Charles Darwin and Mars? Where's the connection? The BBC's Howard Falcon-Lang, talking to ecologist Dave Wilkinson, says it lies in a little-known experiment on an island in the South Atlantic. Darwin apparently came across Ascension Island, a desolate mound of volcanic ash, in 1836. He thought it would be a great site on which to create a "Little England"--an entirely artificial ecosystem. Coincidentally, the Royal Navy also used the island as a "strategic base," but had difficulty procuring fresh water. Thus began, in 1847, a joint enterprise of Darwin's botanist friend Joseph Hooker, the navy, and the Royal Botanic Gardens at Kew:

The idea was breathtakingly simple. Trees would capture more rain, reduce evaporation and create rich, loamy soils. The "cinder" would become a garden.

So, beginning in 1850 and continuing year after year, ships started to come. Each deposited a motley assortment of plants from botanical gardens in Europe, South Africa and Argentina.
The reason modern ecologist Dave Wilkinson finds this "really exciting" is that these 19th-century folks essentially created their own habitable ecosystem:

Wilkinson thinks that the principles that emerge from that experiment could be used to transform future colonies on Mars. ... "It's a terrible waste that no-one is studying it," remarked Wilkinson at the end of the interview.