Evolution - why human vulnerability ?

The thread on “why monkeys haven’t evolved” brought to mind another area of evolution theory that remains hazy for me :

If evolution selects for survival, why are humans bodies so vulnerable to harm from their environment ?

AFAIK the only big physical advantage we have is longevity. If we drink out of puddles we become sick and get eaten by saber tooth tigers. If we expose our skin to strong sun we burn. We are easily killed by cold. We have no sharp claws, can’t see in the dark, can’t sniff out predators, have weaker muscles and more fragile bones than many other primates. Other animals our own size can generally kick our ass in a fight etc.

When we get dropped, we break.

I understand the arguments whereby these physical limitations have created a need for superior tool use and communication skills, thus leading to our success, but what I don’t get, is why evolution would have selected for these very apparent physical vulnerabilities.

Are we purely an ‘evolutionary accident’ whereby an otherwise severely survival impaired strain developed the spark of intelligence, barely escaped the jaws of doom, somehow overcame its daunting limitations and went on to dominate its environment ? (I would call this the plucky monkey hypothesis)

Have we, through millions of years of selection processes, somehow prolonged our infantile vulnerability phase to a lifelong state ? (The Peter Pan hypothesis)

Hey, that would mean that ‘social darwinism’ was all about society being a good parent to the individual !

What do you all think ?

Preacher man tells me we were created in gods image. He tells me these scientists don’t know diddly. Praise be the lord. And always vote democrat.

Apparently the big dangerous outside isn’t that dangerous that we couldn’t survive without those vulnerabilities. (otherwise we wouldn’t have. Logical innit?)

From our modern homes it is a daunting prospect to confront a lion but, judging from severeal docus, a pride of lions is easily scared away by a couple of people, that approach them loudly and boldly.
Maybe the same went for sabretooths.
In real life actual fights with other animals are not that frequent as to wipe out the group.

Well, there’s another human advantage. Endurance. We’re not strong, but we can literally run things to death. That’s how they used to hunt. Chase a herd of deer. Deer run off. Follow the herd. Deer run off. Follow the herd. Keep doing it. Third or fifth time, the deer aren’t going to be running off very fast anymore.

Course, there’s those hands things, and the fact that we can work in groups, communicate over distances… plan, you know, all that.

You’re probably right Latro, since apparently we have ‘prevailed’.

My question is more along the lines of -

If we accept the notion of natural selection, and the common primate ancestor, why has evolution ** ‘de-selected’** a number of apparent physical strengths in arriving at modern humans ?

(PS Southern Dem does that mean that God shares these physical weaknesses with us ?)

To simply state it, evolution doesn’t only select for survival. You could live until you were a million, but if you don’t have any offspring, your genes will not be ‘selected’.

It’s your genes, and not you, that get’s naturally selected for fitness (IIRC). Those genes which help an organism survive and have been passed on to offspring are those that will survive.

Basically, IIRC.

Also, the other posters are correct in that the human body is adequate to do the job of surviving.

There is actually a big truth to what you way. Humans are sort of children, physically, by the stanards of the great apes. Our skeletel and muscle structures are not so well developed - its as if we matured into, well, late childhood.

I suspect this is due to the pressures of the brain. Our nervous systems take much, much more energy to feed. Energy that isn’t going to physical growth. Intellect was a better measure of survival than brawn - after all, it never mattered if Gork could beat up Og, if Og was smart enough to make his own spear and stab Gork first. Ok, its a crude example, but forgivey moi.

Basically, those traits were deselected because they werent important.

But since I’m also religious, I also say they were de-selected because God decided they would be.

Asteroide dude,

Yeah, this evolution thing has selected our brains/intelligence/dexterity etc. All very useful and all that.

In fact, so useful that our physical vulnerability has become irrelevant. We built weapons to hunt, so we didn’t get killed despite our physical weakness. We found ways to shelter from the elements, so we survived even though a cold human may not have survived the winter. Our physical weaknesses became irrelevant as we found ways to overcome them without removing them. So there was no need for evolution to ‘deselect’ them.

All good practice for our evolving minds.


None of that deals with why we LOST advantages. Which would survive better: Smart biped with near current human physique and senses, or a being with the same smarts and biped also having increases strength agility and/or senses?

At some point in our evolution we had to have some survival traits that weren’t smarts based. We weren’t (and by “we” i mean any ancestor back to single cells) always smart.

Somehow, at some point, some primate-like organism started breeding smarter more upright offspring. But in doing so, they lost strength, speed, senses, toughness, agility, and perhaps any number of other things.

Part of me wonders if the real problem isn’t that we aren’t capable physically of greater things, but that our brains get in the way. Do you think a gibbon really worries that much about falling when brachiating? Probably not, he probably just does it. We on the other hand have to really practice and think about it. Things like fear of falling or lack of desire to practice may keep us from reaching that potential. Humans can run for long distances, lift large weights, be very acrobatic, be amazingly accurate. The main difference is that we have to THINK about doing these thing, and WORK at doing them. Whereas animals just do it.

Humans are neotenous - we retain juvenile traits longer. This gives us bigger brains in proportion to our bodies, allows us to learn for a longer period of time, and gives us some physical traits that are useful like bare skin and a long lifespan. As far as drawbacks, it takes us a long time to reach sexual maturity, and we are helpless for a far longer period of time in childhood - our young are essentially born premature, and it takes another year and a half after birth to reach the level of physical maturity of a newborn chimp.

What I think is interesting is neoteny is something that we breed for when we try to domesticate animals - we pick the ones that are least aggressive, that haven’t developed adult territoriality, to breed. Maybe we, as highly social plains apes, domesticated ourselves.


Oh, yeah, we’re *SO vulnerable! Every other species of animal on the planet hunts us with impunity. We can’t track down and kill a single other species for food or even for grins. Yup, so incredibly vulnerable we are.

Self- domestication

Could it be that we humans have been protecting our physically weak (less adaptive), thus permitting those genes to be transmitted, for long enough to affect the selection process ?

I’m thinking in terms of ‘Glog can’t leap from tree to tree too good, but he knows how to make fire, so let’s help him survive’.

Badtz - what would be the evolutionary advantage of bare skin ? Is this simply an example of a larger phenomenon of neoteny (new word for me) - unintended side-effect of a self domestication program ?

Bare skin allows us to get rid of heat better, IIRC. That allows us not only to survive in some harsh climates, but become hunters in the manner mentioned by E-Sabbath. I believe it is called cursorial hunting, and getting rid of exess heat is a major factor.

I think the basic premise here, that strength/claws/etc is the only way to thrive is flawed. There are many roads to successful species, and nothing is actively directing the process. Humans developed larger brains and tool manipulation, so there was no need for the other “features”. They would probaby hurt in the long run, taking energy from the more effective attributes of human development.

Looking back at it, that still wouldn’t explain why the ‘physical vulnerability’ traits have become dominant unless we accept that the (smart and weak) are favored over the (smart and strong) by either evolution or our putative self-domestication program.

It’s possible that smart and strong isn’t possible. It just takes too much energy to be sustainable. Having large amounts of muscle and fast reflexes and teeth and claws takes energy, and the environment we developed in possibly couldn’t support that much. Our most successful ancestors were the ones who had greater mental strength, and the ability to hunt animals over long distances.

And again, why would there be pressure to develop physical traits when we were successful already. Evolution doesn’t favor anything specific. It’s whatever works in the environment.

I’m not sure what the “self-domestication program” is. Care to elaborate?

my worthless opinion:

the human body is designed for flexible response. A rhino has an advantage of a thick skin, but has to carry the darn thing around. Similar problems occur with other animal design.

Humans have nifty hands, stereo vision, etc. and intelligence to adapt them to different situations. Having claws or fangs would be a disadvantage in most situations.

Were these traits actually de-selected.
If Lucy is indeed a direct ancestor, I think we might conclude that we actually did get bigger and stronger.

Our ancestors weren’t big strong gorilla type apes but rather frail creatures from the start.
There were other homonids that were indeed even stronger but I think it was us that de-selected them from evolution, because we are more agressive. (IMHO, of course)

my worthless opinion:

the human body is designed for flexible response. A rhino has an advantage of a thick skin, but has to carry the darn thing around. Similar problems occur with other animal design.

Humans have nifty hands, stereo vision, etc. and intelligence to adapt them to different situations. Having claws or fangs would be a disadvantage in most situations.


Well, I guess that’s the crux of it, if it could be demonstrated that ‘smart’ and ‘strong’ can’t co-exist in an individual, the question would go away - do you know of any work that addresses this ?

As you noted, what puzzles me is not that we havent selected for 25 inch horns (apparently we don’t need them), it’s the dissapearance of some of the more robust features of our putative ancestors (this would require a ‘de-selective’ evolutionary function for no longer essential, but somewhat advantageous features - eg heavier bones).

The self-domestication notion stems from a post by Badtz Maru about 5 back likening the extended human childhood to features we breed for in domesticated animals (‘neoteny’).
jsleek - are you suggesting we may simply have evolved to a sort of ‘tabula rasa’ condition, with minimum physical attributes for maximum adaptability ? Interesting - and it’s certainly true that a rhino would have a hard time driving a car - the issue I might have with this notion is the time frame. Have we really been living in a controllable environment for long enough that this could have come about simply as a result of ‘natural selection’ with no game plan ?

Latro makes a good point – The hominids that are apparently on the line to humans used to be small creatures, under 4’ tall at adulthood. It seems their defensive methods in the wild would have been alertness, sneakiness and endurance, and that our bloodline was never physically fearsome.

After genus Homo appears, the apparent peak of “natural” physical muscularity were the Neanderthals – themselves relatively recent, in fact contemporary with H. sapiens for almost 100K years – who had to rough it in the wilds of ice-age Eurasia, so they had better be tough, and their braincases were about as big as ours. However, even before the ice receded completely, in came “us”, who though physically weaker (a) bred much more prolifically (b) had better spears © were better organized.

But part of it has to do with a misconception of how evolution works. Sure, smart AND strong would be “better”. But evolution does not give a damn about “could be better”, it selects and propagates whatever worked in the particular case. Physically “weaker” H. sapiens, with sharper wits, relatively high endurance (when healthy), a long lifespan for an animal our size if disease or violence don’t nail us, a higher birthrate than Neanderthals, a social structure that aids in protecting and caring for the children and elders within the tribe, and a mean streak a mile wide to anything and anyone outside the tribe, endured and prevailed and never needed to face selection based upon physical brute strength. That primitive life required you to be physically fit is a different story – surely very few Cro-magnon lived to adulthood as lard-ass layabouts – but the most physically fit caveman would be history if he ever had to go mano-a-mano with a bear, sans spear.