The struggle for existence holds as much in the intellectual as in the physical world. A theory is a species of thinking and its right to exist is coextensive with its power of resisting extinction by its rivals.

The choice however is as clear now for nations as it was once for the individual: peace or extinction.

And I have lived since - as you have - in a period of cold war during which we have ensured by our achievements in the science and technology of destruction that a third act in this tragedy of war will result in the peace of extinction.

The government of the United States is a device for maintaining in perpetuity the rights of the people with the ultimate extinction of all privileged classes.

Doctors dressed up in one professional costume or another have been in busy practice since the earliest records of every culture on earth. It is hard to think of a more dependable or enduring occupation harder still to imagine any future events leading to its extinction.

Freedom is never more than one generation away from extinction. We didn't pass it to our children in the bloodstream. It must be fought for protected and handed on for them to do the same.

At issue was the question whether this man's faith could prevail against a man whose equal faith it was that this society is sick beyond saving and that mercy itself pleads for its swift extinction and replacement by another.

It's a matter of life and death for this country. The Kenyan forests are facing extinction and it is a man-made problem.

The death of democracy is not likely to be an assassination from ambush. It will be a slow extinction from apathy indifference and undernourishment.

The damage that climate change is causing and that will get worse if we fail to act goes beyond the hundreds of thousands of lives homes and businesses lost ecosystems destroyed species driven to extinction infrastructure smashed and people inconvenienced.