today. Almost certainly, the isolation of 

 Jersey, which cut its population of deer off 

 from the deer on the mainland, set the 

 scene for the dwarfing process. Then, as 

 now, about fifteen miles of seaway would 

 have separated the island from France. 

 Red deer are good swimmers — they have 

 been known to cross four miles of open 

 water — but the greater distance from Jer- 

 sey to the mainland would have insured 

 their genetic isolation and allowed the 

 dwarfing process to commence. We know 

 from studies of fossil beaches and deep- 

 sea cores that the temperate episode lasted 

 about 1 1 ,000 years, and that for the central 

 6,000 years of this period, the sea was high 

 enough to isolate Jersey. This gives us a 

 maximum time span of just 6,000 years 

 for the evolution of the dwarf deer. 



In a paleontological context, 6,000 

 years is a very short interval. Red deer — of 

 normal, large size — have lived in Europe 

 for about the last 600,000 years, so the Jer- 

 sey dwarfing represents only one percent 

 of the species' duration. On a geological 

 time scale, the dwarfing process qualifies 

 as a very rapid evolutionary event. Biolog- 

 ically, however, 6,000 years represents 

 about 2,000 generations of deer — plenty 

 of time for the accumulation of genetic 

 changes leading to size reduction. To an 

 observer, this process probably would 

 have appeared as a gradual generation-to- 



generation transition. The perception of 

 evolutionary change as rapid or gradual is 

 therefore subjective and dependent on the 

 time scale. 



The tendency of large mammals inhab- 

 iting islands to become dwarfed has given 

 rise to much theorizing, but most re- 

 searchers agree that it is related to re- 

 stricted food supplies and the absence of 

 mammalian predators. In the limited land 

 area of an island, food is at a premium, and 

 small-bodied individuals that can make do 

 with less have a better chance of surviving 

 and reproducing. Small size would be a 

 particular advantage during times of win- 

 ter shortage, since island inhabitants can- 

 not migrate to richer feeding grounds, as 

 can their mainland counterparts. In addi- 

 tion, large carnivores are usually absent, as 

 small islands often cannot support the 

 numbers of herbivorous mammals that 

 predators need to exist. In the absence of 

 wolves, bears, or large cats, one of the 

 adaptive advantages of large size — de- 

 fense and escape from predators — disap- 

 pears. Also, in the absence of predators, 

 herbivore populations expand to the point 

 where individuals must compete for food, 

 adding to the premium on frugality and 

 small size. 



What became of the Jersey dwarfs? 

 About 1 15,000 years ago, the climate again 

 cooled as the last ice age began. Sea levels 



Red Jeer stags congregate on an estate in 

 northern England. Native to Eurasia, 

 modem red deer vary in size, but all are 

 larger and heavier, and the males have 

 more elaborately branching antlers, than 

 the Pleistocene dwarfs of Jersey. 



Leonard Lee Rue III; Bruce Coleman, Inc. 



dropped, Jersey once again was connected 

 to the mainland, and the dwarfs disap- 

 peared from the fossil record; all the later 

 remains of Jersey red deer are large. With 

 the reemergence of the bridge to the main- 

 land, the dwarfs would have come into 

 contact with normal-sized red deer. We do 

 not know if the dwarfs had, in 6,000 years, 

 become a separate species or even if they 

 were on their way to achieving their own 

 mating cues, which would ultimately have 

 isolated them genetically from mainland 

 deer. If they had not reached this point, 

 they may have been subsumed into the 

 population of mainland red deer by inter- 

 breeding. In either case, the dwarfs would 

 have had to compete with mainland red 

 deer and would have become easy prey for 

 large mainland carnivores. Adapted to is- 

 land life, the Jersey dwarfs perished when, 

 no longer isolated, they roamed into a new 

 land of relative giants. 



< 



o 



o 



3 



61 



