Complexity is easy to admire and hard to explain. A protein, a living cell, a piece of technology, even a culture can be described by structure, matter, energy, or information, but that still misses the most revealing feature: each one carries a history of successful construction. We dig into assembly theory and its core idea that complex things embody “how they got built,” captured by the assembly index as a measure of historical depth. Then we push on the question assembly theory leaves ha...