turn the question "how complex is this system?" into a question that's only answerable by making reference to what the system is made out of. This might not be a fatal issue per se, but it suggests that measuring complexity is an insurmountably relativist project—after all, how are we to know exactly which parts we ought to count to define the complexity of a system? Why, that is, did we choose to measure the complexity of the human organism by the number of genes we have? Why not cells (in which case the blue whale would beat us handily), or even atoms (in which case even the smallest star would be orders of magnitude more complex than even the most corpulent human)? Relatedly, how are we to make comparisons across what (intuitively) seem like different kinds of systems? If we've identified the gene as the relevant unit for living things, for instance, how can we say something like "humans are more complex than cast-iron skillets, but less complex than global economies?"
Even if we waive that problem, though, the situation doesn't look too good for the mereological size measure. While it's certainly true that a human being has more nucleotide base pairs in his DNA than a yeast microbe, it's also true that we have far fewer base pairs than most amphibians, and fewer still than many members of the plant kingdom (which tend to have strikingly long genomes). That's a big problem, assuming we want to count ourselves as more
- Whether or not these comparisons are accurate is another matter entirely. That is, whether you think it's actually true to say that humans are less complex than the 21st century global economy, it seems clear that the comparison is at least sensible. Or, at least, it seems clear that it ought to be sensible if we're to succeed in our goal of finding a notion of "complexity" that is widely-applicable enough to be useful. I'll argue in 2.2 that there is sense to the comparison and (moreover) that the global economy is more complex than an individual human. For now, though, it's enough to point out that even having that discussion presupposes a wide notion of complexity that renders the mereological size measure suspect.
- Most amphibians have between 109 and 1011 base-pairs. Psilotum nudum, a member of the fern family, has even more: something on the order of 2.5 x 1011 base-pairs. The latter case is perhaps the most striking comparison, since P. nudum is quite primitive, even compared to other ferns (which are among the oldest plants still around): it lacks leaves, flowers, and fruit. It closely resembles plants from the Silurian epoch (~443 million years ago – 416 million years ago), which are among the oldest vascular plants we've found in the fossil record.