Darwin's perspective on the origin of species is useful to us because it is non-deterministic, non-teleological, and ecocenteric. In Darwin's "tree of life" Homo sapiens are not at the top of the pyramid but on the same evolutionary level as other life forms. In fact, from an evolutionary perspective Homo sapiens are yet to prove their fitness the same way sharks or other species with much longer history have.
The Gaia hypothesis (names after the Greek mythology supreme goddess of Earth) proposed by James Lovelock, provides further context for reflection on Our Place in the World. A British scientist, in the 1960s Lovelock served as an independent consultant for NASA in planning for the Viking mission to Mars. NASA was interested to learn about how best to determine if there is life on Mars.
Lovelock realized that one does not need to land on Mars to know if there was life on it. Atmospheric conditions on Mars (carbon dioxide 95%, oxygen 0.13%, nitrogen 2.7%), stable for very long time, precluded existence of life, as we know it on Earth. Lovelock then asked what are the preconditions of life on Earth? Using a chemical model of Earth without any life forms (no photosynthesis or respiration), he found that carbon dioxide would be 98% (currently 0.03%), oxygen barely detectable (currently 21%), and nitrogen less than 2% (currently 79%). Furthermore, such a lifeless Earth would be very hot at 554F/290C with atmospheric pressure 60 times of what exists today.
Lovelock defined Gaia as a complex entity involving the Earth's biosphere, atmosphere, oceans, and soil, the totality constituting a feedback or cybernetic system, which seeks an optimal physical and chemical environment for life on this planet.
Columbia University ecologist, Shaheed Naeem, explains it in simpler terms:
Lovelock came away with a sense that there was something truly remarkable about Earth, a sort of meta-life or gigantic global biological system in which the sum of the parts--all the plants, animals and microorganisms--made Earth the habitable planet that it was. He speculated that it was an autopoietic system, meaning (roughly) that all its species actively contribute to the functioning of the biosphere in such a way as to ensure their growth and regeneration, which, in turn, is what governs biospheric functioning. This is a complex idea, but essentially he felt that life actively holds the conditions of Earth's surface within a range conducive to the persistence and perpetuation of life, a homeostasis similar to our bodies' regulation of core temperature to a constant of around 37 C (98.6 F).
The Gaia hypothesis was initially ignored or ridiculed by some as some kind of neo-pagan New Age religion. Renowned scientists such as such as Doolittle, Dawkins and Gould criticized it on various grounds (click here).
However, in 1980s the Gaia hypothesis received positive recognition by scientists and a number of scientific conferences have been held to develop and implement it as a research agenda.
Climatologist Stephen Schneider who organized the first Gaia conference in San Diego in 1988 proposed that the Gaia hypothesis includes a range of possible claims. Naeem summarize these as the Weak Gaia Hypothesis that says life is critical to Earth’s environment, and the Strong Gaia Hypothesis that says that the biosphere is autopoietic. He notes:
Though the jury is still out, the bulk of the scientific evidence is against the Strong Gaia Hypothesis. One of its strongest critics is Dawkins, who sees no way that evolutionary or ecological processes can generate an autopoietic biosphere from a seemingly unstructured confederation of species whose fates are determined by their individual fitness or stability of the community, ecosystems or biosphere they reside in. Nevertheless, life is what makes Earth habitable, so the Weak Gaia Hypothesis is undeniable.”
While we wait for the future assessment of the Strong Gaia Hypothesis, the consensus on the Weak Gaia Hypothesis offers materialist and scientific grounds for a view of "web of life" in addition to Darwin's "tree of live". Life on Earth is inherently interdependent. This validates ethical principles of Deep Ecology ’s Eight Point. It also offers a framework for rethinking Marx’s vision of de-alienation of humans from nature.