I’ve mentioned in a few threads that there’s no part of my body that’s symmetrical. Even my fingers and toes don’t match. Eyes, ears, teeth, nothing matches. Even my nose is slightly off-center. What I’m wondering is: How early in fetal development is this asymmetry established? What could cause it, and am I correct in assuming that it has to happen fairly early, to affect the entire body?
Bilateral symmetry starts developing as early as the blastocyte stage, 5 days after fertilization in humans, with detectable changes in biochemistry.
The formation of the primitive streak at about 14 days post fertilization in humans, marks the first observable structural symmetry.
Development of fingers, toes, and pretty much any recognizable body part comes later.
So at what point does something go “wrong,” and the entire body becomes somewhat asymmetrical?
Maybe your two halves were formed from fetal twins who merged in utero. :eek:
panache45, everybody is somewhat asymmetrical; in most people it’s most noticeable on the inside (heart, liver, most of the digestive tract, etc.), but nobody is perfectly symmetrical. People grow more facial hair on one side than the other. One side is stronger, one more dexterous, one more coordinated: they may all be the same or not. Rings which go on the ring finger in one hand go on the middle in the other. I’ve been fascinated by people’s features since forever: most people have asymmetrical eyes, eyebrows, noses, mouths. A great deal of the purpose of makeup and grooming (hairdos, shaving, plucking) is to enhance symmetry. Are you more asymmetrical than most or “merely”, being an artist, more observant of your asymmetry?
The basic intrinsic asymmetry of the human body (position of heart, liver, spleen etc) starts early during embryonal development and seems to depend on the proper function of cilia, slender motile cell protuberances that help to move extracellular fluid around.
Genetic defects are the cause of situs inversus, in which the major visceral organs are reversed or mirrored from their normal positions.
Minor irregularities, such as slight differences in face, hands , pigmentation and so on do not have a clearly identifiable cause. The processes which shape our bodies during embryonal development do not strictly determine the positions of each cell, they are more like instructions to cells to “keep dividing until the concentration of a extracellular signal substance drops below a certain threshold”, and are therefore subject to random changes in the environment.
No, I really am more asymmetrical than most. I once took a photo of my face, and copied/pasted both sides, so I had a composite “left” face and a composite “right” face. They really did look like two completely different people.