Recent research suggests that hands and feet evolved from fins due to gains in DNA components that activate certain genes.
Researches added extra Hoxd13, a gene known to affect the forming of body parts, to the fin of a zebrafish embryo. The experimental embryo developed more cartilage and had reduced fin cartilage. This is consistent with the formation process of human limbs. As a result, the zebrafish developed one limb that appeared more like a leg than a fin.
After they confirmed that Hoxd13 is essential to limb development, the researches guessed that evolutions in control elements were responsible for increased expression of that gene. They introduced a Hoxd13 control element that is present in mice to the zebrafish. As they suspected, the control element had the ability to drive gene expression in mice.
http://www.sciencedaily.com/releases/2012/12/121210124521.htm
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