This volume is perhaps best characterized by its interdisciplinary nature and reliance on an eclectic range of approaches. One theme that naturally emerges from the collected essays is that of causation versus analogy. Phenomena defined at multiple levels can in principle be studied in two ways - vertically and horizontally. The vertical strategy directly specifies causal relations holding between levels, whereas the horizontal approach looks for parallels between levels, seeking to isolate shared causal properties. One of the essays here stands directly for the vertical strategy, while another warns explicitly against the perils of a loose selectionist analogy among levels. Other parallels between evolution and culture are probed, calling attention to the general limits of analogy, or carefully noting the respects in which the proposed analogy is expected to break down. The other themes of economics, optimization, and stability, when not explicitly mentioned, lurk in the background of any treatment of culture and behaviour in relation to natural selection.