**3. Animal evolution<sup>2</sup>**

224 Biodiversity Loss in a Changing Planet

The presence of three early chapels and two incised stone crosses of early Christian style were recorded by the Rev. Kenneth Macaulay. 4, 5 The continued use of Norse place names, such as Oiseval – the east hill – and Ruaival – the red hill, and archaeological finds of Norse brooches and steatite, are strong evidence of continual occupation by the Norsemen and their descendents until the 20th century. However, prior to the steamship era, the inclement climate and the small exposed rocky harbour restricted access by visiting sailing vessels.

The inhabitants of St Kilda were predominantly of Celtic origin. The Vikings from Scandinavia occupied the Scottish islands until the 13th century. Control of the Hebrides was largely transferred from the Scandinavians to the Scots after the battle of Largs in 1263, but many settlers of Viking origin remained in the Hebrides. Studies of mitochondrial and Y chromosome DNA reveal that 30% of Orcadians and Shetland Islanders have Norse maternal and paternal ancestors, but in the Hebrides the male DNA remains around 30%, but Norse mitochondrial DNA falls to 8%, indicating that the Scandinavians took their women to the Northern Isles of Orkney and Shetland, but predominantly took local Celtic females as their partners in the Hebrides. 6 The degree of consent cannot be determined. There have been no specific studies of the DNA of the current single survivor and the descendents of the evacuees from St Kilda, but the persistence of Norse names suggests at

least some perhaps only male genetic biodiversity on St Kilda.

Fig. 5. Village bay

**2. Genetic origins** 

The islands of St Kilda were sufficiently isolated for animals to evolve different characteristics over a few centuries. The common house mouse probably introduced by the Vikings evolved into the now extinct, but larger subspecies of the St Kilda House Mouse (Mus musculus muralis), which was found only on St Kilda. The mouse was dependent on human habitation and died out after the evacuation in 1930.

Another local genetically different animal is the Soay sheep (*Ovis aries*). The name Soay derives from the Viking name of island of sheep. This breed is thought to be the descendents of the earliest domesticated sheep of Northern Europe, and is physically similar to the other wild ancestors of domestic sheep like the horned urial sheep of Central Asia and the Mediterranean mouflon. Soay sheep are hardy and extremely agile animals well adapted for survival on the high cliffs of St Kilda, though they are smaller than modern domesticated sheep. Unattended, their numbers tend to build up to peak, followed by a crash, perhaps due to over-grazing or parasite infection. In the autumn of 1960 for example, 1344 sheep were counted, yet by the following spring 820 had died.

They have a reduced genetic mechanism to select their coat colour compared to other sheep. Two genetic loci determine the colour which is limited to black, brown or, less commonly, white. The population of Soay sheep are a fascinating subject for researching evolution and

Limited Bio-Diversity and Other Defects of

without competitors or predators.

colour which is more pale grey and less rufous.

whose mother was a native of St Kilda.

of plants in the United Kingdom.

**4. Plant diversity2**

Fig. 8. St Kilda mouse

the Immune System in the Inhabitants of the Islands of St Kilda, Scotland 227

population dynamics, as the numbers are unmanaged, closed to migration in or out, and

The third different local sub-species is the St Kilda Wren, *Troglodytes troglodytes hirtensis*, which differs from the common mainland wren by its larger size, its long strong bill and its

Even the humans were rumoured to have evolved differently. The men over several centuries were hunter-gatherers of the birds and birds' eggs, which became their staple diet, from the sheer cliffs of St Kilda. They climbed barefoot and were said to have developed the 'St Kilda toe', an elongated big toe to give them more traction on the rocks. While this story is not substantiated, some tourists in 2008 were astonished by the size of the big toe of a man

St Kilda partially escaped the intense glaciations of the Great Ice Age, hence pre-glacial plants are found in its peaty soil. Two hundred varieties of lichen and a hundred and thirty different flowering plants have been discovered on the island. Some of these are extremely rare or ancient, such that a study of these plants helps to explain the distribution and origin

Fig. 6. Soay sheep

Fig. 7. St Kilda wren

population dynamics, as the numbers are unmanaged, closed to migration in or out, and without competitors or predators.

The third different local sub-species is the St Kilda Wren, *Troglodytes troglodytes hirtensis*, which differs from the common mainland wren by its larger size, its long strong bill and its colour which is more pale grey and less rufous.

Even the humans were rumoured to have evolved differently. The men over several centuries were hunter-gatherers of the birds and birds' eggs, which became their staple diet, from the sheer cliffs of St Kilda. They climbed barefoot and were said to have developed the 'St Kilda toe', an elongated big toe to give them more traction on the rocks. While this story is not substantiated, some tourists in 2008 were astonished by the size of the big toe of a man whose mother was a native of St Kilda.
