My apologies for being lazy and not reading all the responses here, but what was Dr Fenner's predicted cause or causes for humanities extinction ?

I want him to be wrong, but with dwindling natural resources and climate change, I'm not so sure he's not right. Governments don't seem to really be doing enough to try to reverse the effects of climate change. Unless climate change is complete bogus, and it doesn't seem like it is because an astounding amount of scientists have shown the data and agree something needs to be done 5 minutes ago. Dwindling resources between nuclear powers doesn't seem like it can go in any right direction knowing how humans have been in history.

Here is the link you were too lazy to post [phys.org]

Neo-Malthusians are a dime a dozen. The chances Fenner was correct are very low.

Could happen. There’s nothing to be afraid of. We’ll just do the best we can and go with the flow.

I'm just waiting for the Yellowstone Super Volcano to finally blow and wipe us out. I could see that happening in the next century.

Mass extinction can occur in many ways; the more of them we find possible, the more likely we will be affected. There are things that will improve our chances for existing longer, but atm it extinction seems very possible. I think the pendulum can swing the other way, and assure our existence.

I disagree.
I believe we will prevail.
We've successfully adapted to every climate on the planet so far. We don't need to depend on evolution. We're at the point of being able to build artifical ecosystems, move into space, the oceans, maybe other planets in our solar system. We're able to modify and manipulate genetic makeup. We'll be ok. Maybe different. But ok.

He may have been wildly optimistic but he was also wildly speculative. IMHO