Fisher's principle states that there should be a 1:1 ratio between males and females born on average for a population. However, if you look at birth statistics your find that boys are slightly more likely to be born then girls. This article talks a little about how it happens

If it was truly advantageous for an even sex ratio to exist at birth I imagine we would have evolved to make that happen, by slightly favoring more female sperm or by having the processes that decides which embryos to spontaneously abort be stricter for males embryos then females. For that matter since it's more important for males to be exceptionally healthy then it is for females, since males have to compete for a mate while females don't, you would think more strict filtering for 'bad' embryos in the case of males then females would make sense anyways.

Thus I'm inclined to think that the increased number of males to females is not random evolutionary fluke, but adaptive. I'm wondering what would cause there to be a benefit for males to be slightly more common then females.

I know males are more likely to die in childhood, due to risk taking activities to impress the females, so could it be that the increase in males is due to the expectation that more males will die before reaching sexual maturity? I'm not certain I buy this logic, it doesn't seem you should favor a sex any more because it's likely to take higher risks.

I know that strong/healthy mates would prefer males and weak ones prefer females, since strong males would out compete weak males for mates it's good to have strong males that can achieve multiple mates and weak females since their guaranteed to have at least one mate. Is it possible that our increased nutrition and health of recent generations simply results in more males because our bodies judge each of us as 'healthy' compared to the standard that existed for 99% of our evolution, ie, evolution hasn't caught up with technology when judging health to decide which sex to favor?

Is there some more obvious explanation for why favoring males slightly would be adaptive in humans?

Edit: I want to stress again, I'm not asking how the bias happens. The article I linked clearly explains what causes males to occur more in terms of pregnancy. I'm asking why the bias happens. This could be evolved away in the past if it was disadvantageous, Whatever mechanisms cause there to be a bias this bias is presumably adaptive for it not to be evolved away. Both the possible duplicate and the current answer only address what causes the bias to happen today, not why it would be evolutionarily adaptive to have.


Nice question! The answer is in your linked article. I quote:

When you put this all together, it turns out more males are born because more female fetuses are lost during pregnancy.


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