Xenomorph evolutionary pressures

[Majin Gojira]

kind of a sucky defense if it involves you bleeding before the predator is told off.

Doesn't a bee die after it stings someone? It could be an "altruistic" defense mechanism for the hive, or a deterrent (predators realize they're inedible and don't attack them).

Bees only when they stings a fleshy target. Insects and other arthropords can be stung multiple times. This is because a bee's stinger is barbed, to saw through carapace, but it gets hooked on flesh.

[Junghalli]

As fpr a reasonable explanation for their existence from a natural origin; perhaps they fit perfectly well into their hypothetical home ecosystem? Perhaps acid blood is a common trait or they were the only ones to evolve it. If you'd given them an ecosystem like Earth at any point up to the last couple of thousand years, they'd easily be the top predators.

I was always partial to the theory that they evolved on some really nasty planet, sort of like Catachan.

[DPDarkPrimus]

After a xeno is dead, the blood becomes neutralized, so whatever causes it to be acidic is an active process in its biology. It could be that the acidity of its blood is merely a by-product of biological processes in the body, and that it resulted naturally through evolution not as an offensive or defensive mechanism.

[TithonusSyndrome]

The bioterror suggestion seems more than an idle one, considering the beast was designed by freaking H.R. Giger I'd be hard pressed to come up with a better in-universe explanation. It practically screams for it.

[DPDarkPrimus]

The look of the xeno in the first film was done by H.R. Giger, but not the fact of the acid blood.

[DPDarkPrimus]

Clarification: The acid blood was in the script, while the actual look of the creature was never clarified by Dan O'Bannon and was left up to the imagination of those doing production.

[Vendetta]

I was always partial to the theory that they evolved on some really nasty planet, sort of like Catachan.

You'd think they'd use something less vulnerable to environmental hazards than the facehugger stage in that case though.

[Alyrium Denryle]

Wow. I need to check this forum more often. You guys are talking about three of my favorite things. Evolution, Xenomorphs, and by extension Parasites.

After a xeno is dead, the blood becomes neutralized, so whatever causes it to be acidic is an active process in its biology. It could be that the acidity of its blood is merely a by-product of biological processes in the body, and that it resulted naturally through evolution not as an offensive or defensive mechanism.

The energy involved in producing acid, even as a by-product, is high enough that it would be selected against.

Bees only when they stings a fleshy target. Insects and other arthropords can be stung multiple times. This is because a bee's stinger is barbed, to saw through carapace, but it gets hooked on flesh.

Bees are actually specialized to combat mammalian targets. The venom gland keeps pumping toxin even after it is ripped out.

50/50 fanon/Word of God is that they were a terror weapon designed by the Space Jockeys. Ridley Scott seemed to think so. (Their "weapon" value seems mostly to have been squick factor, they're not designed to be effective as a weapon, just as unpleasant as possible)

Sources for that? Because frankly I dont think it possible to build them from the ground up. Modifying an existing organism yes, but from the ground up, no. Hell when you create a bio weapon, you want it to be as host-specific as possible. You dont want it escaping from your primary target and hitting un-intended areas or getting loose in your own territory. So you would not ever, if you were sane design some generalist parasite that has defense mechanisms up the wazoo, a genetic memory, and the ability to incorporate host DNA to give itself interesting new traits. Hell: Fucking: No

Puffer fish are very toxic - but only when eaten. As are monarch butterflies. Gee, that's an amphibian, a fish, and an insect that have all evolved that same "I have to get hurt/killed before this works" defense mechanism. It may suck for the individual, but clearly it can benefit a species.

Naive group selection Bad. Kin Selection and Multi-Level Selection good.

What is going to decide this is ecological constraints. These are colonial parasitoid/predator. You can think of them like yellow jackets. They raid bee hives, killing every worker and bringing the larvae back to feed their own sisters.

They throw wave after wave of Soldier/Worker morphs at whatever species it is that they are attacking, not only are the defenders casualties dragged back to the nest and face-hugged (barring what the workers need to feed on) but even the Xenomorphs own casualties hurt their prey. Moreover they all seem to be pretty much clonal (phenotypically plastic, but clonal. Any individual face hugger can implant either a queen or a worker depending on the conditions) so there is no fitness loss if an individual dies. The entire group benefits from it, because they are all genetically pretty much identical.

It is fucking brilliant.

They seem to specialize in attacking other group-living prey. This is why even the face huggers have acid blood. The prey's conspecifics try to help and they get injured or killed, probably without appreciably hurting the face-hugger, who is pretty much done with their job once they get their little copulatory organ down the prey item's throat (the actual transfer of the Xeno larvae probably does not take very long, having the face hugger attached probably serves to protect the host/early larvae during the period in which the larvae is hooking itself into the circulatory system, it also serves to immobilize the victim so it cannot contribute to group defense)

Or maybe they have bright-colored warning tones, but just not in a wavelength humans can see. Maybe most of the things that prey on them in their natural environment see in UV or IR so their striking colorations are in those wavelengths.

The acid blood is offensive, not defensive... They dont use if when being eaten, they use it when they are attacking their own prey. They also are smart enough to use it as a tool....

Or it simply knocked her out with a swift hit. The venom thing you are suggesting sounds pretty contrived, especially since easier solutions are availabe.

But they are not easier. The face huggers use a sedative to keep the prey from struggling. It is not unreasonable for the adult workers to do the same thing. Especially because they dont seem to use their outer-jaws for anything but looking menacing. They always seem to kill and feed with the inner jaw. Yet, the outer jaw is dripping with a very interesting saliva. I would posit that that is venom, and like gila monsters it is channeled into a wound by the teeth, and acts as a non-lethal neurotoxin. Works just long enough to get the prey back to the nest and cocoon them. Otherwise, the "waking up just before implantation" thing would not be consistent.

Yes, I really do love these things.

As for their apparent ability to incorporate hose DNA... I will call it pseudo-transformation. Transformation in bacteria is basically picking up random bits of genetic material from the environment... What the xenos do is probably non random. It is probably a mechanism that allows them to have very broad host preferences and adapt to any number of different conditions In other words, wherever they evolved, they have been in space a long time. Probably what they do is they somehow incorporate genes from the regulatory mechanisms of their hosts development. How they do this, I dont know. But it probably carries down from whatever the queen's host was. I will have to watch Alien 3 again to make sure... because it is possible that the workers do the same thing, but perhaps to a lesser extend (I kinda want to key out different morphs...)

[DPDarkPrimus]

After a xeno is dead, the blood becomes neutralized, so whatever causes it to be acidic is an active process in its biology. It could be that the acidity of its blood is merely a by-product of biological processes in the body, and that it resulted naturally through evolution not as an offensive or defensive mechanism.

The energy involved in producing acid, even as a by-product, is high enough that it would be selected against.

When not active, the xenos curl up and hibernate, to conserve energy. Also, if you go by the lifecycle interpretation Ridley Scott had in the first film, a Xeno's lifespan was measured in days, so rapid metabolism and high energy cost would fit in that.


The actual origin of the xenomorphs is still speculation. Being on the Space Jockey ship heavily suggests that, at the very least, the Predators were not the first sentient species to find them, and if they were engineered, the Jockeys would have been more likely to have done it.

The novels all say that the xenos only attack you if you resist and pose a threat to them. Otherwise they will incapacitate you and carry you back to the hive for impregnation.

The acid blood is offensive, not defensive... They dont use if when being eaten, they use it when they are attacking their own prey. They also are smart enough to use it as a tool....

The acid serves as a deterrent to injure them, and it also incapacitates so they can take the victim back to the hive. As for "they are smart enough to use it as a tool", the scenes in Alien Resurrection can't be treated as normal for xeno behavior, as they are genetically different from the xenos we see in the previous films.

[Terralthra]

They seem to specialize in attacking other group-living prey. This is why even the face huggers have acid blood. The prey's conspecifics try to help and they get injured or killed, probably without appreciably hurting the face-hugger, who is pretty much done with their job once they get their little copulatory organ down the prey item's throat (the actual transfer of the Xeno larvae probably does not take very long, having the face hugger attached probably serves to protect the host/early larvae during the period in which the larvae is hooking itself into the circulatory system, it also serves to immobilize the victim so it cannot contribute to group defense)

Source for that? My understanding was that the facehugger wraps its tail around the implantee's throat and strangles it to unconsciousness, not that there is any chemical sedative.

[Alyrium Denryle]

They seem to specialize in attacking other group-living prey. This is why even the face huggers have acid blood. The prey's conspecifics try to help and they get injured or killed, probably without appreciably hurting the face-hugger, who is pretty much done with their job once they get their little copulatory organ down the prey item's throat (the actual transfer of the Xeno larvae probably does not take very long, having the face hugger attached probably serves to protect the host/early larvae during the period in which the larvae is hooking itself into the circulatory system, it also serves to immobilize the victim so it cannot contribute to group defense)

Source for that? My understanding was that the facehugger wraps its tail around the implantee's throat and strangles it to unconsciousness, not that there is any chemical sedative.

They would wake up as soon as the face hugger started breathing for them.

[Terralthra]

They seem to specialize in attacking other group-living prey. This is why even the face huggers have acid blood. The prey's conspecifics try to help and they get injured or killed, probably without appreciably hurting the face-hugger, who is pretty much done with their job once they get their little copulatory organ down the prey item's throat (the actual transfer of the Xeno larvae probably does not take very long, having the face hugger attached probably serves to protect the host/early larvae during the period in which the larvae is hooking itself into the circulatory system, it also serves to immobilize the victim so it cannot contribute to group defense)

Source for that? My understanding was that the facehugger wraps its tail around the implantee's throat and strangles it to unconsciousness, not that there is any chemical sedative.

They would wake up as soon as the face hugger started breathing for them.

That doesn't qualify as a source. Do you have any evidence that it's not done via constricted air passage?

[Seele]

The acid serves as a deterrent to injure them, and it also incapacitates so they can take the victim back to the hive. As for "they are smart enough to use it as a tool", the scenes in Alien Resurrection can't be treated as normal for xeno behavior, as they are genetically different from the xenos we see in the previous films.

We see an Alien in the 1st AvP use it's acid blood from the wound from the cut off tail against the Celtic Predator.

[Alyrium Denryle]

Source for that? My understanding was that the facehugger wraps its tail around the implantee's throat and strangles it to unconsciousness, not that there is any chemical sedative.

They would wake up as soon as the face hugger started breathing for them.

That doesn't qualify as a source. Do you have any evidence that it's not done via constricted air passage?

I dont need a source you fucking idiot. It is a logical inference, if they use a constricted air passage they will not be able to maintain hours of unconsciousness in the host without the host dying from hypoxia. Do you need to learn to read and go take a class in basic biology, you know, where they tell you that humans breath air and hours of unconsciousness due to oxygen deprivation will lead to a rather permanent sort of unconsciousness. Even IF they initially strangle their host, something they cant rely on for all their potential hosts, they cant maintain unconsciousness for that long without KILLING their host, and because we know they force air into their hosts lungs to keep it alive, we know they do not in fact do that. A sedative is required, no other option is available to the 2 kg face hugger

[DPDarkPrimus]

While on board the USS Sulaco traces of an unidentified compound was recorded in Lieutenant Ripley's body during the implantation process. There was no record of such a compound present in her system at the time of entering hypersleep, nor was this compound recorded as being present in either of the other two cryo-tubes that were supporting humans. The only logical hypothesis is that the compound was introduced by the Alien larva to ensure the host would remain in a comatose state.

Good enough for the Anchorpoint Essays, good enough for me.

[Alyrium Denryle]

When not active, the xenos curl up and hibernate, to conserve energy. Also, if you go by the lifecycle interpretation Ridley Scott had in the first film, a Xeno's lifespan was measured in days, so rapid metabolism and high energy cost would fit in that.

What I mean is that it wont work as a by-product. Making acid is expensive, even for an organism who has a lifespan measured in days, that is too much. When an animal has a short lifespan they devote less energy to their metabolic processes and more into reproduction or whatever it is they do during those couple days.

If they are actively making acid, it is because it was selected for specifically.

Also: how do you figure the lifespan is only a few days? They develop quickly, but so do ants once they eclose from their pupal state, but their lifespan is pretty long for an insect.

The novels all say that the xenos only attack you if you resist and pose a threat to them. Otherwise they will incapacitate you and carry you back to the hive for impregnation.

Well considering the reality of natural selection (read: prey animals ALWAYS resist in some way, even useless ways) that is a useless distinction.

The acid serves as a deterrent to injure them, and it also incapacitates so they can take the victim back to the hive. As for "they are smart enough to use it as a tool", the scenes in Alien Resurrection can't be treated as normal for xeno behavior, as they are genetically different from the xenos we see in the previous films.

A deterrent only serves as a deterrent against predators that are already savvy, or who have a sensory bias to aposematic coloration due to selection (if you dont shy away from high contrast black on red coloration you dont live long enough to procreate)

Xenomorphs do not show aposematic coloration, they do not display unken reflexes, nothing. There is no reason to suspect it is purely defensive in nature from anything that is observed.

If you want an acid to incapacitate and serve as a deterrent you dont produce an acid that eats through metal in seconds, a few drops of which disintegrates someones arm. That is not an "incapacitant" it evolved to kill. Very specifically.

[DPDarkPrimus]

When not active, the xenos curl up and hibernate, to conserve energy. Also, if you go by the lifecycle interpretation Ridley Scott had in the first film, a Xeno's lifespan was measured in days, so rapid metabolism and high energy cost would fit in that.

What I mean is that it wont work as a by-product. Making acid is expensive, even for an organism who has a lifespan measured in days, that is too much. When an animal has a short lifespan they devote less energy to their metabolic processes and more into reproduction or whatever it is they do during those couple days.

If they are actively making acid, it is because it was selected for specifically.

Also: how do you figure the lifespan is only a few days? They develop quickly, but so do ants once they eclose from their pupal state, but their lifespan is pretty long for an insect.

I said I was basing it off the lifespan as envisioned by Ridley Scott. He has stated that the lifespan of the xenomorph was meant to be only a few days. It dragged off the crew of the Nostromo, implanted them so they would turn into eggs for its own hive, and when Ripley found it at the end of the film, it was curled up ready to die.

The novels all say that the xenos only attack you if you resist and pose a threat to them. Otherwise they will incapacitate you and carry you back to the hive for impregnation.

Well considering the reality of natural selection (read: prey animals ALWAYS resist in some way, even useless ways) that is a useless distinction.

Hence the qualifier "and pose a threat". Just flailing your limbs about and shouting isn't going to do much to them, but if you are firing a gun at them, then they'll take you down.

If you want an acid to incapacitate and serve as a deterrent you dont produce an acid that eats through metal in seconds, a few drops of which disintegrates someones arm. That is not an "incapacitant" it evolved to kill. Very specifically.

When did it "disintegrate" someone's arm? I'm having trouble recalling this. And just because it's so volatile to humans doesn't mean it was so terribly dangerous to whatever was around on the xeno's home planet.

[DPDarkPrimus]

In fact, an ecology of creatures that were naturally resistant to acidic levels would necessitate an extremely volatile acid to be effective.

[Spanky The Dolphin]

If you want an acid to incapacitate and serve as a deterrent you dont produce an acid that eats through metal in seconds, a few drops of which disintegrates someones arm. That is not an "incapacitant" it evolved to kill. Very specifically.

When did it "disintegrate" someone's arm? I'm having trouble recalling this.

He's deductively reasoning (correctly) that if a small spill of their blood can rapidly eat clean through two deck layers of a starship then only a few drops should burn through human flesh and bone with almost no effort.

[Alyrium Denryle]

If you want an acid to incapacitate and serve as a deterrent you dont produce an acid that eats through metal in seconds, a few drops of which disintegrates someones arm. That is not an "incapacitant" it evolved to kill. Very specifically.

When did it "disintegrate" someone's arm? I'm having trouble recalling this.

He's deductively reasoning (correctly) that if a small spill of their blood can rapidly eat clean through two deck layers of a starship then only a few drops should burn through human flesh and bone with almost no effort.

And they did, in AVP: Requiem. Opening face-hug with the father. Not much of one's blood de-limbed him in a matter of seconds.

[Alyrium Denryle]

In fact, an ecology of creatures that were naturally resistant to acidic levels would necessitate an extremely volatile acid to be effective.

Acids tend to be very very interesting for organic compounds. Life would not have originated on a planet with such conditions.

[Galvatron]

While on board the USS Sulaco traces of an unidentified compound was recorded in Lieutenant Ripley's body during the implantation process. There was no record of such a compound present in her system at the time of entering hypersleep, nor was this compound recorded as being present in either of the other two cryo-tubes that were supporting humans. The only logical hypothesis is that the compound was introduced by the Alien larva to ensure the host would remain in a comatose state.

Good enough for the Anchorpoint Essays, good enough for me.

Where does it state that? Ripley wasn't impregnated while still on the Sulaco. That was Newt.

[Alyrium Denryle]

While on board the USS Sulaco traces of an unidentified compound was recorded in Lieutenant Ripley's body during the implantation process. There was no record of such a compound present in her system at the time of entering hypersleep, nor was this compound recorded as being present in either of the other two cryo-tubes that were supporting humans. The only logical hypothesis is that the compound was introduced by the Alien larva to ensure the host would remain in a comatose state.

Good enough for the Anchorpoint Essays, good enough for me.

Where does it state that? Ripley wasn't impregnated while still on the Sulaco. That was Newt.

Newt never was impregnated, her body was clean in Alien 3. However a neurotixin is required to keep the hosts quiet at pretty much all stages of implantation, from capture through to chest-burst.

[Vendetta]

Sources for that? Because frankly I dont think it possible to build them from the ground up. Modifying an existing organism yes, but from the ground up, no. Hell when you create a bio weapon, you want it to be as host-specific as possible. You dont want it escaping from your primary target and hitting un-intended areas or getting loose in your own territory. So you would not ever, if you were sane design some generalist parasite that has defense mechanisms up the wazoo, a genetic memory, and the ability to incorporate host DNA to give itself interesting new traits. Hell: Fucking: No

Ridley Scott's director commentary on the Alien DVD. Hence Word Of God, not actually canon, but the intent of the director.

[Alyrium Denryle]

Sources for that? Because frankly I dont think it possible to build them from the ground up. Modifying an existing organism yes, but from the ground up, no. Hell when you create a bio weapon, you want it to be as host-specific as possible. You dont want it escaping from your primary target and hitting un-intended areas or getting loose in your own territory. So you would not ever, if you were sane design some generalist parasite that has defense mechanisms up the wazoo, a genetic memory, and the ability to incorporate host DNA to give itself interesting new traits. Hell: Fucking: No

Ridley Scott's director commentary on the Alien DVD. Hence Word Of God, not actually canon, but the intent of the director.

may have been the intent of the director, but it is not plausible in-canon. Anchorpoint Essays be damned. This guys conclusions are... in some cases genius, in others rather special.