There are some interesting observations:

When it comes to software architecture, form follows function. Here we mean "follows" not in the traditional sense of dictating function. Instead, we mean that the distinct identities of the system's architectural elements often don't start to emerge until after the code is working.

One always has, at every stage, in the process, a working system. I find that teams can grow much more complex entities in four months than they can build.

Most interactions in a system tend to be within layers, or between adjacent layers. Individual layers tend to be about things that change at similar rates. Things that change at different rates diverge. Differential rates of change encourage layers to emerge.

Slowly evolving objects are bulwarks against change. They embody the wisdom that the system has accrued in its prior interactions with its environment. Like tenure, tradition, big corporations, and conservative politics, they maintain what has worked. They worked once, so they are kept around. They had a good idea once, so maybe they are a better than even bet to have another one.

The genes / patterns that they identify are good indicators for successful open source projects. There's nothing surprising, but the paper puts a number of things together in one place.