Exploring the wealth of material available from the Richard Dawkins Foundation, I came across a series of five one-hour lectures given by Dawkins in 1991. These are that year’s Royal Institution Christmas Lectures for Children. Don’t be put off by the “for children” bit, though. Dawkins presents the information in a very mature and entertaining way. Many of the themes he uses in his more recent talks can be seen here.
From the YouTube playlist info:
Oxford professor Richard Dawkins presents a series of lectures on life, the universe, and our place in it. With brilliance and clarity, Dawkins unravels an educational gem that will mesmerize young and old alike. Illuminating demonstrations, wildlife, virtual reality, and special guests (including Douglas Adams) all combine to make this collection a timeless classic. The Royal Institution Christmas Lectures for Children were founded by Michael Faraday in 1825, with himself as the inaugural lecturer. The 1991 lecturer was Richard Dawkins whose five one-hour lectures, originally televised by the BBC
Despite being filmed 20 years ago, there is little to date these presentations except the computer technology (this pre-dates the web) and Dawkins’ choice of shirts 
