How big can hominids get?

Factual Questions
1

Related to an earlier thread I posted in Cafe’ Society for a story I’m writing.
I’d like to include some type of troll or giant in my fiction but I am trying to conform somewhat to natural laws. So this is a two part question.

Assuming the icelandic version, (nothing more than an oversized human), how big could a being built on a human frame get and still function normally? I imagine that heart and blood pressure function might be limiting factors here.

Secondly, assuming simply an ape-like creature; and one that might travel quadruped like a gorilla, how big could this creature get and still function normally?

To help out I’ll add a few general criteria this creature must meet.

It must be omnivorous in diet.

It must be fast enough to run down human prey, OR it must be cunning enough to lay and execute an ambush style attack, OR both at once.

It should should not have to be seriously altered in terms of the musculo/skeletal system to function.

So, with that in mind, how big could we get? What would be limits on our size? What would such a creature be particularily vunerable to?

Thanks- Acid Lamp

2

Human beings, the hominid for which (of course) we have the most information, tend to have eight feet as a limit. There have been a lot of cases of adults living healthy quasi-normal lives in excess of seven feet in height, with problems developing as they approach eight feet. I’m not familiar enough with the formulae relating height to healthy weight to handle that side of the question, but apparently a normal mesomorphic build on a 7’5" person gives a weight somewhat over 400 pounds.

The large hominds of the recent geologic past were large only comparatively to the “main line” omnivorous hominids that were evidently our direct ancestors – they tended to be no larger than a large modern man, if they even attained that size.

Gigantopithecus was a giant ground-dwelling (as opposed to arboreal) ape, derived from the orangutan line but resembling a gorilla in some respects, which occupied Southeast Asia in the Pleistocene. It is known (probably in two species) solely from teeth and three jawbones. While some reconstructions suggest a size of ten feet and 1200 pounds, it seems evident from the studies of the extant material that it had an abnormally large jaw, quite likely for living on bamboo shoots (in competition with the giant panda!) and was in actuality not much larger than a large modern man.

3

Well, the Megatherium (giant ground sloth) walked upright and could be up to 20 feet in height. However, it had a powerful tail to help support its weight.

4

Well, Pro wrestling has brough us a few huge individuals with acromegaly, such as Paul Wight , Dalip Singh , and Andre the Giant . There have been some other taller individuals as well such as The giant Gonzalez. While they are the exception and not the rule they seem to get along fine athletically. Could we get significatly larger?

5

The biggest know hominid was gigantopithecus. Basically a 10 foot tall Chinese gorilla. The bad news for your story is that its diet is thought to have been almost exclusively bamboo.

6

[QUOTE=Polycarp]
Human beings, the hominid for which (of course) we have the most information, tend to have eight feet as a limit. There have been a lot of cases of adults living healthy quasi-normal lives in excess of seven feet in height, with problems developing as they approach eight feet. I’m not familiar enough with the formulae relating height to healthy weight to handle that side of the question, but apparently a normal mesomorphic build on a 7’5" person gives a weight somewhat over 400 pounds.
[/QUOTE]

Part of the problems that humans with giganticism have is that their organ systems are not adapted to such very large size. Excessive stress is placed on the heart and other systems, so giants often tend to be short-lived. It is possible that a hominid that had evolved giganticism in tandem with organ systems designed for a larger size could get somewhat larger.

I think the real problem would come in maintaining bipedalism at very large sizes. Excessive stress might be placed on the knees and ankles without a wholesale redesign. Gigantopithecus, whatever its maximum size, almost certainly was a quadrupedal knuckle-walker like other large apes rather than a biped.

[QUOTE=spoke-]
Well, the Megatherium (giant ground sloth) walked upright and could be up to 20 feet in height. However, it had a powerful tail to help support its weight.
[/QUOTE]

While the large ground sloths may have been able to rise up on their hind legs, they almost certainly did not walk that way, but shambled along on four legs. Likewise, large bears can rise up on two legs but cannot really walk any distance that way.

7

[QUOTE=Acid Lamp]
ssuming the icelandic version, (nothing more than an oversized human), how big could a being built on a human frame get and still function normally?
[/QUOTE]

That’s pretty confusing. What does it mean to not be larger than “an oversized human”? Do you mean like a tall basketball player?

One thing to keep in mind about scaling vertebrates is that weight goes up like the cube of the linear dimension whereas skeletal strength only guys up like the square of the linear dimension (since strength is related to the cross sectional area of the bones). Someone scaled up to twice normal hight would have 8x the weight, but only 4x the strength in their skeleton. Not to mention the issues related to blood pressure and artery strength and heart pumping capability.

If you assume that this “race” of beings had been evolving for 10s of thousands of years or more, then it’s possible that it had altered its skeletal structure accordingly and had made the necessary modifications to its cardiovascular system. If it’s just a big human being, then it’s going to have all the problems associated with giantism in humans today.

8

[QUOTE=John Mace]
If you assume that this “race” of beings had been evolving for 10s of thousands of years or more, then it’s possible that it had altered its skeletal structure accordingly and had made the necessary modifications to its cardiovascular system.
[/QUOTE]
If we scale the evolutionary period up to hundreds of thousands or millions of years, I see no reason not to see hominids that rivaled the size of the largest dinosaurs. T-Rex was bipedal, and ranged up to 25 feet tall. There are many reasons why they did not develop, but I don’t think you would hit a basic design limit until 25 feet.

9

[QUOTE=Fear Itself]
If we scale the evolutionary period up to hundreds of thousands or millions of years, I see no reason not to see hominids that rivaled the size of the largest dinosaurs. T-Rex was bipedal, and ranged up to 25 feet tall. There are many reasons why they did not develop, but I don’t think you would hit a basic design limit until 25 feet.
[/QUOTE]

Possibly, but T-Rex didn’t have to pump as much blood to its brain as we do-- not even close. I don’t discount natural selection’s ability to overcome all kinds of obstacles, but you can’t just infer a possible hominid size from a T-Rex size.

10

[QUOTE=John Mace]
Possibly, but T-Rex didn’t have to pump as much blood to its brain as we do-- not even close.
[/QUOTE]
Perhaps, but those jaws didn’t run on Gatorade.

I don’t think we know enough about the vascular system of T-Rex to say that it is not a reasonable inference.

11

Not an answer per se, but you might be interested in a related discussion in The Physics of Superheroes by James Kakalios. In discussing the physics of Giant-Man (Dr. Henry Pym), he suggests that one of the biggest problems with super-sized humans is that, at some point, their skeleton can’t support their weight:

Obviously, superheroes!=reality, but the book does a good job of explaining the physics of the situation in an easily-understood way.

12

[QUOTE=Fear Itself]
If we scale the evolutionary period up to hundreds of thousands or millions of years, I see no reason not to see hominids that rivaled the size of the largest dinosaurs. T-Rex was bipedal, and ranged up to 25 feet tall. There are many reasons why they did not develop, but I don’t think you would hit a basic design limit until 25 feet.
[/QUOTE]
Tyrannosaurus rex did not use plantigrade bipedal locomation as hominids (and as far as I’m aware, only hominids) do, so analogies between size of T. rex and hominids are inexact to say the least. With plantigrade bipedal posture, not only does weight have to be supported on two legs but the feet are also required to maintain balance without a counterbalancing tail; however, the muscles can’t be oriented more horizontally (as with the T. rex, or flightless birds), and so stresses on the joints are higher, limiting the practical size you can make the supporting musculature.

In bipeds, height increases linearly as surface area increases by a squared factor, and volume (and therefore weight) as roughly a cubic. So doubling the height requires four times the surface area, and eight times the mass; however skeletal strength (as previously noted) merely scales in cross-sectional area, such that you’d have to have dramatically larger bones, as well as an order of magnitude increase in supporting musculature (and correspondingly stronger joints, also making them larger by roughly the same factor) to support the same weight, which adds additional weight. This also has to be supported by the cardiovascular system, which has to be scaled to handle larger flow rates but keep pressure in a range that neither stagnates due to gravity nor creates more pressure than can be contained by delicate tissues. Oh, and it has to maintain requisite blood flow and blood sugar balance to the presumably proportionally increased volume of the brain.

So a 4m tall Homo gigantus would be very squat, with legs like an elephant, a spine like a firehose, and an enormous heart with oversized vavles and a slow, powerful pumping motion with a more limited capacity to increase blood flow on demand. You could probably intentionally design (via genetic modification and selective breeding) such a creature, but I think its lifespan would be short, intellect would be inherently limited, propensity for damage and chonic debilitating skeletal problems signficiant, and would not be competitive as a cursorial hunter; at best it would be an opportunistic hunter/scavenger like a brown bear. In nature, I suspect that human beings–already a giganticized version of our hominid predecessors–is about as tall as humans can get without major modifications. Why we are the size we are, and the advantage of bipedal plantigradism is still a hotly debated topic with no absolute consensus.

Stranger

13

[QUOTE=John Mace]
That’s pretty confusing. What does it mean to not be larger than “an oversized human”? Do you mean like a tall basketball player?
[/QUOTE]

Unfortunetly, the lore around these myths is pretty confusing as well. From what I’ve been able to piece together “troll” in Icelandic terms has three distinct meanings.

  1. A perfectly proportional human, merely many times larger than a normal man. A giant of sorts. There is a sub variety of this same being that has brutish features like a large head, huge hands and feet, and a low intelligence.

  2. A brutish person who has shunned society and now preys upon travelers and the like.

  3. More similar to the Norwegian version, a sort of man-like hairy biped that may or may not have monstrous features such as horns or extra eyes. These do not appear with regularity in traditional stories.

14

Here is an old thread on the topic: [thread=312593] Why is man (about) 6 feet tall?[/thread]

Stranger

15

[QUOTE=Stranger On A Train]

So a 4m tall Homo gigantus would be very squat, with legs like an elephant, a spine like a firehose, and an enormous heart with oversized vavles and a slow, powerful pumping motion with a more limited capacity to increase blood flow on demand. You could probably intentionally design (via genetic modification and selective breeding) such a creature, but I think its lifespan would be short, intellect would be inherently limited, propensity for damage and chonic debilitating skeletal problems signficiant, and would not be competitive as a cursorial hunter; at best it would be an opportunistic hunter/scavenger like a brown bear.
[/QUOTE]
Excellent. This is exactly the type of discussion I was hoping for. This is about the size range I was hoping for as well. At about 4m H. Gigantus is significantly separated from even the extreme human range. This also places it within the realm of a resonably funtional being. Anyone want to take a stab at the weight and relative strength of such a being? My guess is probably between 800-1100 lbs allowing for sexual dimorphism and a usual size distribution.

16

[QUOTE=Stranger On A Train]
Tyrannosaurus rex did not use plantigrade bipedal locomation as hominids (and as far as I’m aware, only hominids) do
[/QUOTE]
Macropodidae (kangaroos, wallabies, etc) usually have a bipedal plantigrade stance, although they switch to digitigrade when they’re in a hurry.

Bears are plantigrade too, but they’re mainly quadrupedal in day-to-day locomotion, so that’s maybe moot.

17

[QUOTE=Barrington]
Macropodidae (kangaroos, wallabies, etc) usually have a bipedal plantigrade stance, although they switch to digitigrade when they’re in a hurry.

Bears are plantigrade too, but they’re mainly quadrupedal in day-to-day locomotion, so that’s maybe moot.
[/QUOTE]
Strictly speaking, macropods have a tripod stance, resting back on their tails and pushing against it while crawling plantigrade. In their high speed hopping mode of locomotion, they switch, as you note, to digitigrade traction and use the tail primarily for balance. The hopping motion of kangaroos and other macropods isn’t like just jumping, either; they store the energy from a jump in specialized highly elastic ligaments and spring like a pogo stick, making that motion very efficient at high, sustained speeds. In contrast, plantigrade motion is only moderately efficient, requiring a lot of work from the leg muscles, and is better at low to moderate speeds.

Bears are plantigrade (as are elephants) but essentially quadrapedal in locomotion, even if they can stand erect and move short distances in that posture.

[QUOTE=Acid Lamp]
Excellent. This is exactly the type of discussion I was hoping for. This is about the size range I was hoping for as well. At about 4m H. Gigantus is significantly separated from even the extreme human range. This also places it within the realm of a resonably funtional being. Anyone want to take a stab at the weight and relative strength of such a being? My guess is probably between 800-1100 lbs allowing for sexual dimorphism and a usual size distribution.
[/QUOTE]
Just strictly scaling up from a 2m tall, 80kg human by a ratio of L=2 would give you a 4m tall, 649kg (1400 lb) biped. However, as previously noted, you can’t just scale up the mass as a cube without making the skeletal and other supporting structure stronger. If we assume 8 times the mass, then the strength of the skeleton needs to be increased by a factor of 8, which means the bones have to be made larger by a factor of 2L. Muscularture will also increase by a similar factor, all of which adds more weight by a similar factor, which accelerates the increase ad infinum; at some point (I’m going to guestimate 5m based upon past reading but I’m too lazy to offer an explicit cite for this) the creature will have to revert to quadrapedal locomotion, as the loads just become to massive for biological materials to sustain. I don’t think a 4m tall bipedal omnivore would be particularly viable or functional in any natural environment; I’d suspect that it would have to become a grazing herbivore with a low energy lifestyle. However, it should be noted that of the extinct megafauna of North America, the Short-Faced Bear was almost this height, and while not bipedal in standard locomotion, was plantigrade and is believed to have attacked in an upright fashion, so it’s certainly not impossible for such a large creature to occupy a primarily carnivorous niche.

Sexual dimorphism is a complex subject that can’t be reduced to strictly biomechanical roles. In mammals, dimorphism tends toward smaller females than males, but this is neither universally true, nor is there any established relationship to physical scale between species. Since there’s no apparent selective advantage in such a large size for hominids, it’s impossible to say what the effect would be on dimorphism and natal development. Bears have a delayed implantation or deferred development and a very low birth weight relative to mature weight, so again resultant size doesn’t give us a guideline for this.

Stranger

18

[QUOTE=Stranger On A Train]
Just strictly scaling up from a 2m tall, 80kg human by a ratio of L=2 would give you a 4m tall, 649kg (1400 lb) biped. However, as previously noted, you can’t just scale up the mass as a cube without making the skeletal and other supporting structure stronger. If we assume 8 times the mass, then the strength of the skeleton needs to be increased by a factor of 8, which means the bones have to be made larger by a factor of 2L. Muscularture will also increase by a similar factor, all of which adds more weight by a similar factor, which accelerates the increase ad infinum; at some point (I’m going to guestimate 5m based upon past reading but I’m too lazy to offer an explicit cite for this) the creature will have to revert to quadrapedal locomotion, as the loads just become to massive for biological materials to sustain.
Stranger
[/QUOTE]

Wow. That’s quite a bit heavier than I’d expected, thanks so much for the number crunching! That basically rules out our “scaled up human” as a viable option here. I’d no idea that due to increased bone and muscle mass and density we’d be talking probably over a ton of weight for a biped!

Perhaps a more viable option would be to restrict such a creature to primarily quadrapedal locomotion ala gigantopithecus or the mountain gorilla. The question now, is whether such an animal would have the necessity or capability to evolve a rudimentary intelligence. While it would be simple for me to hand wave everything as magick; (this is a fantasy story after all) I’d like to keep as many of my creatures within the realm of physical possability as can be achieved.

The caloric needs of such a being would be immense I’d wager. That at least could go a way to explaining a troll’s ravenous appetite and aggressive nature. Such a large animal would need to be quite territorial to control a large enough range to feed itself. Remember, such creatures come from scandinavia; not exactly a lush jungle overflowing with loads to eat at every turn.

19

But if you scale back to a 3 meter hominid, you’ve got something a lot more viable. This creature is 1.5 times as tall as a human but is 3.375 times as heavy. That means a 100 kg male human scales up to a 350 kg troll, or about 750 pounds. And three meters is well outside human variability at more than 9 feet tall. These creatures are going to walk slowly and carefully since they are 3 times heavier than a human but only 2.25 times stronger. Kind of like an overweight human. Although they should be able to run, they probably won’t do so except rarely without risking broken ankles. Their legs will be longer which increases running speed, but they’ve got more than three times human weight. Strap a 100 pound pack on your back for a simulation of their strength to weight ratio. You can run with a 100 pound pack on your back if you HAVE to, but you’re not going to do it for long.

The other important question is, what do these trolls eat? They need a lot more food than H. sapiens, and if they live in the mountains or coniferous forest or tundra where do they get enough food to keep them going? These are places where it is very difficult for large animals to gather food. They need to be able to eat things humans can’t eat or they’re going to be outcompeted by humans. Or bears, since it looks like these trolls are filling a niche already occupied by bears.

20

[QUOTE=Colibri]
While the large ground sloths may have been able to rise up on their hind legs, they almost certainly did not walk that way, but shambled along on four legs.
[/QUOTE]

You may be right, but the wiki article disagrees:

And it looks like the BBC agrees: