Kirschner, HMS professor and chair of the Dept. of Systems Biology, and Gerhart show that newly discovered molecular properties of organisms facilitate evolution.

The origin of novelty, the development of new arrangements of interlocking parts that some call "irreducibly complex," can only be understood in the light of the last 20 years of research in cell biology and development.

We now know that the 'parts' that make up a living organism are very unlike the rigid parts designed for machines. Instead, they can flexibly connect and re-connect, using the same pieces over and over to make new functions.

For example, one might think that a mutation that makes the neck of a giraffe longer would have to be accompanied by several other mutations, one that expands the length of the muscles of the neck, another that makes the blood vessels longer, and so on. But instead, the muscles grow to fit the length of the bone and the blood vessels grow until all the muscles have a sufficient supply of oxygen. Apparently very complex adaptations can therefore be achieved with few, simple mutations.

Today, it is understood for the first time that all animals use the same set of core processes to develop into adult forms. Applying this knowledge to evolution, the authors show that novel traits emerge from the ways the organism is constructed: its complex mechanisms for adapting to the environment, its modular construction, and its internal circuitry that can be re-specified and reconnected.

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