An innocent form of emergence-what I call "weak emergence"-is now a commonplace in a thriving interdisciplinary nexus of scientific activitysometimes called the "sciences of complexity"-that include connectionist modelling, non-linear dynamics (popularly known as "chaos" theory), and artificial life. 1 After defining it, illustrating it in two contexts, and reviewing the available evidence, I conclude that the scientific and philosophical prospects for weak emergence are bright.Emergence is a tantalizing topic because examples of apparent emergent phenomena abound. Some involve inanimate matter; e.g., a tornado is a selforganizing entity caught up in a global pattern of behavior that seems to be autonomous with respect to the massive aggregation of air and water molecules which constitute it. Another source of examples is the mind; our mental life consist of an autonomous, coherent flow of mental states (beliefs, desires, etc.) that presumably somehow ultimately arise out of the swarm of biochemical activity among our brain's neurons. Life is a third rich source of apparent emergence. For example, the hierarchy of life embraces ecosystems composed of organisms, which are composed of organs, which are composed of cells, which are composed of molecules, but each level in this hierarchy exhibits behavior that seems autonomous with respect to the behavior found at the level below.These examples highlight two admittedly vague but nevertheless useful hallmarks of emergent phenomena:(1) Emergent phenomena are somehow constituted by, and generated from, underlying processes. (2) Emergent phenomena are somehow autonomous from underlying processes.If we place these hallmarks against a backdrop of abundant apparently emergent phenomena, it is clear why emergence is a perennial philosophical puzzle. At worst, the two hallmarks seem to make emergent phenomena flat-out inconsis-

No abstract

This article lists fourteen open problems in artificial life, each of which is a grand challenge requiring a major advance on a fundamental issue for its solution. Each problem is briefly explained, and, where deemed helpful, some promising paths to its solution are indicated.

The web of relations linking technological innovation can be fairly described in terms of patent citations. The resulting patent citation network provides a picture of the large-scale organization of innovations and its time evolution. Here we study the patterns of change of patents registered by the U.S. Patent and Trademark Office. We show that the scaling behavior exhibited by this network is consistent with a preferential attachment mechanism together with a Weibull-shaped aging term. Such an attachment kernel is shared by scientific citation networks, thus indicating a universal type of mechanism linking ideas and designs and their evolution. The implications for evolutionary theory of innovation are discussed.