How do Charles Darwin's theory of evolution and James Lovelock's Gaia hypothesis complement or contradict each other?

Answer

Darwins' Theory of Evolution by Natural Selection says that species either adapt and evolve via an accumulation of sequential minor variations, or become extinct.

The Gaia hypothesis says that the planet's biomass self-regulates the conditions on the planet to make its physical environment (in particular temperature and chemistry of the atmosphere) on the planet consistently hospitable to the species which constitute its 'life'. For example, when atmospheric carbon dioxide levels rise, the biomass of photosynthetic organisms increases and thus removes more carbon dioxide from the atmosphere. Gaia has attracted considerable debate and should, at this stage, be considered a hypothesis rather than a proven theory.

The two concepts are parallel in that they explain the ability of an 'organism' to adapt to the changing environment. However, one is concerned with biological processes, while the other is concerned with macro-physics. They neither contradict nor support each other.