Do Birds Have Thumbs?

Have you ever wondered if birds have wing thumbs under their feathers? Because of conflicting evidence, debate has flourished for more than a century as to whether the three-part bone structure of a bird wing corresponds to the thumb, index and middle finger, or to the index, middle and ring fingers.

Working with chickens, researchers from Yale University led by Dr Gunter Wagner used a technique called gene expression profiling to solve the digital mystery. The new study published online in the journal Nature says the innermost digit of a bird's three-pronged wing acts a little like both a thumb and an index finger.

While still in the egg, scientists found the stemcells of bird embryos that normally produce the first digit die off during early stages of development, and the cells programmed to manufacture the index unit give rise instead to a thumb-like appendage.

Human and primate hands and feet have five fingers or toes each; birds have three in their wings and two, three or four digits on their feet.

Sources: 

Nature Weekly Journal of International Science: Transcriptomic analysis of avian digits reveals conservedand derived digit identities in birds 

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Related Article: What are Some Differences in Birds' Feet?: http://bit.ly/q2i09D