Despite the frequency with which the variable definitions of “evolution” are pointed out (eg Joshua Swamidass’s firm insistance that the correct scientific definition is only “change over time”) yet in common discourse about origins the mental concept nearly always reverts to “evolution by random variation and natural selection, as has stood the test of time for 160 years since Darwin.”
And so on the one hand, attempts from within the scientific community to extend or replace the modern synthesis tend to be regarded as “boiling down” to variation and natural selection anyway, selection being the key ingredient. At the other extreme, the critiques of evolutionary theory from inside or outside the Intelligent Design movement tend to focus their attacks on Neo-Darwinism, and to be regarded by their opponents, and maybe sometimes by themselves, as thereby being an attack on the whole concept of evolution (or according to some, an attack on the whole concept of science, or of knowledge, or of civilization itself – but let’s ignore the paranoics in this discussion).
Let me, at the risk of teaching grandmothers to suck eggs (my own grandmother never got the hang of that, for some reason…), propose my own hierarchy of definitions of evolution, to show … well, you’ll see as I go along. I’ll number them to enable shorthand reference later on.
- Evolution #1 – Change over time.
This definition is universally agreed, and entirely trivial. Virtually all Young Earth Creationists believe that the species have changed over time, either after the Fall or since the Flood.
- Evolution #2 – Descent with modification.
This too is nearly universally held, even by Creationists, albeit within the limits of “created kinds” in the latter case. It explains little on its own except life’s variety, but of course is axiomatic to genetic studies, which measure it directly. However, at the phylogenetic scale, it is not the only possible explanation of change over time – Richard Owen, for example – the very discoverer of homology – opposed descent with modification in favour of a theory of platonic-style forms and individual creation. Likewise Louis Agassiz. Their views can only be falsified by evidential demonstration of macro-evolutionary mechanisms, and then only by inference to best explanation. Owen and Agassiz’s outlook is, if one considers, a much more plausible explanation of the ubiquitous instances of convergence than are Darwinian mechanisms. Significantly, today’s expert on convergence, Simon Conway Morris, also invokes non-Darwinian process or processes unknown to explain it.
- Evolution #3 – Universal common descent.
Why so many are prepared to shed blood – usually that of others – over this principle is an interesting, but mainly sociological, question. Granted that there is sufficient similarity between living things to make it possible, there is still a good body of evidence against all life arising from just one organism, such as major differences in the chemistry of DNA replication and variation in the genetic code itself. And so the late Carl Woese, who discovered an entirely new kingdom of the Archaea, denied UCD and very reasonably proposed multiple origins of life, with a very long period of “horizontal” mixing before the arrival of LUCA (Last Universal Common Ancestor), the very existence of which Woese also seriously questioned (“it is not an entity, not a thing” – so not only no biological Adam, but no biological Noah, either!). Sociologically speaking, the insistence on UCD served to demonize special creationist fixism – and since that is no longer commonly believed, it is an obsolete tool in a tired trench-war left over mainly from Thomas Huxley’s naturalistic weaponisation of Darwin. Scientifically UCD is both an unnecessary, and a deeply anti-scientific, dogma. For life to have arisen only once in four billion years would demolish the foundational scientific principle of the uniformity of nature. That Louis Pasteur proved once and for all, in 1859, the non-existence of spontaneous generation means UCD runs against all evidence and all experience. Darwin himself, and the theistic scientists of the nineteenth century, concluded from this that life was, at first, specially created. Naturalists like Haeckel were forced by that very naturalism to say that spontaneous generation must have occurred, but only once. This puts the origin of life in precisely the same scientific category as the resurrection of Jesus: that is, a unique miracle. So Evolution #3, though so dogmatically held by naturalists, gives no support to naturalism: it only really supports special creation.
- Evolution #4 – Theories to account for Evolution #2.
It is only really here that any useful explanatory work can be done, by accounting for (a) the small-scale descent with modification that has been actually observed to occur, (b) unobserved instances of the same and (c) the grand history of life given the assumption that Evolution #2 is universal and, just as importantly, the sole significant process in play – there being, as the work of Agassiz showed within science and as all special creationists assert, alternative possibilities.
- Evolution #1 – Change over time.
Theories of evolution, then, need to be able to controvert these other possibilities at every level of life in order to claim to be fully persuasive.
You’ll notice that, unlike some writers, I haven’t made my Evolution #4 the Neo-Darwinian theory, nor have I even mentioned natural selection in my list. And that is because, if we’re talking about evolution in the current origins debate, ie that which has “stood the test of time over 160 years,” although this claim is true for my Evolutions #1 – #3 (with relatively trivial consequences), it is true of no particular theory of evolution, and specifically it is not true of natural selection, which has suffered serious setbacks every time it has been tabled as an option, and which is currently in just such a beleagured state, as a sufficient explanation for the nature of living things.
But my space having been filled, I’ll leave that historical discussion to another post.