The round-the-chin beard makes him look Amish, which he's not. It also makes him look like an anthropologist, which he is, but he denies growing the beard to look the part.
He just likes the look of it, so much so, he has not changed the style for near on 40 years. His wife Marie has never known him without a beard, says one of the world's most influential environmentalists as he sits outside the Hyatt in Auckland.
Professor Jared Diamond is a scientist, a genius and author of blockbuster books on man's impact on the environment and the environment's impact on man.
He is in the country to deliver a serious - deadly serious - and scary message about the world's future, which basically says that if we don't do something fast about matters of climate change, toxic waste, deforestation and so forth, the world as we know it will be over in 50 years.
But first things first. Diamond is happy to be side-tracked by a question about the role of the potato in 1800 Maori warfare, which features in his latest book Collapse.
The question goes something like "so, really, we should call the musket wars the potato wars?" Diamond's eyes light up. "That's right," he says.
The potato in New Zealand history is important. Collapse is about why some civilisations collapsed and others did not and what lessons we can learn.
It's a highly acclaimed book and a best-seller. On page 165 is a paragraph about how the arrival of the potato helped some Maori tribes raid other tribes much further away than they were previously able to.
The chapter of the book is actually about the fall of the Maya. The modest productivity of Maya agriculture and their lack of draft animals severely limited the duration and distance possible for their military campaigns, Diamond writes.
But a clear example of how improvements in food supply may decisively increase military success comes from the history of Maori in New Zealand, he says in the book.
Which brings us to the potato question.
"What made the musket wars possible were two things," he says. "Number one, muskets.
"But number two, there's no point sending off a troop of soldiers with muskets to wipe out other Maori for the next two months if they're not going to be able to feed themselves and as long as Maori were growing just sweet potatoes there wasn't enough to send out a Maori troop on musket wars."
When the European arrived and brought potatoes, Maori crop yields greatly increased.
"With potatoes, with the greater productivity, you could now send out troops for a month and feed them."
The potato was also important in the Maori conquest of the Chatham Island Moriori, he believes.
"The boat that brought the Maori to enslave and kill off Moriori, that boat was not full of sweet potatoes, it was full of potatoes. That was important."
Like the potato, Diamond is humble and immensely likeable. For someone so courted by the media, he still seems shy.
You get the feeling that probably he feels more at home in the New Guinean highlands which he loves and where he studied as a young man, making remarkable discoveries.
The tag "rock star" scientist does not appear to have gone to his head. In fact, he looks surprised to hear it. When it's pointed out he is a genius, he looks sceptical.
But genius he is. Diamond has incredible credentials. These are but a few. Early on in his life he re-discovered New Guinea's bowerbird which had been thought to have been extinct.
His 1997 book Guns, Germs and Steel won the Pulitzer Prize for non-fiction and traces why the dominant civilisations developed in Eurasia as opposed to other regions.
He has been described as one of the great minds of our time and is a recipient of the prestigious MacArthur Foundation scholarship, nicknamed "the genius award".
Now aged 69, his message does not get more serious. It is about the end of the world as we know it. If we go on as we are, within the next 50 years countries will become as Somalia, or Haiti, are now. Poverty stricken, lawless and stateless.
New Zealand, says Diamond, somewhat reassuringly, will be one of the best places to be, along with the New Guinean highlands.
Our environment is reasonably robust, we have rich organic soils and high rainfall, so it will be a better place to be than many other places.
"Oh come on," you might say, "you're being alarmist." Diamond will tell you the Somalia scenario is a worst-case scenario, that it is not too late to make changes. But look at how we are stuffing the world up.
"If we mess up in the next 50 years we will have messed up in an irreversible way. Namely, through climate change that we're not going to be able to reverse, and through widespread extinction of trees and birds [and animals]."
It is a horrible message. Does he get depressed about it? Diamond hesitates.
No, not depression, he says, but anger: "I get used to having a part of me that's angry. But one has to channel one's anger constructively. It's no good jumping up and down and raving and saying 'you people are terrible'."
He is laughing when he says "let's not talk about the people I would like to punch," but funnily enough the conversation turns to George Bush who he refers to as "my unfortunate president" and "the worst president of my lifetime."
When you ask why Bush is the worst, he says, "um, where to start. Lacks concern with reality. What science is, is the knowledge of reality. Our president, um, has little use for science."
Global warming is a good example. Diamond says there is virtual unanimity about the reality of global warming, yet Bush has denied that reality. Diamond adds that while Bush has not met with scientists, he has met with the popular fiction author Michael Crichton, who, incidentally, has an essay on his website titled "Aliens Cause Global Warming".
Diamond gives a short "no," when asked if he has read Crichton's books and when asked "but George Bush probably does?" replies "um, I don't know if he reads".
Then, he qualifies, yes, the President does read. But probably, only short accounts offered to him by his advisers.
If one just looked at the President, one could get depressed, he says. But on the other hand, within Bush's own party and his own advisers, there is hope.
When Collapse was published, a Bush appointee read the book and set up a meeting with Diamond and the Treasury Department.
He also had a call from the deputy chief of staff for Jeb Bush, the president's brother and the Governor of Florida.
Off the coast of Florida is Haiti and Florida has a big problem with Haitian refugees, boat people fleeing what Diamond describes as the poorest country in the New World. Collapse has a chapter on Haiti and Jeb Bush's deputy chief of staff wanted to brainstorm.
"The [deputy] chief of staff told me that he had that morning given Governor Jeb Bush my book and in the afternoon he was going to ask the governor what he thought."
He never found out, but credits Jeb Bush with setting up a taskforce on the matter. "So one shouldn't throw up the hands and say 'it's hopeless in the US, everybody's stupid'."
The conversation winds towards the subject of terrorism, and whether this relates to environmental factors.
Diamond says if he said the cause of terrorism was environmental damage he would be accused of exaggerating and being stupid - but if someone were to say environmental damage had nothing to do with terrorism, that person would be stupid.
"It's not an accident that terrorism tends to be supported in poor countries where people don't see other realistic choices for themselves because their country is very poor and ravaged."
Diamond is, among other things, professor of geography at the University of California, Los Angeles. He was born in Boston to a physician father and a mother who was a concert pianist, teacher and linguist.
He developed an interest in geography during World War II. "On the wall of my bedroom ... my father had two maps, one was the map of the Pacific, the other was the map of Europe, and every day dad would take the pins and move the pins to show the ships and battle lines."
Not everyone agrees with Diamond's theories. One dissenter argues against Diamond's premise that the people of Easter Island brought about their own downfall by wiping out their forest and driving their plants and animals to extinction.
In a recent American Scientist article archaeologist Terry Hunt argues rats were responsible for deforesting the island and the arrival of the European put paid to the people.
Diamond has an immediate response. Hunt, he says, is "dead wrong." There were rats on every single island of the Pacific, and these were not deforested by the rodents.
And ample archaeological evidence showed that by the time the Europeans arrived, people were burning sugar cane scraps because they did not have wood, and that they had long ago given up building canoes because they did not have wood - thus did not get the protein from the sea they once had.
He also has a message for New Zealand. Diamond read a story in the Herald this week about New Zealand's orange roughy management.
The story was about cutting the commercial catch limit because of scientists' concerns about the targeting of particular seamounts.
Diamond has a question. If we are still around in 100 years, let alone 50, will people look back and say "what were they thinking when they caught the last orange roughy?"
* Jared Diamond this week delivered the Sir Douglas Robb lectures at Auckland University.