Hit Points in D&D are a nebulous concept, clearly not mapped directly to how much physical damage a character could withstand (or a mid to high level fighter could withstand more physical damage than most dinosaurs!).
Gary Gygax has a great explanation of HP in the AD&D 1e DM's Guide (page 82). An excerpt:
"It is quite unreasonable to assume that as a character gains levels of ability in his or her class that a corresponding gain in actual ability to sustain physical damage takes place... Why then the increase in hit points? Because these reflect both the actual physical ability of the character to withstand damage - as indicated by constitution bonuses - and a commensurate increase in such areas as skill in combat and similar life-or-death situations... Each hit scored upon the character does only a small amount of actual physical harm - the sword thrust that would have run a 1st level fighter through the heart merely grazes the character due to the fighter's exceptional skill, luck, and sixth sense ability which caused movement to avoid the attack at just the right moment."
HP seem to be something entirely different in Mutant Future. I say this for two reasons - one, at character generation they are directly tied to the physical makeup of a character as expressed by the Constitution score (starting HP are 1d6 or 1d8 per point of CON), and two, they do not increase as the character levels up (or increase very rarely and only when CON increases in the random leveling up process).
I have been thinking about HP in Mutant Future ever since I commented on The Savage Afterworld's
Savage Managerie: Equort post that 3 HD seemed like too few for an incredibly strong, horse sized reptilian creature. Sniderman (Savage Afterworld Blogmeister) pointed out that Mutant Future's Warhorse has 3 HD, which he used as a starting point for the Equort. Opening up my copy of Labyrinth Lord, I realized that the statistics for all three horses in Mutant Future were lifted directly from Labyrinth Lord with no changes made.
This just seems wrong to me. Lets compare Labyrinth Lord and Mutant Future for a second. HP in Labyrinth Lord mean the same thing as they do in D&D. The most that a character's physical makeup as expressed by attributes can effect HP in Labyrinth Lord is + or -3 HP a level. Lets take two hypothetical 1st level fighters - one with a 3 CON and one with an 18, and assume that both have maximum HP. Their HP would be 5 and 11, respectively. The + or - 3 HP from CON illustrates the physical component of HP, and the rest has to be the skill of dodging (made more obvious when you realize that a fighter has more of these non-physically related HP than any other class, reflecting greater skills at dodging injury).
Now lets look at two hypothetical Mutant Future characters, again with a 3 CON and an 18 CON and max HP, and we see a radical difference. The 3 CON character has 18 HP and the 18 CON character has 108 HP! There is no skill of avoiding injury component here, as there are no classes and the only way HP can increase is if your CON attribute actually is increased by leveling up.
All this leads me to the conclusion that HP in Mutant Future are actually a measure of how much physical damage and exertion a character can take. The poor character reduced to 1 HP should be a bloody mess, possibly with broken bones, certainly barely able to move around. The laser blast that does 45 damage should probably leave a hole in the mutant's body. With no healing magic available, several characters have been temporarily retired in my Mutant Future game while they rest and heal up over the course of several weeks of game time.
The most interesting ramification of this understanding of HP in the Mutant Future has been with mutant plant characters that posesses the Chameleon Metamorph mutation. This enables them to change their form into that of any other plant, provided their total mass stays the same. Bozko was the first character (and the only one still active) in my campaign with this mutation, and he has came up with many creative uses of it - we have collaboratively determined that he can use pieces of his own body as ranged ammunition if he sacrifices HP, so he could, for instance, turn a section of his body into a sharp wooden branch and break it off and hurl it at someone at a HP cost determined by Mutant Lord Me. He has used this to great advantage, shaking off a few HP worth of dandelion seed tufts to form chaff to disrupt laser targeting, for instance.
This has also led to the understanding that as he is damaged, he is literally losing pieces of himself to the point that if he was reduced to 1 HP, he would only be a tiny little blob of plant matter until he slowly regrew his body! This works because we had already decided that a mutant plant with the Chameleon Metamorph ability did not have a central brain or nervous system, because the plant maintained consciousness even when in such radically different forms as a sheet of algae covering a pond or a tall pine tree. Bozko's player ran with this idea and decided that each cell of his body had all of his knowledge and memories encoded into its genetic structure, so as long as any little piece of him survived he was still sentient and could eventually regrow himself.
As a Mutant Lord, deciding that HP = Physical Damage has made it very easy and exciting to narrate events in combat. No longer do I have to restrain from describing horrendous wounds because HP are a representation of how skilled a character is at dodging; if someone takes a lot of damage, they are physically messed up. End of story. When Beyonce was reduced to 3 HP in a flame thrower attack, her body was horribly burned and her face became a mass of scar tissue.