Crack propagation in slow motion

On my first positional inheritance page, I used an illustration of a lighting strike in slow motion - as an illustration of the concept.

Here's a similar video of glass breaking in slow motion:

The video illustrates that cracks propagate from locations other than the branching tips. Some distance behind the tip of the crack is still a possible source of new (usually transverse) cracks. In a Darwinian model of splitting and recombining individuals, the entities that are evolving are crack tips - but this video illustrates that the notion of a crack tip has to be significantly extended in space if it is to result in a good quality model.

The resulting shatter pattern appears to be fairly heavily reticulated. It looks like a network - rather than a simple tree. However, appearances can be deceptive. If you look at the slow motion evolution, each crack forms from an existing crack - and there's a strict parent-offspring relationship that holds everywhere. In this case, the pattern of cracks forms a genuine family tree - something you might not guess at if looking at the resulting static fracture pattern.