It is said that two reactions to extreme danger are fight and flight. In the case of four-legged beasts, at least, we can add a third state: frozen (e.g., in the headlights).
Freezing in the face of a grave threat can extend also to human beings. Take victims of sexual assault, for whom non-resistance is sometimes used by defence lawyers to indicate consent.
In a commentary1 published in Nature Human Behaviour, bioethicist Ebani Dhawan and neuroscientist Patrick Haggard argue that an "understanding of neuroscientific evidence regarding involuntary immobility during RSA [rape and sexual assault] could prevent inappropriate victim-blaming."
Rape is sexual assault in the absence of consent, but the challenge for victims and prosecutors is in establishing lack of consent. Note also that saying yes to sex does not always mean consent, as that requires the freedom and capacity to be consenting.
Rape victims often report freezing in response to assault, and in the absence of scientific evidence defence lawyers may question whether there was a lack of consent. Dhawan and Haggard write that "legal actors in RSA cases are susceptible to stereotypes… about how a 'real' victim would behave."
With the help of existing evidence, Dhawan and Haggard show that immobility in response to extreme threat is likely to be involuntary. They suggest that involuntary immobility is a known neural threat response in which the brain circuits that provide voluntary control over bodily movement are blocked. This may trigger human immobility in much the same way that a rabbit can freeze when caught in the headlights of an oncoming vehicle.
Dhawan and Haggard note that 70% of women who undergo medical examination following a sexual assault report experiencing tonic immobility: a strong desire to escape danger, but an inability to do so. This, say the researchers, constitutes an "evolutionarily conserved involuntary response that is characterized by lack of normal voluntary motor control." They conclude that "our hypothesis of threat-induced involuntary inhibition of voluntary action pathways may contribute to improving understanding of the facts about RSA crimes, the societal wrongs of gender violence, and the realities of victims' experience and suffering."
Ebani Dhawan & Patrick Haggard, “Neuroscience evidence counters a rape myth”, Nature Human Behaviour (2023); doi:10.1038/s41562-023-01598-6.