Peter and Moses: Chimpanzees Who Write
THE WISH TO design and erect a Mental Ladder, one that arranged animal species by their intelligence, followed by half a century the understanding of how to build such a ladder based on structure. Darwin's initial understanding of the evolution of the physical aspects of species set in motion the building of a metaphorical ladder of structure, a hierarchy of species based on physical traits.
Although Darwin clearly believed that a like-constructed Mental Ladder was feasible--his 1872 book on emotions makes this evident--the attempt to build one was surprisingly slow in coming. While naturalists rushed to find the similarities and differences among animals in order to identify genera and ancestral relationships, attempts to make such comparisons for mental activity were scarce. The lack of a fossil record for mentality might be a chief reason, but so might the fact that human beings regard mental activity as more mystical, and less measurable, than bones and their structure.
The Ladder of Mental Life comprises different degrees of development of animal life represented by the rungs. The upright poles form the scaffold that holds the rungs in place from top and bottom, from, say, amoebae to ourselves. The idea originated with Aristotle and was rejuvenated and diagrammed by the Victorians, most likely because Darwinism gave the idea of the Mental Ladder a certain prominence and respectability. Romanes, writing in 1882, tried to meld the newly formed principles of evolution into a social philosophy, and offered a ladder of mental abilities of species and genera and the emotional potentials of humankind. His ladder is re-created in Figures 8.1, 8.2, and 8.3. These figures display, in a way that mere words cannot, the goal and attributes of the late Victorian Mental Ladder.
The proposed ladder of intellectual development starts with the lower rungs representing protoplasmic movements (performed by protoplasmic organisms, such as paramecia and amoebae), "rises" through various levels of neural activity, and reaches memory with the echinoderms. Higher organisms are capable of instinct, association, recognition, rea-