Scientists – well, palaeontologists at least! – can and do disagree on many things. One thing they do tend to agree on is that it’s nice if you can be the first person to discover or identify a new species. This has led to a trend where some biologists, botanists and palaeontologists can see differences, often very subtle ones, which they use to justify the setting up of a brand new species. This has resulted in (and is recorded in the extensive literature) an increase in the numbers of different species based on smaller and smaller differences. These scientists are known as “splitters”. Other scientists object because they say that perceived differences may not, in fact, be differences at all, or they are caused by something other than the occurrence of a brand new species. They contend that the differences are due to variations in morphology (body shape) caused by environmental factors and tend to “lump” specimens that show minor differences into the same taxonomic unit. Both approaches have their advantages and disadvantages when it comes to biostratigraphy and its applications.

A crude analogy might be the body shape of humans adapting to a hot, dry climate (tall and thin like African plains dwellers) or to cold climates (shorter and rounder like the Arctic Inuit) with a whole plethora of forms in between. Where does one draw the boundaries (if any)? What about clear anomalies to this hypothesis (the presence of short body forms – so-called “pygmies” – in Africa)? One reason why the human species should not and cannot be “split” into different species is that we know that everyone on the planet belongs to a single species. We know this for one readily observable reason; we can all breed together. A species is defined in the biological sense because of its ability to reproduce viable young. If you cannot breed then you are not of that species – it’s as simple as that. Medical problems and personal preferences notwithstanding, any individual male human on Earth can successfully genetically breed with any individual female human.

[“Interesting” sidenote: the subspecies was invented to account for members of a species who could genetically interbreed with others, but do not do so due to inhibitions put in place by other factors, such as a mountain being in the way for example (!). The Eastern Gorilla (Gorilla beringei) has two subspecies (Gorilla beringei beringei and Gorilla beringei graueri). In simple terms, the first subspecies lives up a mountain, the second in lowland forest. The two populations seldom, if ever, meet and therefore they do not interbreed although it is physically and genetically possible for them to do so. Eventually, one assumes, the two will drift apart genetically so that eventually they will not be able to interbreed at all and two new, fully genetically distinct species will have arisen.]

The problem with extinct organisms is that we simply do not know with whom they bred, as it can never be observed. We have to assume that those fossils that look the same were the same species and therefore interbred. The argument between splitters and lumpers is about just how far can we take any differences within and between groups of specimens and attribute them to being separate species, or simply just variations in shape/size in a normal population. The debate can never be resolved using current methods. Biostratigraphy, like other sciences, follows “fashionable trends”. Currently the use of the subspecies (and the subgenus) is falling or has fallen out of favour, but such “splitting” approaches were popular in the 1970s and 80s which spans a great deal of exploration & production activity and consequent biostratigraphic study.

It is the goal of biostratigraphers to establish documentation of stable morphological variations that have stratigraphic and/or paleoenvironmental value. In effect, simply to “label” forms we find useful. This is not necessarily how a biologist would approach the subject!