The 15 properties of life were, I believe, his attempt to find the universal rules underlying the design patterns he described in A Pattern Language. I've long thought that most of those properties could be described algorithmically and was curious what sort of system they would converge to. I suppose nature is one easy answer, but it's not a very useful one.
For those who are interested, there's a nice summary of the properties and analysis of how they relate to each other at http://web.sfc.keio.ac.jp/~iba/papers/PURPLSOC14_Properties.... and a more architecturally-focused take at https://www.archdaily.com/626429/unified-architectural-theor....
He believed that a meadow with a river bend, an old willow tree and a rock to sit on below it was not a scene composed of living and non-living entities, but rather the arrangement of these entities (both internally alive and not) gave rise to a wholistic quantity of life in that space. Depending on where the rock was placed the space itself was more or less alive.
It sounds like a far out, "new agey" idea but I think he argued quite rationally that this framing of life makes far more sense than a binary determination based upon near arbitrary delineations such as sex, reproduction and consumption of resources.
I think he really was onto something personally.
Following this, he published a paper on “harmony-seeking computation” as an approach to optimize “wholeness.” He identified 15 elements of wholeness in designs that might be measured, like the presence of coherent centers, strong boundaries, local symmetries or roughness/imperfection. He proposes that “the harmony that is sought in these computations is indeed what we otherwise call ‘beauty’. But the result of harmony-seeking computations are not merely pretty or artistic. In most cases, they are also better functionally and technically.”
Alexander, Christopher "Harmony-Seeking Computations." International Journal of Unconventional Computing 4 (2008).