For some reason I assumed that aurochs was a Latin word. But, like everything else, the Latins stole it from somewhere else. In this case from northern Europe and Germanic speakers.
The word urus (/ˈjʊərəs/; plural uri)[7][8] is a Latin word, but was borrowed into Latin from Germanic (cf. Old English/Old High German ūr, Old Norse úr).[7] In German, OHG ūr was compounded with ohso "ox", giving ūrohso, which became early modern Aurochs. The modern form is Auerochs
Apparently these animals increased in size due to the extensive grasslands and the opportunity for grazing on large grassy plains. Conversely some of them shrunk in size when they were trapped on small islands like Sicily.
Aurochs were found to have lived on the island of Sicily, having migrated via a land bridge from Italy. After the disappearance of the land bridge, Sicilian aurochs evolved to be 20% smaller than their mainland relatives due to insular dwarfism
https://en.wikipedia.org/wiki/AurochsIf we look at the British isles we find many examples of smaller size animals related to islands. Eriskay ponies, Shetland ponies and sheepdogs for example although small versions of these animals are found all over Britain and elsewhere where they are needed.
What drives difference in size is due to a variety of circumstances. A bigger animal is more likely to be able to defend itself effectively. It is more likely to find a mate or mates and reproduce. We see this in the rutting season among the deer herds. The little ones may be nice but they do not get the ladies without a fight. We can observe this kind of behaviour on a Saturday night in most town centres.
But there are circumstances where small is better for survival.
Aurochs were found to have lived on the island of Sicily, having migrated via a land bridge from Italy. After the disappearance of the land bridge, Sicilian aurochs evolved to be 20% smaller than their mainland relatives due to insular dwarfism
https://en.wikipedia.org/wiki/AurochsThis process, and other "island genetics" artifacts, can occur not only on traditional islands, but also in other situations where an ecosystem is isolated from external resources and breeding. This can include caves, desert oases, isolated valleys and isolated mountains ("sky islands").
There are several proposed explanations for the mechanism which produces such dwarfism.
One is a selective process where only smaller animals trapped on the island survive, as food periodically declines to a borderline level. The smaller animals need fewer resources and smaller territories, and so are more likely to get past the break-point where population decline allows food sources to replenish enough for the survivors to flourish. Smaller size is also advantageous from a reproductive standpoint, as it entails shorter gestation periods and generation times.
https://en.wikipedia.org/wiki/Insular_dwarfismThe hunter gatherers had no choice but to hunt these animals. But a larger more sophisticated and settled society could invest time and resources into bringing these animals 'into the fold' and taming them. That saves the bother of hunting with all its risks.
What better than to create artificial 'islands' where the large beasts could be kept captive. Over a few generations they would decrease in size naturally. And if not the smaller ones could be selected to be bred while the larger ones would be dinner for a few weeks.
