At least two female designs were created for Predators but never got past the concept art stage.
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Interesting that they considered doing at least one for the film (it definitely would have counterbalanced the only human female character in the film). But I think I agree with a lot of others about the design. Honestly, it looks sort of along the lines of a lot of the fan art I've seen, where the artist attributes a lot of feminine details that are typical in human females. Honestly, if I were designing one, I wouldn't look at the typical women of Earth. I'd honestly look at professional female body builders (I mean, the Predator in the first looks sort of similar to the professional male bodybuilders of the time. I don't know if that was the production designer's idea, but it involuntarily does. With female body builders, they do have some recognizable female attributes, but they appear to gain some masculine details as well). I think you'd want to have a female Predator that could sort of keep up with the males, in both action and appearance.
Another option is that the females are very different from the males. They may not be as mobile as the males or have a different body construct (quadrupedal etc ...) More of a termite queen that's only good for reproduction and little else. That might explain why the males are the hunters, they hunt and take care of the females who can't fend for themselves.
Another option may be that Predators are hermaphrodites (like the somewhat similar Kafers in the 2300AD RPG by GDW) or may even change gender at different points in their life cycle.
Both of these make sense. Honestly, the first one would seem odd to most filmgoers (especially since the males are depicted as hardcore hunting and killing bad-asses. And to them, it'd seem odd the female Predators aren't as bad-ass as the males while human females presented in the films have been just as equally bad-ass as human males and almost as bad-ass as male Predators), but it would make a lot of sense as to why their culture hunts. But the problem with that idea of the males hunting for the females is this: it negates the point of collecting the skulls of creatures they've hunted as trophies. Plus it also contradicts why they would attempt to evolve their hunting skills by having a game preserve (as we see in
Predators), unless the hunting and trophy collecting is meant to be some sort of offering to the females (sort of like how human men will buy jewelry for human women).
The idea of hermaphrodites reminds me of something brought up in the first
Jurassic Park film, about how some species of frogs interchange their sex (which, due to the DNA being use in the dinosaurs, allowed a group of all females to breed). So, that'd make a bit of sense that an alien species would do so. The thing is that the films never really addressed if they were reptilian in nature or not (though one can assume they are due to how they appear).
Thermal imaging cannot see thru mud, period. It is an issue of density of material and insulation thickness. The Predator would have absolutely picked up every inch of space that Arnold touched though. Residual heat lasts much longer than you would think. The sensor picks up the variation in temperature from the ambient temp of the immediate area.
As far as the females go, I believe their society has been described as Matriarchal, with the males competing for the females. This comes from the novelizations, comics, etc.
So, for the thermal imaging, you're saying it is due to the mineral composition, but the thickness of it as well? That'd make a lot of sense (kinda like how you can add foam or some sort of cloth material a room to cut down on the acoustic reverberation that would occur if you were to talk).
Yeah, the society stuff is from the expanded universe stuff that I made mention of before. But even with a lot of tie-ins and their direct involvement, sometimes some details don't sync up due to the point of view of the individual working on it, so we are not sure how much could be considered canon, if it could be considered canon at all.
Actually, as I recall, there was one that was more slender, more 'gracile' than most of them that stood out as appearing more 'feminine' to me and my husband. It was subtle, but noticeable to us.
I've looked at pictures from that scene, but I didn't notice any one of them stand out as being slightly feminine. I could be wrong of course.