Researchers solve mystery of disappearing bird digit

September 4, 2011
A genomic analysis shows that precursor cells pb that form index finger in five-fingered vertebrates can form the "thumb" (in orange) or first digit in three-digit bird wing Credit: courtesy Yale University

Evolution adds and subtracts, and nowhere is this math more evident than in vertebrates, which are programmed to have five digits on each limb. But many species do not. Snakes, of course, have no digits, and birds have three.

Yale scientists now have a good handle on how these are orchestrated in the embryo, but there is still one outstanding debate on birds: Which digits are they: a thumb with index and middle fingers, or the index, middle and ?

In five-digit vertebrates, the thumb comes from the precursor stem cells labeled pa. While birds have a digit that looks like a thumb, pa precursor cells die off during development and never produce a digit in adults. As a result, scientists have wondered whether in pb can make a thumb.

Yale scientists have completed a of birds that reveals the answer (shown in orange on illustration). It is a hands down "yes" — even though the first bird digit develops where the index finger on a five-finger vertebrae should be.

The results are published online Sept. 4 in the journal Nature.

Explore further: Scientists develop 'clever' artificial hand

Related Stories

Scientists develop 'clever' artificial hand

September 7, 2005

Scientists have developed a new ultra-light limb that can mimic the movement in a real hand better than any currently available. This research was presented today at the Institute of Physics conference Sensors and their Applications ...

High-tech bionic hand invented in England

July 19, 2007

The new, high-tech i-LIMB bionic hand, with five motorized fingers, will soon be sold in Britain for about $17,000, The Telegraph reported Thursday.

Researchers describe how digits grow

March 11, 2008

Researchers at the University of Wisconsin School of Medicine and Public Health (SMPH) are wagging a finger at currently held notions about the way digits are formed.

How the mole got its 12 fingers

July 14, 2011

Polydactyly is a hereditary anomaly that is relatively common in both humans and animals. Moles also have additional fingers. In their case, however, the irregularity compared to the five-finger formula of land vertebrates ...

Recommended for you

Study finds 'rudimentary' empathy in macaques

December 1, 2015

(—A pair of researchers with Centre National de la Recherche Scientifique and Université Lyon, in France has conducted a study that has shown that macaques have at least some degree of empathy towards their fellow ...

Scientists overcome key CRISPR-Cas9 genome editing hurdle

December 1, 2015

Researchers at the Broad Institute of MIT and Harvard and the McGovern Institute for Brain Research at MIT have engineered changes to the revolutionary CRISPR-Cas9 genome editing system that significantly cut down on "off-target" ...

Which came first—the sponge or the comb jelly?

December 1, 2015

Bristol study reaffirms classical view of early animal evolution. Whether sponges or comb jellies (also known as sea gooseberries) represent the oldest extant animal phylum is of crucial importance to our understanding of ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (1) Sep 04, 2011
Now if they could just figure out what happened to the missing Simpson's finger.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.