At root is the issue of just what constitutes "proprietary trading" by Banks, especially as it relates to the issue of making trades in securities on behalf of their customers.
According to this line of thought, the verbal abilities that blossom in the two year old allow events to be coded in a form radically different from the action-based codes of the infant.
Their underlying reason for disputing this theory is that, in their studies of human evolution, they have encountered other primates, man's closest, hairiest relatives, who have longer fourth fingers.