Debunking the Plaintiffs’ Reptile Theory: Why Science Says the “Triune Brain” Model is Wrong

By now, defense attorneys are well aware of the “Reptile Theory,” a deposition and trial tactic adopted and advocated by plaintiff attorneys around the country based upon David Ball's and Don C. Keenan’s book, Reptile: The 2009 Manual Of The Plaintiff's Revolution. The Reptile Theory, the goal of which is to achieve exceptionally large verdicts, is a re-envisioning of the universally prohibited “golden rule” argument that asks jurors to step into the plaintiff’s shoes and perceive the defendant’s conduct at issue as a threat to their own personal safety.

The association of the “Reptile Theory” with “reptiles” is itself based upon a false, pseudoscientific premise of the “triune brain”—the notion that underneath the more advanced mammalian neocortex and the paleomammalian limbic system, humans have a primal brain structure, leftover from our evolutionary past, where survival instincts reside and emotional reactions to perceived threats occur. The Triune Brain theory roughly alleges that over the course of vertebrate evolution, new, more complex brain structures developed over the top of older structures that controlled more primal, survival-oriented behaviors—the “reptile brain.”

However, triune brain model, which arrived on the scene in the 1960s, has been debunked and is no longer part of current neuroscience orthodoxy. A recent commentary by Joseph Cesario, David J. Johnson and Heather L. Eisten, entitled “Your Brain Is Not an Onion With a Tiny Reptile Inside,” published in May 2020 by in Current Directions in Psychological Science, explains the flaws inherent in the triune brain model, stating that “[t]his belief, although widely shared and stated as fact in psychology textbooks, lacks any foundation in evolutionary biology,”

The authors explain that the appeal of the triune brain model lies in its simplicity:

Perhaps mistaken ideas about brain evolution persist because they fit with the human experience: We do sometimes feel overwhelmed with uncontrollable emotions and even use animalistic terms to describe these states. These ideas are also consistent with such traditional views of human nature as rationality battling emotion…They are also simple ideas that can be distilled to a single paragraph in an introductory textbook as a nod to biological roots of human behavior. Nevertheless, they lack any foundation in our understanding of neurobiology or evolution and should be abandoned by psychological scientists.

In one of our previous blog posts, we discussed particular strategies for defense attorneys to use in when filing motions in limine to challenge the use of Reptile tactics at trial. When challenging the use of Reptile tactics in motion practice, one should focus on explaining the tactic as a mere repackaging of prohibited “Golden Rule” arguments and should avoid getting bogged down explaining in detail the pseudoscience of Reptile.

Nonetheless, this paper’s commentary on the erroneous oversimplification of human brain anatomy suggests another way to think of Reptile. At its essence, Reptile oversimplifies and misrepresents the standard of care in a negligence action by framing legal duties as a combination of ill-defined “safety rules” that a defendant either did or did not follow. But the circumstances that led to litigation are likely nuanced and not reducible to an oversimplified list of binary choices, and the “safety rules” do not necessarily accurately or fairly reflect the legal standard of care.

Thinking of Reptile Theory as a reductio ad absurdum logical fallacy, given the facts of the case, can therefore help attorneys challenge the use of this tactic as an impermissible reframing of the standard of care.