BBC - Barack Obama has told an audience in Glasgow that hope is worth fighting for despite big challenges facing the modern world.
The 44th president of the United States said online platforms had shifted in recent years to focus on content that stoked anger and fear, but he believes a drift to extremism is "not inevitable".
The comments came as he addressed an OVO Hydro crowd of 12,150 people while in conversation with British journalist and author Sathnam Sanghera, part of three speaking dates in the UK.
He reflected on his time in the White House and examined the political and social challenges facing the US and the wider world.
But he said the same positive forces and tools that could mobilise people around democracy or human rights could also be used by hate groups.
He said they "connected people for good, but also for ill".
"It turns out that the reptilian side of our brain really gets attracted to anger, fear, resentment and the sense that someone is out to get you," he said.
"So a lot of social media and a lot of our information is informed around that."
But the former president, who has already spoken in Belfast and will appear in Manchester on Thursday night, said that a drift towards extremism was "not inevitable".
He added: "After World War Two, at least in the United States and certainly in Europe as well, the federal government said 'we're going to set up some rules because we've seen what propaganda can do in the hands of somebody like Hitler.
"We can see how big lies and misinformation can distort and enrage and incite violence. So we're going to hold these folks responsible'."
"We have not chosen to do that."
Obama, who was president until 2016, said there was a "critical balance" that must be struck between free speech and regulation.
But the 65-year-old said that the world and its leaders are going to need to find mechanisms and new institutions to allow rigorous debate and disagreement while helping people sort out basic facts.
He said: "If I had a blame pie for why politics is so polarised and why we're seeing a rise of populism in many places, it's because of that information that is going into our brains every day."
Obama said this resulted in young people feeling discouraged, and that "it's not a healthy diet that our brains are on at the moment".
He added that he feared this could become even worse with AI making it hard to distinguish between what is true and what is not, something he believes will make democracy hard to function.
'People forget lessons from the past'
Speaking about hope, Obama was asked if he still believed in a Martin Luther King Jr phrase he quoted years ago, about the arm of the moral universe being long, but ultimately bending towards justice.
The former president said that he still stands by the quote and argued that hope is an active "almost theological" choice people must make.
He said: "It is a decision about how do we face and embrace this finite amount of time we have on the planet."
He told the audience he believes it is healthier for people to believe that change is possible.
"I think when we act on that basis, it doesn't always work out, but over time things do get better," he said.
Obama also said there seems to be a cycle in humanity where people forget lessons learned from the past and start to take things for granted.
"We start thinking 'maybe using language in public from our politicians that fosters hatred and scapegoats certain people – immigrants, Jews, or blacks or gays – that's just talk, it's humour'."
He said people forget where that can lead to, with them becoming less tolerant.
Obama told the audience that the world is going to be dealing with "big challenges", but he said he thinks "we can be better" and that making the world better remains worth fighting for.