The present research used archaeological data, i.e., the data obtained from kamekan jar burials in the Mikuni Hills of the northern Kyushu area in the Middle Yayoi period, to test the parochial altruism model. This model argued that out-group hate and in-group favor coevolved via prehistoric intergroup conflicts. If this model is accurate, such an out-group hate and in-group favor could be reflected in the archaeological remains, such as pottery making; the more frequent intergroup conflicts are and the more each group is opposed, the more independent and coherent each group will be and more evident cultural identity could be established within each group. We employed an elliptic Fourier analysis for the shapes of kamekan jar burials. We examined whether frequent intergroup conflicts in the period influenced kamekan jar pottery between subareas of the Mikuni Hills. The results suggested that the shapes of kamekan jar burials after the KIIIa type are slightly different between subareas, which is partially consistent with the model. However, the results do not support the model directly.