  The capacity to resist attacks from the environment is crucial to the
survival of all organisms. We quantitatively analyze the susceptibility of
protein interaction networks of numerous organisms to random and malicious
attacks. We find for all organisms studied that random rewiring improves
protein network robustness, so that actual networks are more fragile than
rewired surrogates. This unexpected fragility contrasts with the behavior of
networks such as the Internet, whose robustness decreases with random rewiring.
We trace this surprising effect to the modular structure of protein networks.
