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The mid-20th century saw a dramatic rise of serial killers in the United States, with notorious names like Ted Bundy, John Wayne Gacy and the Zodiac Killer dominating popular culture.

This era, known as the “golden age” of serial killers, started to decline in the 2000s. But there could be a surge once again, at least according to Peter Vronsky, a Toronto-based historian and author.

READ MORE: What we know about suspected Toronto serial killer Bruce McArthur

Vronsky’s latest book, Sons of Cain: A History of Serial Killers from the Stone Age to the Present (a reference to the biblical story of Cain, who murdered his brother, Abel) argues that traumatic events in history, such as the Great Depression, the Second World War and the 2008 world financial crisis, shaped serial killers.

His book also examines the long history of serial killers — before the term was coined in 1981. He argues that all humans, not just a few, are wired to be killers and it stems from our hard-wired DNA from our ancestors who had to kill to survive.

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WATCH: A look at past serial killers in Toronto

1:50 A look at past serial killers in Toronto A look at past serial killers in Toronto

What caused the ‘golden age’ of serial killers in the mid-20th century?

Between 1970 and 1999, Vronsky argues there was a surge of serial killers in the United States. So where did they come from?

“A serial killer’s psychopathology is formed in childhood, between five and 14. They don’t really commit their first murder, on average, until they are 28. So if we look at those three decades, the John Wayne Gacys, the Ted Bundys … you have to back them up about 25 years into their childhood, and that puts them as children being raised by a World War Two generation, a post-depression-era generation,” he says.

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He adds that the family plays an important role in many serial killers’ lives. Many fathers who came back from the war traumatized and suffering from post-traumatic stress disorder may have been mentally or physically absent as a parent.

“My hypothesis is that we have to be looking at the parents of those serial killers,” he says. Tweet This

“We fought this horrific monstrous enemy during the war, and we had to be as monstrous to defeat that kind of enemy,” Vronsky adds. “So you have a generation of World War Two veterans who returned and remained in a sullen silence, unable to share with their families.

I think a combination of these factors contributed to this golden age.”

In this 1977 photo, serial killer Ted Bundy, centre, is escorted out of court in Pitkin County, Colo. Glenwood Springs Post Independent via AP

Is another surge of serial killers on the way?

There could be another rise of serial killers in 2030, according to Vronsky. And the market crash of 2008 could have been a catalyst.

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“In the exact same way the trauma of war and Great Depression produced the golden age, there seems to be the same mix. A lot of kids lost their homes and had families that were broken because of a broken economy,” he says.

“If my hypothesis is correct, 20 years down the road, we’re going to see some serial killers emerging out of it,” he adds. “Serial killers appear in surges, and surges are related to trauma and family breakdown.”

READ MORE: 5 Canadians on what social media is doing to their mental health

Michael Andrew Arntfield, a Western University criminology professor, says this theory could be correct.

“I think that it is plausible,” he says. “Social media, superficiality and a lack of a family safety net as a result of recession … this has already been a driving force behind other issues. So it could happen due to a massive cultural shift.”

Can technology help counter this?

There has been an overall drop of homicides since the 1990s, meaning serial killers are either getting better at what they’re doing, or there are fewer killers out there, Vronsky says.

But there are new investigative techniques, such as DNA matching, that help apprehend these killers. For example, this year, a DNA match led to the arrest of the suspected “Golden Gate Killer,” linking back to sadistic crime sprees of the 1970s and ’80s — a string of at least 13 slayings and 45 rapes in California.

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Cellphone technology has also made is very difficult for the perpetrator to commit these acts, he adds.

However, Arntfield argues that the opposite is true.

“On the contrary … there has been a decline of homicide solve rate over the past five years,” he says. “More murders in the U.S. go unsolved than before DNA was used.” Tweet This

According to his database he helps run, The Murder Accountability Project, technology can actually hinder an investigation.

“The theory is that police are overly depending on the automated systems and lost the investigative intuitions,” he says. “It also seems that fewer people are co-operating with police and there are more reluctant witnesses.”

WATCH: Former police officer arrested in ‘Golden State Killer’ cold case

1:25 Former police officer arrested in ‘Golden State Killer’ cold case Former police officer arrested in ‘Golden State Killer’ cold case

Are we all born killers?

Another argument Vronsky makes in his book is that “aggressive instincts” are hardwired in us. Infants are all potential serial killers, but we get “unmade” with socialization, healthy parenting and a good environment. He said we are taught to inhibit out sexual and aggressive impulses.

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READ MORE: Alleged serial killer Bruce McArthur ‘likely a psychopath’, expert says

But for the few that socialization breaks down, either through trauma or socialization problems, these people remain in “that natural state” with these instincts that are much more developed, he said.

Vronsky argues that these “survival instincts” are engrained in our reptilian brains, and have not been phased out of our biology. Humans’ tendency towards killing dates back tens of thousands of years to the clash between Neanderthals and Homo sapiens.

But there is also reason to believe the opposite is true, according to Arntfield.

“It is in our evolutionary interest to co-operate and help one another,” he says. “You’re dealing with a very small percentage of the population who have sexually-motivated homicides. These people have a fundamental, biological or environmental flaw that rerouted natural wiring.”

(Original Caption) San Francisco: San Francisco police circulated this composite of the Bay Area’s “Zodiac” killer. Getty Images

What makes a serial killer?

Childhood trauma is a very common theme among serial killers, Vronsky says. It could either be in the form of an absent father figure, not bonding with a mother as an infant, rejection by peers or loneliness.

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However, there are millions of children that grow up with abusive families or have absent parents, and they do not all become serial killers, he added.

“We are still looking for the ‘X’ factor on what makes a serial killer.”

Suspected serial killer, Bruce McArthur

Vronsky says he has been paying very close attention to the case of accused serial killer, 66-year-old Bruce McArthur, who has been charged with eight counts of murder by Toronto police.

“His age is very interesting. If he was statistically an average serial killer, then he could have been killing as early as the 1970s,” he says.

Toronto police say they don’t believe McArthur is linked to any other murders — except for the eight he is charged with.