Species go extinct because there are historical contraints built into a given body or a given design.

Kelly’s remark frames extinction not simply as “bad luck” or external catastrophe, but as a consequence of path dependence in evolution. Organisms inherit architectures—body plans, developmental pathways, and trade-offs—that make some adaptations easy and others effectively unreachable. When environments shift, a lineage may be unable to reconfigure itself fast enough or in the needed direction because its prior evolutionary commitments constrain what can be changed without breaking the whole system. The quote echoes a common evolutionary idea: history matters, and design is never from scratch; it is modification of what already exists. Extinction, in this view, is often the price of being locked into an earlier solution.