Why are there (roughly) an equal number of males and females?

Question

From an evolutionary/biological/racial propagation perspective, wouldn't it make sense that there would be a much higher proportion of females in the population of any species?

Also, just to be clear: I'm aware that the human birth sex ratio is something like 105 males to 100 females—that's not what I'm talking about. The question is, why is it not something like 10 females to 1 males, since one male can impregnate many females.

This question is to do with ANY species, not just humans.

Answer 1

The accepted theory for the 1:1 sex ratio is that any diversion from the 1:1 ratio would cancel itself out (Dusing-Fisher theory). I quote the below website:

The sex ratio argument, modernized and simplified a bit, goes like this. Natural selection is about reproduction. A gene affecting sex ratio does not affect your number of offspring; it simply shifts those offspring between the categories of male and female. But this allocation can affect your number of grandchildren if sons and daughters have different average reproduction. Düsing's key insight was that the total reproduction of all sons in the population has to equal the total reproduction of all the daughters, which follows from the fact that each grandchild has a father (one of the sons) and a mother (one of the daughters). If we let the total number of grandchildren, sons and daughters in the population be G, S and D, respectively, then the average reproduction of a son is G/S and the average reproduction of daughter is G/D. This means if there are more daughters than sons in the population (D > S), the average daughter will be less successful and mothers will be selected to make more sons (Figure 1). Conversely, if there are more sons than daughters (S > D), their average success will be lower, and selection will favor mothers that produce more daughters. Because the total reproduction of each sex is equal, individuals of the rarer sex have greater average success, and parents who produce more of the rare sex will have more grandchildren. This produces a stable equilibrium at S = D and accounts for the widespread occurrence of 1:1 sex ratios in nature.

Answer 2

I don't think so. If this were true, then a smaller number of men would father the children born. That second generation would have a smaller mating pool to choose from, because many of them would be paternally related. The even split allows for more variety in offspring, instead of a few men fathering all the children and limiting the gene pool. Since a female could produce offspring from a differant male on each breeding, then the population is even more diversified and inbreeding is less likely.

EDIT: Somebody brought up that worldwide more males are born than females to the human race. Well, this may be true, but considering that many countries out there have problems with large amounts of illegal female infantcide/feticide, this may be a skewed statistic.

Answer 3

herds are usually controlled by limiting the number of females in the herd. For example 100 cows and 100 bulls will make 100 calves. 100 cows and one lucky bull can also make 100 calves. The way to limit overpopulation or over production is to limit the number of calves.

Bees usually have a much higher percentage of females as you suggest. The drones are not hive keepers, queen tenders, soucts, guards or even collectors. They only mate and that is their only function. Although I did read some research that indicates hives with a higher percentage of drones can actually have higher production that a nearby hive with a lower number of drones. Maybe bees have figured out its good to keep a few males around. When an extemely difficult winter season is approaching, the bees will force out the drones as really only a few are required to propgate which proves your theory of natural selection and a higher percentage of females.

Even in humans, the statistics indicate that more males are born than females. By about year 20 its even and male/femal ration declines from there. This is due to wars/ dangerous work taken on by males moreso than females.

Answer 4

It's true that in nature sperm are plentiful and eggs are few. But this biological constant doesn't necessarily correlate toward favor of the females as an instrument of reproductive stasis. The preservation of most sexually reproducing species for the eons life has existed seems to indicate that life favors gender parity.

Answer 5

that is only the regulations of danger. you could evaluate the regulations of danger a creation of God even nonetheless it won't coach His existence to every physique who would not have faith. The numbers are not balanced on small scales. Many families have all boys or all females or maybe small cities could have many extra of one intercourse. that is basically once you seem at rather extensive numbers of those that the numbers rather equivalent out. for my area, i think of if God have been to take a particular interest in balancing the sexes, He might opt for to the two have the numbers tournament completely or have many extra women human beings. the way issues stand now, there at the instant are not fairly adequate adult adult males to flow around yet no longer so few that we could continually flow returned to polygamy.

Answer 6

Well that's true but in ancient history all the males went off to war and most of the male population was gone.

The remaining males had multiple wives. This is documented a lot in the Bible.

Answer 7

Actually, I was once told there are more males born than females. This changes, though because males are more prone to risky activities. But I can see what you mean.

Answer 8

Probably because when you have only two sex chromosomes, then the odds of any particular sperm having one or the other is 50/50.

There seems to be no disadvantage of having one male for every female, so apparently there is no feedback mechanism to override statistics.

Answer 9

Randy G, hit the nail on the head. It is merely statistics that determine sex ratios. Try a simple F1 Punnett square to see that it is all " the luck of the draw ".

Answer 10

Actually as far as humans are concerned, there are a LOT more females than males.