooted in both biology as well as social expectations and the social conditioning that results from these expectations.
Biological causes of Male disposability
Humans have evolved as a sexually reproductive species as opposed to asexual reproduction. The chief distinction between Males and Females is on the investment in the zygote: females provide the bulk of the cytoplasm via a large egg and half of the genetic packet, while males contribute only the other half of the genetic packet (via the sperm cell).
At the same time, there are resources consumed to raise a Male which could have otherwise gone to raising a Female. Assuming a sex ratio of 50:50, on average the sexually reproducing species ‘wastes’ 50% of its resources, compared to an asexual species where, all else being equal, asexuality is twice as efficient at converting resources into descendants (The evolution of sex, John Maynard-Smith).
Males cannot contribute to the propagation of species as they cannot bear offspring, which places the limit (bottleneck) to species growth entirely on Females. If all but one male were wiped out, it would not be the end of the species as it only takes one male to impregnate all the females and sire the next generation, thus ensuring the continuation of the species. However, if all but one of the females were wiped out, the species would be poised on the brink of extinction.
Females are the bottleneck to the propagation of the species
Because Females are the bottleneck to species growth, and Males take up resources which could otherwise have gone to raising offspring, and only a few Males are required to sire the next generation, (and only a few do - these are the ones which posses or display the highest selected or fitness traits for the species), nature has made it such that males are inherently disposable. Thus in certain species, a male's sole function is as a courier to ferry genetic material to females before dying, in others, young males are driven out from the group, to fend for themselves or die trying, in yet others species, females will consume the males after mating. And across all sexually reproducing species, only a fraction of males will win a chance at mating and passing on his genes - the rest die as genetic dead ends.
Analysis of ancestral DNA shows that men consistently fail to reproduce at anywhere close to an even 1:1 ratio to women. In fact some 4,000-8,000 years after humans invented agriculture the ratio was some 17 women for every 1 man who were reproducing (source: https://psmag.com/environment/17-to-1-reproductive-success).
History has shown that most males do not get a chance to pass on their genes.
Males are the diversity experiments for the species.
Because Males are undergo significantly higher selective pressures (high failure rates in nature), evolution has purposely tailored Males to express higher variability.
The very structure of the male DNA is built for expressing genetic variability. Males are hemizygous (XY) while females are homogyzous (XX) - if there was a mutation in the X-chromosome, it would be expressed immediately in Males, while in Females, the additional copy of the X-chromosome would mask the mutation.
Because in males, mutations are expressed immediately, the winners of those mutations (the 'good' ones which confer an advantage to the species) are then passed on to the next generation. And for every winning mutation, there are thousands of bad mutations which are weeded out (not passed on - those males are genetic dead ends). Thus does the species advance and evolve as a whole.
This expression of variability in Males has been documented in wider variances from the average (having a higher standard deviation) than when compared to Females.
The differences in variability has been documented in heights and body sizes (The Variational Tendency of Men, Man and Women: A study of human sexual characters, Havelock Ellis) as well as in intelligence (History of a biological model of sex differences in intelligence, S. Shields).
What does more variable mean? This means that the normal distributions are flatter for males than for females. Male distribution bell curves tends to have wider and broader extremes (the upper-end and the lower-end of the distribution curve) than females (example: https://images.app.goo.gl/unzNFqobMJBxEv6m7).
Men are more variable than women (and it is a crime to state such things)
In our meritocratic society, the focus is entirely on the upper-end of the distribution, as those people who are intelligent enough or physically gifted enough often climb to the highest echelons of their respective fields, whether it be sports, chess, or leadership in corporate boardrooms.
Even if the averages for males and females are the same (which they aren't; males are on average taller and have higher IQ - but let's not go there), the wider variability (flatter distribution) for males would mean that more males would be present at both ends of the distribution than females. When only looking at the upper end of the distribution (the most physically gifted, the most intelligent), males overwhelmingly dominate.
This, of course, constitutes a serious thought-crime in our gynocentric society - because how dare it be suggested that men and women are not equal at the highest positions?
One of the most prominent incidents occurred in 2005 when then Harvard President, Larry Summers, addressed the National Bureau of Economic Research Conference on the subject of gender diversity in the science and engineering professions. Summers confined his comments to "the issue of women's representation in tenured positions in science and engineering at top universities and research institutions".
His remarks were carefully chosen to be innocuous: "It does appear that on many, many different human attributes - height, weight, propensity for criminality, overall IQ, mathematical ability, scientific ability - there is relatively clear evidence that whatever the difference in means - which can be debated - there is a difference in the standard deviation, and variability of a male and a female population."
Yet those remarks generated enough outrage from women that is was sufficient to get him sacked from his position. So be careful with what you know, even if it is the truth.
Social causes of Male Disposability
Society and upbringing also plays a part in male disposability.
Boys and young men are indoctrinated and conditioned early in life to believe their role is to sacrifice for the good of others. They are made to understand that society expects them to play the role of the hero and put themselves directly into the line of danger and potentially sacrifice themselves in the process.
From birth, boys are cuddled, hugged and touched less than girls, their cries illicit a lessor response than girls and they are told by parents that "boys do not cry" and if they fall, to "rub dirt on it".
This is not new and stems all the way back to our early hominid ancestors - the attitude of disposability has been developed and is ingrained as part of human society.
Our early ancestors had roles where the women were caring for the young and staying near the fire (hearth). The greatest danger for women was during forays to gather.
The men had roles that included hunting, patrolling and guarding the perimeter and attacking rivals or repelling attacks by wild animals and intruders.
The relative danger between the roles is not subtle.
Men were exposed to decidedly more dangerous and risky endeavours and the likelihood of the man returning home was much smaller than for the woman performing her daily activities close to the hearth.
When we don't expect someone to return, it diminishes the emotional attachment to them.
We are less likely to invest our emotional attachment into someone or something that we fear may not be with us.
A 2016 study published in Social Psychological and Personality Science found that people are more willing to sacrifice men than women in a time of crisis and that they are more willing to inflict harm on men than on women.
In 2017, an attempt to replicate the Milgram experiment in Poland provided some (inconclusive, due to its small sample size) evidence that people are more willing to deliver severe electric shocks to men than to women:
“It is worth remarking,” write the authors, “that although the number of people refusing to carry out the commands of the experimenter was three times greater when the student [the person receiving the ‘shock’] was a woman, the small sample size does not allow us to draw strong conclusions.”
A 2000 study found that among vehicular homicides, drivers who kill women tend to receive longer sentences than drivers who kill men.
Another study found that, in Texas in 1991, offenders who victimized females received longer sentences than those who victimized males.
There is at least some evidence that 'women and children first' is a principle still employed during rescue efforts in natural disaster zones and some social scientists have also noted that the media is more likely to focus on female victims than male victims.
Men were the ones who were expected to sign up for the draft, to go to war and die protecting the community and country. Women, if they did volunteer, were given relatively safer and protected roles away from the front lines.
These are all deeply ingrained behaviours, woven directly into the fabric of our social consciousness. The message is clear - society conditions and expects men to be disposable.
This brings us to the key takeaways:-
Society conditions and expects men to be disposable;
There is a biological basis for male disposability and history has shown that most males do not pass on their genes.
Males are nature's way of experimenting and there is inherently greater male variability at the extremes - that means more male geniuses and also more male morons;
there doesn't seem to be anything here