Measurements of individuality
Williams (1956) approached biochemical individuality in an interesting way. He examined whether it was possible for a single uniform drug dose to be prescribed for the whole human population, and concluded it could not be. Williams assumed that any individual trait could be considered to be normal if it lay within 95 % (probability = 0·95) of the distribution around the mean. The probability that an individual is normal for two traits is 0·952. For 100 traits, the probability of normality of any individual for all traits is 0·005, and for 1000 different traits it is vanishingly small. Ergo, we are all deviant in certain characteristics.
There are at least 15 distinguishable environmental signals [water, five (or six) primary minerals, light, gravity, soil structure, neighbour competition, herbivory, disease, allelopathy, wind, gases; Trewavas, 2000] to which individual plants are sensitive, many observable traits that can be distinguished, and there may be as many as the number of distinguishable genes. On that basis, it is likely that every individual plant, at least in the wild, is unique in one or more traits.
Williams (1956) also describes anatomical and biochemical individuality in normal reproducing human beings, and lists the variations that he could find in the literature for apparently normal healthy, reproducing, human beings. The variations described are enormous given the necessity for producing such a complex organism. It would be useful if an equivalent catalogue of plant variation could be compiled, if that is possible. However, the modular character to plant growth and development and plasticity might make this a difficult task.
But the biochemical observations measuring variations in vital constituents could equally apply to plants, although I have never seen them compiled. No doubt, metabolite profiling will indicate this in greater detail. The Handbook of biological data does contain some information about plants, showing variation in dry weights, protein, secondary metabolites, ions and other metabolites. Elsasser (1988) regarded the data compiled by Williams (1958) to represent the primary difficulty in the instructionist view of life that regards the genome as merely a computer tape (full of information) and the cell as a computer following instructions that should then always result in exact replicas (clones) of the genome. Thus organisms survive perfectly well despite huge variations in constituents, and the notion of being simply complex machines (which require precision and reproducibility in structure and composition) is untenable.