Does the Box Jellyfish count? It has 24 eyes and no central nervous system, but it does have four “brain-like structures.” Presumably these are close to its four eye clusters.
I also saw this in Science News a while ago:
Registered subscribers only: Built for Blurs : Jellyfish have great eyes that can’t focus (5/14/2005)
Eight of a box jellyfish’s eyes have superb lenses, but their structure prevents them from focusing sharply.
(Freely accessible for the moment, although the free access message says “until 4/15/08,” nine days ago as I write this)
Maybe. But it might be like saying “any herbivore that lives in mixed grass/shrub land, and has to be able to run quickly and leap over obstacles to escape from predators, will look like a springbok”. Which sounds plausible until you see a kangaroo.
Anyway, about the OP: the heavy important bit isn’t heavy for most of life on Earth. Fish, amphibians, reptiles and early mammals have such small brains that they account for only a small percentage of the creature’s mass and are easy to bury deep within a skull that has to be large for other purposes. Large-brained mammals are the rare exception and humans most especially so. By the time primates came around, it was impossible that a major change in body plan could put the brain anywhere else. Our bodies are full of “legacy” features that no sensible designer would ever put in deliberately.
I believe you are proceeding from a false assumption. The head is, if anything, perhaps the least likely to sustain damage from the outside world. In the case of animals being preyed upon, in general, they tend to fleeing from any would-be predators in an actual attack situation (assuming they haven’t been ambushed to death, wherein it doesn’t much matter where the head is), which places the head as far from said predator as possible. In those animals which will turn to face a predator, they will typically have some sort of defenses, be they teeth, horns, extra bone, or other ornamentation which will further serve to direct predators away from the head area when making their attacks.
When organisms began moving around, they tended to congregate their sensory organs at the end which would first encounter external stimuli. This process, called “cephalization”, resulted in the “head / tail” arrangement we see in many animals today (including all terrestrial ones). Once you have sensory organs, the nervous tissue needed to organize and interpret sensory input will tend to occur in the same general area, for reasons mentioned above. Thus, we have sensory organs placed at one end of the body - the end that is likely first to interact with the world in some fashion - and the associated brain up there as well. The brain, being rather important to the well-being of most animals, will often have some sort of protection, as I mentioned above. This is especially true once boney tissues evolved.
I disagree. Sure, it’s a valid criticism against anthropomorphizing the process of evolution by natural selection, but nonetheless, it is a process that finds optimal solutions to problems. The “why” in the OP obviously refers to the constraints that have been satisfied by the search. I hold that the question makes sense to people who study these sorts of things. QED.
“Optimal”? I thought it just “found” what works. I can think of about 20 things I’d change about the human body if I were designing it, in terms of chronic pain and discomfort, starting with the knees and ending with these ridiculous fatty pads I have over my pectoral muscles. But the fact is that for Og knows what reason, females with extra fat stores over their pectoral muscles produced more offspring once upon a time and passed on that bizarre mutation that causes chronic back pain and self-loathing in a large percentage of females of the species. No other primate needs it; if it’s “optimal”, wouldn’t other apes have it?
That’s true, but putting the eyes as high as possible on the body makes sense in most environments, if you are going to use the eyes to see danger coming, and to look for desirable things, like food. That even remains true is our crowded cities: the higher your eyes are, the easier it is to see around you in a crowd of other humans. So I don’t think that the position of the eyes and brains can be dismissed as a “legacy feature”.
I didn’t say it was designed. I said that it’s a search. And it doesn’t just find what works - it finds what works best (best defined by reproduction before death etc…) while satisfying multiple and often competing constraints. Your knees are sufficient to run you long distances to find food, a new environment if this one goes to shit and a maiden in waiting to do the deed before you die. (I’m not being wholly inclusive here, just representative).
The answer to the OP is thus very complicated and involves many tradeoffs. But it is not “invalid question.”
Compared to just about everything else, the brain is pretty darned well protected. Predators don’t generally leap at the head – all they’ll get is a mouthful of bone. I’ve seen (ghastly) pictures of a guy whose head was chewed on by a grizzly bear. The damage wasn’t pretty, but it wasn’t to the brain.
Predators go for the throat, legs, and belly. Admittedly, some will also go for the spinal column which might not be so vulnerable if the brain were in a more central location.
Another way of thinking of it is, why not put the brain in the same package as the sensory apparati? If you lose them, it’s game over anyway.
But if you were designed like most of the rest of the mammals you would have around six of them arrayed down your torso.
Or hanging between your legs. :eek:
I’d speculate the proximity of 4 of the 5 sense organs being located so close to the processor has more to do with reducing the length of the data runs than with getting the data there faster. The longer the nerve carrying the info, the more chances there are for damage to it?
How many of us have one or more numb spots on our bodies resulting from injuries?
No, I understand that, and didn’t mean to suggest you did. I guess I’m tripping up on the word “optimal”. Optimal, to me, suggests perfection, which implies, if not design, at least stability and unchangingness. If something is “optimal”, it’s the most perfect form possible out of any imaginable form. I don’t see that as true with…well, with most of anatomy and behavior.
When we get questions along the lines of, “Why would something as maladaptive as homosexuality continue to exist?” or “Why don’t any animals have wheels instead of feet?”, it’s generally pointed out that evolution doesn’t result in the most *perfect *answer, but the one that works for just enough of the individuals within a species to continue that mutation at a slightly greater rate than the individuals without the adaptation.
But I agree with you that we can offer speculation on questions like these, as long as we all understand that “why”, in this context, really means, “what are the benefits that may have lead to greater reproductive ability from…”
Exactly - they’d be more evenly distributed along my center of gravity so I wouldn’t suffer back pain, and they wouldn’t be round and full of fat all the time, they’d only swell slightly when I was lactating.
I can’t begin to imagine how udders would work in an upright position, however!
But you need to add that it only works with what is available to it. Human evolution was constrained to work with the building blocks that were available to our ancestors. There are dozens of better designs for things like the esophagus, eye, and knee, but we’d already gone down an evolutionary path that made it impossible (or extremely unlikely) to end up with them. It’s certainly not “best” if you include designs used by other creatures, let alone other possible designs.
And evolutionary choices aren’t about finding what is “best”. If a change is neutral or not enough detrimental then it may be passed along. Someday down the road it may become a liability but by then it’s not likely that it will be lost.
