How was the USA's Cambridge-Boston biotech hub built?

While there are several commonly-cited reasons for the present pre-eminence of the Cambridge-Boston. USA, biotech cluster, it's clear that the hub is greater than the sum of its parts.

According to one estimate, the main hub in Cambridge contains firms that have attracted over $14 billion in investments from venture-capitalists.

And while the area plays host to an array of biomedical firms, both very small and very large, a cornucopia of suppliers, contract research organizations, investors, lawyers and others have also been built up to support them.