Whitehead, Modes of Thought, Nature Alive,

in the higher mammals and more particularly in mankind, we have clear evidence of mentality habitually effective. In our own experience, our knowledge consciously entertained and systematized can only mean such mentality, directly observed.
The qualities entertained as objects in conceptual activity are of the nature of catalytic agents, in the sense in which that phrase is used in chemistry. They modify the aesthetic process by which the occasion constitutes itself out of the many streams of feeling received from the past. Whitehead, Modes of Thought, Nature Alive, p. 168

Examine the relation of this claim about the role of mentality to Whiteheads other claim that the characteristics of life are absolute self-enjoyment, creative activity, aim (ibid., p. 152).