The hypothesis of formative causation predicts that as animals of a given species learn a new pattern of behaviour, other similar animals will subsequently tend to learn the same thing more readily all over the world, as a result of a process called morphic resonance. The more that learn it, the easier it should become for others. This possibility was tested with day- old chicks using a simple learned response, a conditioned aversion. The test took place in the laboratory of Steven Rose, a sceptic, following a standard procedure used routinely in his laboratory, and was carried out blind by a summer student who knew nothing of the purpose of the experiment nor of morphic resonance. The chicks were exposed either to a test stimulus, a small yellow light-emitting diode (LED), or a control stimulus, a chrome bead. Half an hour after pecking the stimulus, the control chicks received an injection of saline solution, and the test chicks an injection of lithium chloride, which made them mildly sick. They were then tested three hours later, each chick being exposed sequentially to the control and the test stimulus, when most test birds were averse to pecking the yellow LED, but not averse to pecking the control bead. The response of the chicks was measured by recording the latency, the time delay in seconds before they first pecked the stimulus. The same experimental procedure was repeated for 37 days. If morphic resonance were occurring, successive batches of chicks should have shown an increasing aversion to the yellow LED, even in the initial training procedure, by morphic resonance from their averse predecessors. The controls should have shown no such increasing aversion. I think the results are consistent with such an effect, which shows up with a high degree of statistical significance (p < 0.01) when the aversion to the yellow bead is measured relative to the control. Rose disagrees with this interpretation.