Professor Stephen Hawking was too unwell to attend a conference marking his 70th birthday, but delivered his speech via a recording.
Hawking was discharged from hospital on Friday after suffering an infection, but hadn't yet recovered enough to deliver the speech, at Cambridge University, personally.
The talk was titled 'A Brief History of Mine', and in it Hawking described his early life - and how his diagnosis with motor neurone disease at the age of 21 gave him the sense of focus that helped transform him from a rather lazy student into one of the world's greatest scientists.
At the time, he was told he had just a year or two to live. Motor neurone disease, also known as Lou Gehrig's disease, is generally fatal within five years of diagnosis.
"There didn't seem any point working on my PhD because I didn't know if I would live long enough to finish it," he said. "But then the condition developed more slowly and I began to make progress in my work."
Hawking also called for more efforts towards interplanetary travel, arguing that it was a necessity for the human race. "I don't think we will survive another thousand years without escaping beyond our fragile planet," he said.
Hawking told guests that it had been a wonderful time to be alive and exploring theoretical physics. And he had a word of advice for those who let themselves be discouraged by rather lesser adversity than he's had to face - pretty much everybody, in other words.
"Remember to look up at the stars and not down at your feet. Try to make sense of what you see and wonder about what makes the universe exist," he said.
"Be curious. And however difficult life may seem, there is always something you can do and succeed at. It matters that you don't just give up."
The full lecture isn't yet available, but will be published here.