Which of the following best describes our current understanding of the causal relationships between physiology, anatomy and behavior in humans?
1) Physiology and anatomy have a direct causal relationship with behavior in humans.
2) Physiology and anatomy have an indirect causal relationship with behavior in humans.
3) Physiology and anatomy have no causal relationship with behavior in humans.
4) The causal relationships between physiology, anatomy, and behavior in humans are not yet fully understood.