Cruelty by Nature: The Science of Intentional Abuse

by Peter Salerno PsyD

Why do some people manipulate, exploit, and harm with chilling consistency—while others, even when raised in the same environment, do not? Cruelty by Nature dismantles the comforting myths that abuse is merely the product of trauma, bad parenting, or social wounds. Instead, it draws from neuroscience, genetics, and clinical psychology to reveal a sharper personality pathology is rooted in stable biological systems that bias individuals toward exploitation.

Dr. Peter Salerno, a retired licensed psychotherapist and expert in personality disorders, blends rigorous research with survivor testimony to illuminate the circuits, chemistry, and strategies that drive narcissistic, psychopathic, borderline, and histrionic abuse. From altered brain networks and neurotransmitter imbalances to the cold logic of instrumental cruelty, this book makes clear that abuse is not an accident of hurt people “acting out”—it is often intentional, calculated, and biologically sustained.

More than a scientific account, Cruelty by Nature calls for a cultural shift. By moving beyond trauma-only narratives, we can better protect victims, hold perpetrators accountable, and advance psychology as a true science. Survivors will find their experiences validated; professionals will find new frameworks for treatment, prevention, and justice.

Challenging, uncompromising, and deeply necessary, Cruelty by Nature reframes the conversation about abuse. It is a manifesto for understanding human cruelty as it is—not as we wish it to be—so that healing, justice, and change can finally take root.

Genres: Psychology, Audiobook, Nonfiction, Self Help, Mental Health

184 pages, Paperback

Published October 31, 2025

Reviews

[Pyroclastic Ash · Rating 5 out of 5]

Want to gain some understand of the cruel nature of some people? Want to know if it is innate or intentional? Want to get an overview (just an overview, not super in-depth) of Cluster B personality disorders and some behaviors?
Read this.

[[Name Redacted] · Rating 5 out of 5]

The Rousseauean idea of the "Blank Slate" which has undergirded 90% of Western political theory, legal theory, philosophy, psychology, art, etc. for most of the last century was utter bollocks. People are not simply victims of society, but hardwired for certain tendencies. And we are currently reaping the whirlwind which came from so carelessly sowing the Rousseauean seed.

Likewise, popular culture has grossly misrepresented (due either to ignorance or malice) the reality of disorders like psychopathy or anti-social personality disorder.

There is no "Blank Slate."

"Hurt people hurt people" is a comforting lie.

The role of epigenetics has been vastly overstated.

Your ex-boyfriend/husband almost certainly wasn't a literal Narcissist.

Your ex-girlfriend/wife almost certainly wasn't Borderline.

Most psychopaths aren't serial killers, especially not brilliant ones.

The reality is that personality disorders like Narcissistic Personality Disorder, Psychopathy, Histrionic Personality Disorder and even Borderline Personality Disorder are effectively uncurable because they are grounded in genetic and neurobiological realities. Environmental factors may "activate" these personality disorders in some individuals (just as with autism spectrum disorders), but they also often manifest in individuals whose environments were ideal. Because those individuals were biologically, genetically, neurobiologically inclined to the development of those personality disorders. The dice were rolled with every birth and sometimes they come up snake eyes.

These people aren't victims of society, bad parenting, trauma. Their actions aren't mistakes. They aren't accidentally or unintentionally cruel. They understand very, very well what they are doing because they are generally EXTREMELY empathic. They simply don't care; or, more precisely, they see cruelty, manipulation, deceit, etc. as useful tools and regard those they hurt as fools or weaklings who deserve what is happening to them. If they think of them at all. They KNOW they are hurting others, but lack the biological capacity to sympathize or care that they have hurt someone else. They exist within a sort of solipsistic realm, a world in which they are the sole "human" reality and everyone and everything else is simply an object or an obstacle or a resource for them.

Again, there is no "Blank Slate." They are not innocent. They aren't victims of society. They are choosing to be cruel in full knowledge of the harm they are causing because it is advantageous to them and unless we as a society make it disadvantageous to be cruel...unless we execute or imprison them without any possibility of parole or escape... Well, they'll just keep on doing it. And they won't feel a thing.

[Saint Eli · Rating 4 out of 5]

everyone is responsible for their actions

[Cheryl Jensen · Rating 5 out of 5]

Dr Salerno articulates some discomforting feelings I have had when hearing accounts of the brutal and callous actions of those with narcissistic, borderline personality disorder, and psychopathic tendencies. (He also includes the histrionic personality, which I was not familiar with.) While recognizing there is real brain chemistry behind these personality disorders, the author challenges the current mindset that the abusive behaviour of many of these people is due to the trauma or abuse they have suffered in their own lives. This paradigm tends to excuse these individuals for the outrageous abuse and manipulation of their victims, and causing these victims feeling their own suffering is somehow not the abuser's 'fault,' which creates a further gaslighting of their experience.

Dr. Salerno postulates these personality types deliberately choose their abusive behaviour in order to get what they want, and are fully in control of their actions. Having the personality disorder does not negate nor excuse their toxic and manipulative behaviour. He explains the biology and genetics involved in creating these personality disorders, and provides the reader with ways to recognize when these individuals are being abusive/manipulative, their patterns and strategies, and red flags. It is helpful in informing current and possible future victims in protecting themselves and hopefully avoiding entanglements with these toxic individuals.

[Chloe Dean · Rating 3 out of 5]

I picked up this book purely based on the title haha, and it was a nice surprise for someone like me (I'm a neuroscientist). It provided great insight into the neuroscience behind particular personality types, and helped with debunking common misconceptions about abuse, such as "hurt people hurt people".

However, I think the book would have benefited from deeper case study examples and referenced literature. It ended up being pretty repetitive, with a large portion of the book being the appendix. I would have liked victims to have a bigger voice.

I walked away from this book understanding that people who commit intentional harm likely are genetically predisposed to that type of behaviour - but I still feel like this is quite a broad claim, and actually abusive behaviour is very nuanced. Hence why I think case studies would have been beneficial here.

I would have appreciated if the author really acknowledged that nuance, and said for the purpose of this book, he would focus on th genetics and physiology behind hurtful behaviour. Instead, it felt a bit like he was drilling that all abuse arises from people genetically inclined to behave that way. I don't think that's necessarily true. Does every who behaves like this really have some "evil" polymorphism? I don't know.

Regardless, a quick and interesting read. My neuroscience knowledge is primarily in synaptic transmission, so this was a new area for me to learn and I appreciate that.

[Mary · Rating 2 out of 5]

Not impressed. Although the topic is compelling, the book lacks clinical data or case studies. The author makes massive generalizations about human psychology. On top of that, a huge portion of the book is just the appendix and index, leaving very little actual reading material. It is highly repetitive, padded out, and lacks scientific authority.

[Renee Godwin · Rating 4 out of 5]

fascinating

Mind-blowing revelation that goes against everyone we thought we knew about these “creatures”. Dr Salerno repeats himself a lot, which makes up about 40% of the book. This is still a must- read for anyone who has been targeted by one of these cluster B personalities.

[Varsha Chandra · Rating 5 out of 5]

Uniquely insightful.