Heya all. Here’s one of these thoughts you can only ponder late at night while unable to sleep.
Human body (and not only human, but we’ll leave that out) seems to exhibit lateral symmetry. I mean, we’ve got two legs, two feet, two ears, eyes and whatnot, and the left side of the torso looks pretty much like the right side, save for little details like bodily hair distribution. Yet on the inside, the symmetry is only partial! There’s no counterpart to the heart on the right side, the liver is not symmetric, intestines are a mess and so on.
So my question is… Why this inconsistent design? At some point during embryonic development we’re all symmetric, right? Then the fetus somehow starts distinguishing sides. Weird, if you ask me…
Keep in mind that most of your insides are symmetric, except for the organs. The evolutionary advantage of lateral symmetry is that you only need one copy of the genes to build two copies of the structure.
Apparently, the disadvantages of asymmetry in the organs are outweighed by the advantages of their shape.
Hijack - sorry, no answer here, but this is a common misconception. The heart is not on the left side of the body, what you’re feeling is the pumping of blood through one of the vessels located in that area. The heart is in the middle, though tilted slightly, such that it’s probably about 2/3 on the left side and 1/3 on the right.
It seems to me that this internal arrangement is just what you would expect if you consider the grocery bag analogy. Looks good on the outside, but inside the bread is on the left, the cabbage at the bottom, frozen waffles on the other side… in other words, just the happenstance of a long chain of events that lead up to living organisms. Of course here I am getting dangerously close to “the grocery boy made it so”, so perhaps a bad analogy.
Upon reflection I note that where we have two of something - kidneys, ovaries, lungs, etc. they exibit bilateral symmetry. Best was to keep us from tipping over when we walk, I suppose. If we had two stomachs, I don’t doubt they’d be placed on either side of the abdomen. But seeing ad how we have 1 stomach and 1 liver, the current placement is the best arrangment to keep our center of gravity where it’s easy to deal with.
Alright, God didn’t make it so. [The forces of] Nature made it so.
Yes there are, and there was a recent article in Scientific American, I think, that discussed how this reversed arrangement also seems to involve a whole set of health problems.
At the risk of sounding like a broken record, I addressed the issue of symmetry in this thread. I repeat the relevant part regarding our innards here:
Also, realize that the heart begins as two independent pumps which later fuse. Thus, you have one organ which began as essentially two, and which still operates largely as two.
I would guess that their assymmetrical features evolved on top of generally symmetrical body plans, for fighting, attracting mates, or what have you. In the case of humans, I would hypothesize that our ancestors had symmetrical guts, but that assymmetrical guts evolved because longer intestines provide more time and space for nutrients to be absorbed.
As a side note, it seems that our concept of directions (left/right, forward/backward) is a direct result of our bilateral symmetry. Imagine what our sense of direction would be like if we were radially symmetric, like jellyfish. I would even venture to suggest that our eagerness to divide things into groups of two (black/white, yes/no, friend/enemy) is linked to out bilateral symmetry. How many major political parties do you think we’d have in the US if we all looked like sea urchins?
In a recent thread - might be the one linked to above; I’m too lazy to check - it was pointed out that our symmetrical and asymmetrical features arise from different embryonic cell layers.
I’m no biologist, but isn’t that a little like saying “The meal was wonderful, except for the food.” I mean, aren’t “insides” and “organs” essentially the same thing? Or did I miss something?
