On Monday night's Q&A, a celebrated American guest was taking no prisoners - and Tony Jones was taking no nonsense.

Paul Ehrlich took issue with the host. He took issue with the audience. He took issue with his fellow panellists. He did so with gusto and gumption and mostly, it seemed, in slightly brittle good humour - all qualities necessary when critics have been telling you for most of your nearly 50 years on the public stage that you've got almost everything wrong.

This does not deter the author of 1968's doom-laden tome The Population Bomb: one thing Ehrlich can do is talk - through his hat at times, and probably underwater - but boy, can he talk.

He came, he saw, and while he never quite conquered, he was never in danger of conking out. At 83, Ehrlich is indefatigable.

We had a taste of things to come on only his second answer - on population growth, and whether he still regarded it as a problem - which invited an interjection from Jones.

Jones: "Paul, can I just interrupt you?"

Ehrlich: "No, I don't like to be interrupted, actually."

This was said with a laugh and a smile, but you were a fool if you thought he was kidding. His exchanges with Jones took on an added edge the longer the program went on, possibly because the host made the necessary observation that his guest had a less than stellar record of making accurate predictions.

"You have been wrong a few times in the past, Paul, you would admit, wouldn't you?" Jones inquired.

Ehrlich: "Look, any scientist or anyone who has talked about the future and never been wrong wouldn't be sitting on this show."

Jones: "Can I just mention one to you. 1971, you said that by the year 2000 the UK would be a small group of impoverished islands inhabited by 70 million hungry people. Was that just wishful thinking?"

Ehrlich: "They're not hungry but otherwise it's accurate. The thing we're most accused of..."

Jones, interrupting: "It's a pretty rich little country, Britain. I mean, it's not that accurate really, is it?"

Ehrlich: "No."

Ehrlich went on, only to be stopped short by Jones again: "I've got to come to another question."

"OK," said Ehrlich through gritted teeth, waving his hand in Jones's direction. "You got shills out there, that's good."

Jones: "No. They're not shills, these are people asking questions."

For anyone unfamiliar, a shill is a stooge - or to put it another way, an audience plant of the type that Tony Abbott saw lying in wait for every Coalition minister who fronted what the former PM called "a lefty lynch mob". Could it be that Ehrlich had taken Q&A tips from another man fond of delving into a personal collection of doomsday scenarios? Whatever the case, the professor was intent on remaining eccentrically contrary.

Invited to contribute to a question that had just been debated by the rest of the panel, he began with this assessment of his fellow guests: "Mostly nonsense, unfortunately." And when he quoted the long-standing message of billionaire Dick Smith on population growth - "[Smith] says big Australia is a crock" - Ehrlich took umbrage that would have done Tony Abbott proud when Jones tried to move on.  

"Oh sorry, I shouldn't say Dick Smith is absolutely right here."

Jones: "No, no, I didn't say that at all. I want to move on to other subjects ..."

In all, it was a memorable Ehrlich turn, which is not to say he took over the show.

His fellow panellists had their say, mostly effectively, on issues ranging from the GST debate to the national anthem. Wendy Harmer, who has been gracing ABC studios with wisdom and wit for nigh on 30 years, showed that she remains an essential gadfly in the national conversation, keeping the pollies honest. Diversity champion Dai Le, was a welcome voice on that issue and  on matters of immigration and population.

And the pollies? There were the standard two - Liberal Senator Simon Birmingham, the new Education and Training Minister, and Tony Burke, Labor's finance spokesman. The pair kept it civilised, but you'd have to award the night to Birmingham on points - if only thanks to the memorable knot  Burke tied himself in when debate turned to the Gonski education reforms.

"On Gonski, my advice is do it," Burke implored the minister, re-emphasising his point with passionate insistence: "Do it! Do it!"

Cue applause. But Birmingham promptly turned the question back on his Labor foe - would Labor commit to funding Gonski as he was demanding of the government? - a question that sent Burke down a rhetorical rabbit hole from which he never fully returned.

"We are in the process now of having to come up with new funding..."

Tony Jones: "Hang on, hang on, didn't you just say, 'Just say yes'? It's a simple answer."

Burke soldiered on. Jones persisted: "Can you say yes to that particular question?"

"We are committed to the Gonski principles. Yes, we are committed to the Gonski principles."

Jones: "And the Gonski funding?"

Burke: "Yes, we are committed to the funding that delivers the Gonski principles."

Jones: "Why was it so hard to get you to say that?"

Not for the first time last night, Tony Jones had put a waffler in his place.