Cantor's team reached the conclusion after years of tests using phallometry, an old method where a device measures blood flow to the penis when convicted sex offenders are shown nude images of children and adults of both sexes.
"We found that paedophiles share many physical characteristics. They are shorter, on average, than other men. They are three times more likely to be left-handed. Their IQs are about 10 to 15 points lower. They are also more prone to childhood head injuries," said the report published in Toronto Star, quoting Cantor.
"These physical characteristics are determined before birth, so the explanation for paedophilia must be in part prenatal," Cantor, an internationally respected clinical psychologist, was quoted as saying.
"It's become harder and harder to explain paedophilia on just (early childhood events). It's either purely biological or a mix of biological and experiential. But pure experience can't explain these data," he added.
Paedophiles are thought to be overwhelmingly men. About a third of those men prefer boys, about a third prefer girls, and a third will be attracted to both, the report added. Although female sex offenders exist, they are rare and it is more difficult to test their desires, the report added.
There is another school of thought too. "Not all sex offenders who target children are paedophiles, and not all paedophiles are sex offenders," Michael Seto, a paedophilia expert and forensic researcher with the Royal Ottawa Health Care Group, was quoted as saying.
Seto found that only 50 to 60 percent of convicted sex offenders are paedophiles. The rest have sexually abused children for reasons beyond attraction - personality disorders, chaotic households or violent impulses, the report added.