I think this question would more accurately fall under an embryological or gestation category but this category seems fitting and proper enough (I know nothing).
I watched this video lecture: https://www.youtube.com/watch?v=T9znJxgY2B8
Don't waste 6 minutes if you don't have the time, but in summary as to what is important to my question from the video: (If comprehended right) Ecological instability or stress can cause a certain sex to be more economically desirable insofar that it costs the parent less to bring it to term. Dominate individuals at the top of the hierarchy can afford to take a risk in having male offspring although the likely hood of that offspring being a successfully reproducing male is small.

The full lecture isn't here obviously. It may very well be more economical to have a daughter during periods of ecological instability, but how is the mother or father to choose a sex? Is there a part missing where he should say something about environmental factors determining the likely hood of having a male or female? And how would an animal at the top of the hierarchy who can economically afford to take a risk on having a male go about SELECTING a male to bring to term? The way he spoke made it sound as if it was a conscious decision.

What you are talking about is adaptive sex allocation and I think you have hit the nail on the head here. What is the mechanism? There's a good summary of the field here, but in essence it can sometimes be advantageous (for an individual) to produce offspring at a sex ratio that differes from 50:50.

https://en.wikipedia.org/wiki/Sex_alloc … _decisions


Statistically speaking there is evidence that this occurs in the sense that sex ratios can be biased in ways that are adaptive. In some cases one can see that  - mechanistically speaking  - this should not be hard to achieve. For instance in hymenopteran insects the sex of an offspring actually depends on whether the egg was fertilised or not, something that could be under maternal control. So to the extent that a bee is "conscious" then yes it could be a decision in teh sense you mean.

In many vertebrates with chromosomal sex determination it is harder to see how primary sex ratios can be manipulated. For me this raises some question marks over whether it happens at all in birds and mammals although there are some striking sex ratios to explain if it doesn't.  Interestingly, think there is little evidence for it in turtles or crocs that have temperature dependent sex determination (so in priciple a femnale could "choose" to lay a nest in the sun or the shade!).

So, yes it happens, but how is still quite an unknown!