Is macroevolution just accumulated microevolution?
Most biologists probably follow Darwin’s view that evolution proceeds through a long series of small changes each of which can occur readily - not through exceptional large-scale jumps; i.e. that macroevolutionary changes are effected through the successive accumulation of many small (microevolutionary) steps.
Indeed, for some, that macroevolution is reducible to accumulated microevolution is an a priori tenet of evolutionary doctrine. For example, here is Ernst Mayr, according to Gould the ‘prime architect of modern neo-Darwinism’ :
The proponents of the synthetic theory [of evolution] maintain that all evolution is due to the accumulation of small genetic changes, guided by natural selection, and that transspecifc evolution is nothing but an extrapolation and magnification of the events that take place within populations and species.
It is non-negotiable, because otherwise it would undermine evolution as an exclusively naturalistic theory.
However, we need to examine the evidence, which requires careful consideration of the different processes taking place in evolution (which all too often are conflated):
There are 3 key processes to evolution:
The production of genes (which provide genetic variability) - presumed to arise by essentially random (undirected) mutations.
The production of variations - by mixing the available genes in the course of reproduction - again, essentially random, though with limitations depending on e.g. the location of genes within the genome.
The selection of favourable gene combinations (those associated with favourable phenotypic variations) - which is not random, but probabilistic (statistical) based on generally enhanced survivability and reproducibility of individuals having favourable variations; i.e. this is natural selection.
The evolutionary position regarding microevolution and macroevolution can be summarised as follows:
Evolution is substantially true, so all 3 processes are ongoing, more-or-less simultaneously; successive instances of microevolution will accumulate and naturally lead to macroevolution, i.e. microevolution and macroevolution are a continuum.
It is generally thought that either a species changes gradually until it is sufficiently different (from some starting point) that it is considered a different species (anagenesis), or different populations of a species diverge gradually until they are sufficiently different from each other to be considered separate species (speciation). Either of these may involve segregation of existing genes and/or production of new ones - it does not matter which - so, again, macroevolution will emerge from successive accumulated microevolution.
There is ample evidence for (2) and (3) which are dependent on the existence of genes; so it is reckoned /presumed that (1) must also occur.
In addition, (1) and (2) are often conflated because both are random (and contrasted with non-random natural selection). Notably by the renowned evolutionist Ernst Mayr who frequently stressed that evolution entails 2 steps:
And, as there is ample evidence for (ii) this misleads many into thinking that there is also evidence for (i) - without considering the significant difference between (1) and (2) above.
random generation of variations (by mutation and genetic processes, he lumped them together), and
A key assumption of this widely accepted view of evolution - which treats evolution due to segregating genes and evolution requiring new genes as comparable - is that new genes will arise reasonably readily and frequently - at a rate that is comparable with the production of new variations by the mixing and segregation of existing genes. Yet it is clear - and not contested by proponents of evolution - that, although mutations are reasonably frequent (typically 1 in a billion per nucleotide per generation), the production of useful /constructive new genes (by mutation) is exceedingly rare.
So it is also clear that the evolutionary dictum that macroevolution is just accumulated microevolution is advocated for essentially ideological rather than empirical reasons.
And it is maintained by not looking too carefully at the scientific evidence - specifically by presenting evolution that is due to mixing and segregating existing genes as if it were evidence for the evolution of new genes.
 Stephen J. Gould, ‘Macroevolution’, in Encylopedia of Evolution Vol. 1, Oxford University Press, (2002) p E-25.
 E. Mayr, ‘Species and transspecifc evolution’, in Animal species and evolution, Cambridge, Massachusetts, (1963) p586.
 For example in E. Mayr, ‘Evolution’ in Scientific American, 239 (3) September 1978, p44. ‘Evolution through natural selection is (I repeat!) a two-step process. The first step is the production (through recombination, mutation and chance events) of genetic variability; the second is ordering of that variability by selection.’
Thumbnail - © PatríciaR - The file is licensed under the Creative Commons Attribution-Share Alike 3.0