<div class="abstract" data-abstract-type="normal"><p>This article critically examines the insights that biology (including evolutionary analysis and neuroscience data) offers for understanding the relationship between family law and family stability. The paper initially considers evolutionary analysis, comparative anatomy, and neuroscience data to conclude that while the pair bond appears to be a universal feature of human societies, long-term fidelity is not. The second part of the paper considers the benefits and limitations of evolutionary analysis concluding, first, that evolutionary analysis, without connection to modern neuroscience or sociological data, remains highly speculative; second, that where the evolutionary analysis is borne out by modern neuroscience and/or sociological data, it is more persuasive, but often leads to obvious conclusions; and third, that undertaking this type of examination nonetheless leads to new insights or new questions that should prompt productive research.</p></div>