The human race is in a period of 'hypermobility' as people move within and between countries more than ever before.
It's the highest level of mass migration seen since World War II, says demographer professor Paul Spoonley.
So what's going on?
Some of the movement is voluntary – for economic factors and work opportunities; some of it is forced – refugees and asylum seekers fleeing conflict or oppression, Spoonley tells Jesse Mulligan.
Countries which were once 'emigration' countries, such as Germany or the UK, have become 'destination' countries.
"You could probably argue those countries aren't getting enough immigrants, they have declining fertility, an ageing population and a shortage of skills. So where are you going to get them from domestically? That's a challenge we all face as advanced OECD countries."
Yet these influxes have led to mass anxiety writ large in the forms of Brexit in the UK, the rise of nationalist, populist parties in Europe and the Trump presidency in the US, Spoonley says.
"There's a sort of political anxiety, but there's also an economic anxiety and it's not to be wondered why. People in the mid-west [of the US] who are facing very significant economic changes are also wanting to understand those changes and for some of them at least immigration is the reason why they are losing jobs, or their culture is being 'overrun'."
This anxiety manifests as an overestimation of immigration numbers.
"The rule of thumb is in countries which are anxious about migration, people tend to double the number that are there."
In the US, documented and non-documented immigrants make up 13.5 percent of the population – yet many Americans questioned in a recent survey estimated the figure to be 35 percent, he says.
"In the UK, the immigrant population is 13 percent, yet most people think 30 percent of British people are immigrants."
Refugee and asylum flows are now are as big as they were at the end of World War II, Spoonley says.
The war in Syria has generated a massive tide of displaced humanity, which has led to significant political tension in Europe where many Syrian refugees have been resettled.
But it is not the wealthy nations of Europe that have borne the brunt of this influx, he says.
"A lot has been made about the fact they are moving into Europe, but in fact easily the largest numbers [being settled] are in Lebanon and Turkey.
"Lebanon has 4 million people and has taken 1 million refugees – it's an enormous challenge for them"
Germany has been very generous in terms of accepting refugees, Spoonley says, as have the Scandinavian countries.
But we now see a political backlash with 20 percent of votes in Europe going to populist anti-immigration parties.
New Zealand's response to the refugee crisis has been lacklustre, he says.
We take 750 refugees a year and have done since the 1980s.
"Compared to both Australia and Canada, we're low. Australia last year had 12,500 refugees and so proportionally we are way behind the eight-ball.
"With those 22 million refugees around the world, I think we need to ask the question what is our responsibility?"
One of the great historical migrations to date is happening now within China, he says.
"Currently we're seeing the largest migration of people in human history. 350 million people have moved from rural to urban areas and that's creating these enormous megacities."
Along with India, China exports large numbers of skilled people.
But as the country's birth rate drops, Spoonley anticipates that will change.
The replacement fertility rate in China is currently 2.1 children per woman, and in the city of Shanghai it is 1 child per woman.
"At the moment there's an excess of skills, but it's not going to last."