Source: Rept0n1x (CC-BY-SA-3.0). Power line in Cheshire (image available here). (e) Biology  Given their cellular structures, ABMs have found a wide range of biological and medical applications. In biology, an area which was ripe for ABMs was so-called morphogenesis - the biological process that causes  7 8 9  For the taxi example, see Seow and Lee (2010). For example, Pechoucek and Sislak (2009). See Fagnant and Kockelman (2014). 16  All speeches are available online at www.bankofengland.co.uk/publications/Pages/speeches/default.aspx  16  an organism to develop shape and pattern. In 1953, Alan Turing had considered this when explaining the origins of the “dappled” pattern found on Friesian cattle. Biologists began thinking about constructing an ABM of an entire cell from the late 1990s (Tomita et al (1999)). In more recent years, ABMs have broken into the biomedical sciences, being applied to cancer, immunology, vascular disease and in vitro development (Thorne et al (2007)). One of the most exciting recent developments in ABMs has been the construction of a complete model of the human pathogen Mycoplasma genitalium (Karr et al (2012)). These models are likely to become more popular with the advent of powerful gene editing technologies. Most recently, ABMs has been to streamline drug or device design, simulate clinical trials and predict the effects of drugs on individuals. ABMs can help bridge the different scales inherent in biological problems – from gene to cell, from cell to tissue, and from tissue to organism.

Looking at these patterns over time paints a somewhat more optimistic picture (Chart 4). There is clear evidence of economics having become more cross-disciplinary during the course of this century. Once finance is taken out of these estimates, however, economics continues to lag. And alternative metrics, such as the degree of rigidity in hierarchies and gender diversity, paint economics in a less favourable light (Fourcade, Ollion and Algan (2015)). Despite progress, it is difficult to escape the conclusion that economics remains an insular, self-referential discipline. 9  All speeches are available online at www.bankofengland.co.uk/publications/Pages/speeches/default.aspx  9  The economics profession’s intellectual bloodline is purer than in most other disciplines. In some respects, it is a source of strength that the workhorse economic model is a thoroughbred. That quest for purity also contributed importantly, however, to this workhorse falling at the first meaningful fence put in its path. This suggests it is probably as good a time as any to consider mixing the intellectual bloodline, just as physics and other of the natural sciences have done. Agent-Based Models (ABMs)  Against this backdrop, what other disciplines and approaches might be productive alternative lines of enquiry? One potentially promising strand is so-called agent-based modelling. Agent-based models (ABMs) are interconnected systems of individual “agents” who follow well-defined behavioural rules of thumb. What makes these models interesting is that these agents are heterogeneous and interactive. In other words, these models relax one of the key assumptions of the standard model – a single, representative agent.