Students of history and of biology share a common delight: as they study the details of any subject, they find a fascinating diversity of cases which far exceeds any preconceived expectations. But that is not their sole delight. Some will also see unifying themes therein, with coincidences that beg for explanation and leitmotifs which please the aesthete. Some scholars choose to stress the diversity, perhaps even the perversity, to be found in events in history (or, in biology, of living forms). Other scholars may feel happier following the motto e pluribus unum.
There is no right or wrong to it, that one is a unifier and another a divider of forms. We ascribe these differences in scientific or philosophical temperament to individual style or taste: some like a tidy story and others prefer a wealth of detail. Nor is this a matter of respect or lack of it for detailed facts. A grand unifier may study facts painstakingly while trying to unify (perhaps bending the facts, or perhaps ruefully admitting failure) while the person with a predilection for detail may believe in it only in principle, leaving it to others to dig them up and record them. Those who grant that details are important may do so either to prove that they fit into a grand scheme or to disprove that very point.
This difference is, perhaps not unsurprisingly, more than a matter of style. It is also an issue of substance in the nineteenth century, both in history and in biology. It became a topical question whether there is meaning in unfolding events: whether history exhibits fundamental