He says that while many in the West see the brutality and fanaticism as unique to Islamic fundamentalism, the right cocktail of factors can make anyone an extremist. He sees five that could be at play with IS, the first simply that savagery begets savagery.
Callousness, aggression and lack of empathy are common responses by people who have been harshly treated themselves.
When the State breaks down, and with it law and order and civic society, there is only one recourse for survival – the group. Whether defined by religion, racial, political, tribal or clan – or for that matter by the brute dominance of a gang-leader – survival depends on the mutual security offered by the group.
And that can lead to seeing any other group as a dehumanised enemy.
In-group tribalism is strengthened – and loathing for the out-group correspondingly increased – where religion defines the groups. Even when aggression against the other group is self-destructive.
He believes that a culture of revenge can play a part, as can a blind faith in a leader.
The trouble is, as we have seen, when leaders choose to encourage savagery, not quell it, there is nothing hard-wired into human beings to stand up against it.
All that's well and good, I suppose, and some of Robertson's suggested motivations might make sense in the case of an Iraqi Sunni who has been victimised by members of the Shi'ite majority, and clings to a new group for survival in a lawless state as he seeks revenge for his woes.
But there doesn't seem to be much here to explain how a would-be British rap star ends up the prime suspect for cutting off another man's head, or why...
Dinosaurs may have just been unlucky that the catastrophic asteroid collision that is thought to have wiped them out arrived when it did. If it had hit the Earth earlier or later they might have survived, some scientists now think.
Steve Brusatte, a palaeontologist at Edinburgh University, says in a report in Biological Reviewsthat when the impact happened 66 million years ago the Earth had already suffered a dramatic loss of biodiversity and many of the big plant-eating dinosaurs, including the horned triceratops and duck-billed dinosaurs, had already disappeared.
And that meant there were fewer animals for the big meat-eating dinosaurs to prey on.
That made them just that bit less resilient when the asteroid hit what is now Mexico, setting off a disastrous chain of events including tsunamis and earthquakes, and forcing blankets of material into the atmosphere that blocked out the Sun and cooled the Earth by up to 10 degrees.
With ecosystems already weakened the dinosaurs didn't stand a chance, as Brusatte says:
The asteroid almost certainly did it but it just so happened to hit at a bad time when dinosaur ecosystems had been weakened by a loss of diversity. If the asteroid had hit a few million years earlier, or a few million years later, then dinosaurs probably wouldn't have gone extinct.
NASA has marked the 25th anniversary of Voyager 2's fly-past of Neptune in 1989 as the space agency prepares to get up close and personal with Pluto.
This picture of Neptune, above, was taken on 20 August 1989, at a range of 4.4 million miles from the planet. Voyager 2's closest approach to Neptune came four days later on 25 August.
The picture shows the Great Dark Spot and its companion bright smudge; on the west limb the fast moving bright feature called "Scooter" and the little dark spot are visible. North of these, there is a bright cloud band similar to the south polar streak.
NASA is also using the anniversary to set the scene for the climax another mission to the outermost edges of the Solar System in a little under a year when the New Horizons space craft does a similar fly-by of Pluto.
By coincidence, New Horizons passes the orbit of Neptune, its last orbit crossing before beginning its historic exploration of Pluto on the exact 25th anniversary of the Voyager 2 spacecraft’s encounter with the planet.
New Horizons will begin its Pluto exploration in January but the best pictures will come a little later when the spacecraft is at its closest.
New Horizons' Pluto encounter on July 14, 2015, will not be a replay of Voyager but more of a sequel and a reboot, with a new and more technologically advanced spacecraft and, more importantly, a new cast of characters. Those characters are Pluto and its family of five known moons, all of which will be seen up close for the first time next summer.