why do we have 2 bones in the forearm and only one in the upper arm?
wouldn't it be forward evolution for us to have only one bone in the forearm, as with the humerus? What advantage does a double bone structure offer? For example, the tibia and the ulna of the horse are highly reduced structures.
- secretsauceLv 71 decade agoFavorite Answer
The two bones are what allow us to rotate the wrist laterally.
To see what I mean,
1. Hold out your right arm in front of you with your thumb pointed up (12:00 position).
2. With your left hand grab your right arm just above the elbow.
3. Notice that you have no trouble rotating your wrist so that your thumb is pointing to the left (9:00 position). You can do this without any rotation of the upper arm at all.
You would not be able to do that if you just had one forarm bone locked at the elbow. You could bend your arm at the elbow, but not rotate your wrist in that way.
To feel the two forearm bones rotating around each other, grab your forearm with your left hand while you rotate the wrist.
- 1 decade ago
Not only does the combination of the two bones provide flexiblity in the wrist....think about what would happen if you only had ONE bone in your forearm and it SNAPPED?
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- Anonymous1 decade ago
The two bone system allows us to twist our hands, because they curl around themselves forming an "X", and make our hand face the other way: A single bone wouldnt be able to do that. This is useful for climbing trees, and now is useful for handling tools.
- MarissaLv 44 years ago
What about the weenis (it's like the kneecap of your elbow)? Maybe J.K. Rowling's not an anatomist. Or she may be not-a-mathematician. In fact, she could be both a not-anatomist and a not-mathematician.
- DAR76Lv 71 decade ago
you also have to remember that the humerus is bigger and thicker than the ulna and radius. It provide more flexibility at the wrist.
- 1 decade ago
i think it has to do with the additional range of motion at the wrist.