Chordates may have started with this little eel-like critter, known as Pikaia, but today spans a diverse range of animals, such as mammals, birds, and fish. In a surprising discovery, a group of researchers have found that some of the signalling machinery used by chordates dates far further back.
Chordates use a signal molecule called retinoic acid (RA) to construct their bodies during development. Since RA seemed to be restricted to chordates, it was assumed to have arisen relatively recently, in conjunction with the origin of chordates. In an article published in the scientific journal Evolution & Development, a group of researchers have discovered pieces of the "RA genetic machinery" in a sea-urchin, pushing its origin back in evolutionary time. When more species have their genomes sequenced, the machinery may in fact turn out to be even older. As the authors note, it is possible that the parts of the RA machinery had a different function in its early ancestor, handling another signal molecule than retinoic acid.
This illustrates an important point about front-loading. A designer wanting to front-load the evolution of life need not have inserted useless genes for eyes and hearts in a unicellular organism, where mutations would erase them in a few million years. Instead, the designer could have designed genes that could be adapted to multiple functions, so that a gene could serve one function in a unicellular organism and another in a multicellular organism. Flexibility – not micro-managing – is the key.
CaÃ±estro C., et al., "Is retinoic acid genetic machinery a chordate innovation?", Evolution & Development 8(5):394-406 (2006)