Phylogenetic Evidence for the Early Origin of the Homeostatic Influence of the Biota on Planetary-Scale Geophysical Processes
Authors: Leggett Mark , Ball David A. 
Published: September 2023

This paper uses empirical evidence to address the subject of when and how Gaia arose. To set the scene for this, the paper first proposes two core necessary attributes for Gaia: each individual having control systems and joint action of groups of such individuals producing results that are more beneficial to the group than would have arisen from the isolated action of each individual. We make the case that the predominantly recognised “planetary” nature of Gaia is a contingent rather than necessary attribute. The paper next identifies representative examples in contemporary organisms of each of the two core attributes of Gaia in operation. For each of these examples, genes making up part of the genetic specification of the example were identified. We then sought these same genes in the earliest examples of life that have been genetically characterised in empirical terms - the Last Universal Common Ancestor (LUCA) and the Last Bacterial Common Ancestor (LBCA). These arose respectively between 4 and 3.5 billion years ago. Examining both the pools of known modern genes and demonstrated LUCA and/or LBCA genes, sufficient relevant modern genes were also found in LBCA and/or LUCA to provide empirical evidence that the core attributes of Gaia were present in LBCA and/or LUCA. Hence, we claim that the first Gaia likewise arose between 3.5 to 4 billion years ago. The paper also provides case studies showing similar results at increasing scales of organismal aggregation over the intervening period to the present. Dawkins (1982), defining Gaia as was predominantly done then in terms of its planetary attribute which posits that there is _one _Gaia on Earth, pointed out that neo-Darwinian natural selection requires competition between _multiple _units of selection. Given the absence of such multiple units of selection, Dawkins proposed that Gaia could not come into being by neo-Darwinian natural selection and therefore did not exist. The present study provides evidence that Gaia can exist at a range of scales greatly below planet level and that genes for the core attributes of Gaia have been available at these lower scales from near the start of life. With such genes being units of selection, planetary Gaia can come about by a series of developments commencing near the start of life, each involving standard gene-based Darwinian natural selection. We consider these results to resolve the issue raised by Dawkins (1982). The two core attributes of Gaia in operation together at the first cellular stage of life would mean that at this stage the cell had a degree of control over both its interior components and its response to its external environment. This can be seen to mean that the first successful cell was a “Gaia”, using the core attribute definition. Therefore, from at least as early as LUCA to the present, every configuration of cells - first into biofilms, then into multicellular organisms and on up to the most modern and the largest – can be seen as a combination of smaller Gaias. This process can be seen to continue up to the level of the involvement of the whole biosphere. This gives us Gaia at planetary scale, the concept first presented to science by Lovelock (1972), some fifty years ago.