"We are a plague on the Earth. It's coming home to roost over the next 50 years or so. It's not just climate change; it's sheer space, place to grow food for this enormous horde. Either we limit our population growth or the natural world will do it for us, and the natural world is doing it for us right now," Attenborough told the Radio Times.
The 86-year-old Attenborough is also a patron of the Optimum Population Trust, a think-tank on population growth on long-term sustainability, quality of life and the natural environment, specifically natural resources, climate change, and biodiversity.
He spoke out earlier about the "frightening explosion in human numbers" and the need for investment in sex education and other voluntary means of limiting population in developing countries.
"We keep putting on programmes about famine in Ethiopia; that's what's happening. Too many people there. They can't support themselves - and it's not an inhuman thing to say. It's the case. Until humanity manages to sort itself out and get a coordinated view about the planet, it's going to get worse and worse."
Attenborough, whose landmark series are repeated from Monday on BBC2, starting with Life on Earth, has also spoken out about the change in wildlife documentaries during his lifetime.
He said commentary from presenters like himself were becoming less necessary as the camera work itself was able to narrate the stories.