Anatomy And Physiology

10 Interesting Facts Human Body Evolution



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The human body is a weird piece of work.  Our ancestors rather quickly evolved from quadrupeds to tree-climbers to true bipeds, and the resultant bodies, those of Homo sapiens, bear the strange marks of this transition.  The following list is comprised of ten of the most interesting and unusual quirks that our evolutionary history has left in us.

1. Reproduction Redux

The human birth canal is, one must admit, a bit of a disaster zone (cue Christopher Hitchens-esque joke about the birth canal being too small and the infant prefrontal cortex being too big, which is bad news  in the long run for those of us who like our birth canals…tight).  Childbirth is agony, and for most of human history, birth has been one of the leading causes of death.  When we look at the rest of the animal kingdom, we find that this is not the case.  Horses, giraffes, sharks, and chicken eggs all just sort of effortlessly drop free of their mothers, who seem to hardly take notice of the event.  We, on the other hand, as often as not find it easier to just cut our offspring out of the mother’s side.  It’s not often thought about, but it is very strange indeed that evolution has done this to us, and the phenomenon begs an explanation.

As it turns out, the simple fact is that humans still have the reproductive tract of a quadruped, which has been bent out of shape to accommodate our newfound upright posture while the hips were simultaneously narrowed.  In concert, these factors cause a veritable symphony of bad news for the various and multifarious acts associated with human procreation.

2. The Appendix in Limbo

Today, the appendix is a useless organ that has a tendency in some individuals to turn into a nasty episode of sickness and surgery.  Before modern surgical techniques, however, the appendix spent millennia as a useless organ that doubled as a ticking time bomb, waiting to literally explode and kill a significant proportion of the people who have ever lived on this planet. 

The story of the appendix is an interesting one indeed.   First, it’s important to note that organs cost lots of energy to build.  Second, keep in mind that the appendix is very useful in herbivores for processing roughage like leaves and stems.  So, when human ancestors made the transition toward eating more meat and fewer vegetables, it was only economic that the size of the appendix should fall.  However, the organ has an opening at its intersection with the intestines, and as the organ shrank, so did this opening.  Eventually, the appendix got small enough that bits of food passing by could clog it, causing it to become infected and swell with appendicitis.  So, now, the organ is caught in evolutionary limbo.  It can’t get smaller, because that would make it even easier to clog, resulting in more cases of appendicitis.  It can’t get bigger, because it doesn’t provide enough extra energy in food processing to properly pay for itself.  So, for the foreseeable evolutionary future, we’re stuck with deadly pseudo-organs in our guts, just waiting for modern medicine to drop its guard so that it can pounce on us once again.

3. Too Many Teeth

Almost all humans have to get their wisdom teeth removed, and many have to use braces to straighten out their fangs during their adolescent years.  Even with these corrections, however, many people still have teeth pointing every which way.  Oddly, if you go to a museum that shows the skeletons of other species or look at most animals in the mouth, you’ll find that their teeth naturally lie in just about the ideal pattern for their particular species.

As it turns out, our ancestors had jaws much heavier and bigger than ours.  As our brains grew, we needed more head space to accommodate it, and the jaws and facial bones were sacrificed, growing much smaller with time.  However, the brain grew so quickly that the jaws had to shrink faster than evolution could make us shed teeth, leaving us with far too little space in our head for the number of teeth that we grow.

4. The Eye Doesn’t See All

You’re probably unaware of it, but each of your eyes has a huge blind spot right in the middle of your field of vision.  People disbelieve it at first, but a very simple series of tests involving the closure of one eye and the focusing of the other on a single point while simultaneously locating a moving object can prove that this is true.  The brain creates a full image of what’s in front of you by constantly scanning the world around you and amalgamating the images to make the blind spots seem to disappear.

This occurrence is caused by the fact that the eye basically evolved backwards.  Because of the way the eye was constructed thousands of millennia ago, many of the blood vessels and nerves in the eye ball pass between the pupil and the light-sensitive cells on the back of the eye, blocking patches of the light that comes through.

5. The Eye REALLY Doesn’t See All

The visible spectrum is such a tiny fraction of all the radiation that exists out there that, if we were observers looking at humanity, the difference between a blind person and a sighted person would be almost negligible.  Most of the information that the universe hurls our way is completely lost on us, and it wasn’t until very recently indeed that we even began to miss it.

6. Your Fun-Bits Ain’t Always so Fun

The proximity of our (and, in fairness, most animals’) genitals to our waste disposal apparatus has long been a source of humor among scientists wishing to make fun of the intelligent design movement.  After all, as the joke goes, we basically have a theme park running through a waste treatment facility.  The fact that these two tracts share a single point of contact with the outside world probably hearkens back to the old, old days in which organisms were first starting to get holes.  This trend started with one exterior passageway, and anything you needed an orifice for, that solitary hole was there to do.

7.  One Hole Too Few…

Speaking of holes that are forced into serving double-duty, it seems dangerously stupid that we eat and breathe through the same opening.  This design flaw is really the only reason that people ever choke to death.  And it would be relatively easy to fix this problem, too.  After all, as Neil DeGrasse Tyson once pointed out, we’re not far removed from whales, and they most definitely do not eat where they breathe. 

8.  Getting “Stung” by Hypodermic Needles Sucks

When you’re a tree-dwelling primate, your biggest concerns as far as dangerous animals goes are poisonous insects and deadly snakes that live in the trees you inhabit.  Tiny pinpricks, while not badly painful, are deeply disturbing, as they replicate the feeling of a stinger or a fang being pressed into the body…

…and that is precisely why getting a shot is a disproportionately unpleasant experience.  We go to a doctor, wait an hour, and then get pricked with what feels like the stingers  of our ancestors’ most deadly adversaries.  Not a day at the beach, unless of course the beach in question is covered in scorpions. 

9. Posthensile Toes

We tend to think of prehensile digits as the pinnacle of evolution, what with our big talk about our opposable thumbs.  But in reality, we’re actually down a pair of thumbs from our ancestors, whose feet looked just like their hands.  Our digits are becoming less opposable as time passes, and we just won’t stop talking about how important these thumb things are to the development of civilization.

Of course, our big toes lost their prehensile traits, and entered the world of the “posthensile,” in the name of achieving balance in bipedal walking.  It wouldn’t do to have a toe-thumb off to the side of the rest of the toes, not carrying its weight when it comes to keeping a biped upright just to preserve the ability to pick up shiny things and bang rocks with sticks a little bit more easily.

10. The Body Is Here Today

It is astonishingly improbable that humanity has survived as long as it has.  We were forced out of our trees, out onto the savannah with the lions and leopards, and in a brand new environment to which we were ill-adapted, we simply evolved around the problem.  We made massive evolutionary changes in a tiny amount of time.  99 species out of 100 would have gone extinct in the conditions humanity faced, and we did, in fact, on several occasions become as endangered as mammals can get and still be able come back from it. 

We pay for this with lousy childbirth, chronically painful and stiff backs, brains big enough to make us acutely aware of impending death, fear of things like needles because we so recently lived in a different world, teeth that can maim and kill us from the inside, and an entire organ dedicated to exploding inside of you along with a large dose of poison.  But, somehow, we’re here. 

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ARTICLE SOURCES AND CITATIONS
  • InfoBoxCallToAction ActionArrowhttp://en.wikipedia.org/wiki/Human_reproduction
  • InfoBoxCallToAction ActionArrowhttp://en.wikipedia.org/wiki/Vermiform_appendix
  • InfoBoxCallToAction ActionArrowhttp://en.wikipedia.org/wiki/Human_tooth
  • InfoBoxCallToAction ActionArrowhttp://www.youtube.com/watch?v=yB8pVtC73Kc
  • InfoBoxCallToAction ActionArrowhttp://en.wikipedia.org/wiki/Prehensile_feet
  • InfoBoxCallToAction ActionArrowhttp://www.dailygalaxy.com/my_weblog/2009/06/was-the-human-species-almost-extinct-70000-years-ago.html