The effect of biological and environmental factors on human behavior is introduced through the turtle analogy but is primarily developed through Sapolsky’s system of contesting the concepts of free will and moral judgment. The system utilizes a time-based approach to illustrate that there is “no room” for free will in our understanding of behavior. Biological forces include a person’s biological states and their genetics. While many people assume there is a stark divide between biology and environment, Sapolsky argues that that is not the case. The environment, for instance, significantly affects the development of the prefrontal cortex, and genes can be turned on and off by environmental factors, referred to as epigenetic changes.

The idea that environmental factors contribute to antisocial behavior is exemplified through the Adverse Childhood Experiences (ACE) score. Adverse experiences are divided into 10 categories: physical, emotional, or sexual abuse; physical or emotional neglect; mental illness; incarceration; substance abuse; divorce within the family; or having a mother who is physically abused. Each lived type of experience is included in a person’s score, with a highest possible score of 10. The ACE score is directly correlated with antisocial behavior: “For every step higher in one’s ACE score, there is roughly a 35 percent increase in the likelihood of adult antisocial behavior” (66).