Cyanophora paradoxa is an elegant alga, a single-celled cousin of plants like oaks and roses, which glides through its freshwater environment, bearing a pleasant green hue due to its photosynthetic chloroplasts. Genomic analysis of C. paradoxa shows that the combination of an ancient C. elegans ancestor, bacteria, and primitive photosynthetic cyanobacteria gave rise to plants as we know them today. Animals and plants are eukaryotes, organisms that have cells which contain discrete “organelles” that carry out certain functions. These organelles – most notably chloroplasts and mitochondria – look suspiciously like atrophied microorganisms of their own, both structurally and genetically. They even contain their own DNA, separate from the cell’s DNA in the nucleus.
Genetic studies of the tiny C. paradoxa show that the alga shares genes with cyanobacteria — which are free-living photosynthetic bacteria – and also with other bacteria that contribute genes that allow food products to be transferred from the chloroplast to the C. paradoxa cell. The picture that emerges is of a union between ancient eukaryotes, cyanobacteria, and the transferring bacteria, which produced a new tripartite symbiotic entity which thrived on the cooperative activity of all three working together. Estimates put the date of this union at some 1.6 billion years ago. In the long stretch of time since then, the symbiosis has deteriorated to the point that the cyanobacteria are no longer separate organisms, but have become the functional organelles that are a natural part of C. paradoxa and its plant cousins.
As the article linked here notes, this history gives plants – indeed all higher organisms, given that animals share such apparently symbiotically-derived organelles as well – the appearance of being “cobbled together.” Their seemingly accidental history of construction seems to give credence to the reductionist view of life. Indeed, it makes life seem to be accidental in the old, philosophical sense of the term – a congeries of parts that have randomly become jumbled together, without an intrinsic unity. There is evidence that the origin of complex life was in the conjunction of two disparate entities in the past; does this not reveal that what seem to be single entities today, derived from those ancient biological collisions, is just a mechanical collection of parts? Does this parts-first historical analysis trump any other in the consideration of life?
I submit that the mistake is to unquestioningly give the scientific analysis precedence over others. Science is reductionist – that is its glory, and its danger. Scientists delight in revealing aspects of nature that aren’t apparent to the common-sense, everyday experience of nature. Seemingly solid objects are composed of atoms that are mostly space. The pressure you feel on touching a hard surface is created by, at the microscopic level, not a solid surface at all, but the repulsion of electromagnetic fields. There is a biological code that is shared by you, bears, and bananas. It is not the Sun that rises and sets, but the ground beneath you that spins. Science unveils a hidden dimension present just beyond our senses.
Yet it does not follow from this that the evidence of our senses and our reason is to be abandoned to the analysis of science. If science looks at the trees, we may not say that there is no forest. If a desk is built of atoms that are mostly empty space, a desk is not mostly empty space – it is a desk. If an organism is built by the combination of two organisms in the primordial seas, it is not now necessarily just an amalgam – it has become a distinct plant or animal.
A billion years ago, it seems, a photosynthetic bacterium was absorbed by a primitive eukaryote. Along with the help of some passer-by bacteria, this meeting, through mysterious steps lost in the distance of time, led to algae and plants as we know them today. And yet anyone stepping outside, or even using a microscope, sees a plant not as a colony of disparate forms, but as a functional, coherent unity. The boundaries of this unity – both physical and, as the investigation of evolutionary history shows, temporal – can be challenging to elucidate. The particulars of change and of distinction have always been challenging to philosophy and to science. It is hard to point to the moment when the line was crossed between symbiosis and unity, but this does not change the fact that what is foremost today is unity. This structure may have begun as a union of two beings; today it is clearly just one being. We must not let the complexities of history or of reductionist analysis swamp the evidence of sense and unity visible today. The truth lies in the synthesis of all evidence, not in the dominance of just one line.
