Do Birds Have Thumbs?

Posted by : Unknown 1 oct 2011

Biologists have been trying to fathom whether the innermost digit of a bird's three-pronged wing acts like a thumb or an index finger.

The innermost digit of a bird's three-pronged wing isn't a thumb, or a finger, but a bit of both.
The study, carried out on chicken chicks, uncovered a new mystery: a lack of correspondence, or homology, between the other two digits buried in the bird wing and those found in the foot.

Researchers have shown that the first digits of chick wings and feet both arise from the same genetic coding, but that, in the wing, the digit develops from the position in the embryo normally reserved for the index.

It is the kind of question that keeps biologists up at night: from an evolutionary standpoint, is the innermost digit of a bird's three-pronged wing more like a thumb or an index finger?
A study published online Sunday by Nature says it's a bit of both.
The stem cells in birds that normally produce the first digit die off during early stages of embryonic development, it found, while cells programmed to manufacture the index unit give rise instead to a thumb-like appendage.
Member No. 2, in other words, has undergone a shift in digital identity.
All four-legged animals with backbones -- vertebrates -- share an ancient template of five digits per limb. But that has not kept evolution from generating a numerically diverse menagerie for grasping, clawing and walking.