The human race's prospects of survival were considerably better when we were defenceless against tigers than they are today when we have become defenceless against ourselves.

Toynbee contrasts early humanity’s vulnerability to external natural threats with modern humanity’s vulnerability to self-inflicted dangers. The image of being “defenceless against tigers” evokes a world in which survival depended on confronting forces outside ourselves; by comparison, being “defenceless against ourselves” points to the moral, political, and technological capacities that can turn inward—war, ideological fanaticism, environmental destruction, or weapons of mass annihilation. The quote reflects a twentieth-century historical sensibility: progress in power does not guarantee progress in wisdom. Toynbee’s larger civilizational theme—decline through failures of response—appears here as a warning that the gravest threats arise when human ingenuity outpaces self-restraint.