The Expanding Circle: Ethics and Sociobiology

Overview
Peter Singer develops a wide-ranging account of how moral concern has widened from immediate kin networks to encompass distant strangers and nonhuman animals. He uses the metaphor of an "expanding circle" to describe moral progress, arguing that empathy and reason together can push the boundaries of moral regard outward. The book brings philosophical analysis into dialogue with the findings of evolutionary biology and sociobiology, testing whether scientific accounts of human origins undermine or support moral universalism.

Central Argument
Singer contends that our moral intuitions have evolutionary roots but are not strictly determined by them. Biological predispositions such as altruism toward kin and reciprocity within groups helped human survival, yet reason enables critique and extension of these predispositions. He insists that the capacity for impartial moral reasoning, treating like cases alike, favors widening the circle of concern to include all who can suffer or have interests, rather than limiting obligations to kin, tribe, or species.

Engagement with Sociobiology
The book carefully engages with sociobiological explanations that link moral behavior to genetic self-interest and group selection. Singer acknowledges that evolutionary theory can illuminate why particular moral feelings exist, but he warns against deriving "ought" from "is." Biological origins may explain tendencies, yet they cannot by themselves justify ethical norms. He challenges reductionist readings that claim genetics fully determines moral obligation, arguing that reflective principles can override narrow evolutionary impulses.

Moral Expansion and Mechanisms
Singer explores psychological and social mechanisms that enable moral expansion: empathy, imaginative perspective-taking, rational argument, and institutional change. Empathy fosters identification with others, while reason discerns inconsistencies in privileging some beings over equally relevant others. Public debate, philosophical reflection, and changes in law and custom further institutionalize broader obligations. The expanding circle proceeds unevenly and faces resistance from tribal loyalties and parochial biases, but historical examples show substantial moral widening over time.

Normative Implications
The argument culminates in normative commitments that resonate with utilitarian impartiality: equal consideration of interests and moral regard for all who can suffer. Singer presses these commitments toward controversial conclusions, including strong critiques of speciesism and calls to extend ethical concern to many nonhuman animals. He also draws out implications for issues such as racism, sexism, and international obligations, arguing that truly universal ethics demands transcending arbitrary boundaries and giving weight to interests regardless of proximity or membership.

Legacy and Significance
The book situates ethical progress within a naturalistic framework without surrendering normative standards to biology. Its synthesis of philosophical argument and engagement with scientific accounts influenced debates about moral realism, animal ethics, and the philosophical significance of evolutionary explanations. By framing moral development as an expandable circle guided by reason and compassion, Singer offers a provocative, aspirational vision of how ethical life can continue to broaden and deepen.