The Holocene Calm after the storm

The ice sheets had retreated and the sea levels had attained their present limits about 10,000 years ago. A thousand years later, the world had warmed to perhaps a slightly higher degree than it is at present. The Asian summer monsoon intensified, while global precipitation reached a new peak in recent times. Forests expanded in the tropical belt. This was the "Holocene Optimum," a period of warmth and high rainfall.

Loxodonta and Elephas were left as the sole elephant inheritors of the African and the Asian continents, respectively. A few woolly mammoths may have still roamed the Siberian wastes, while some were certainly stranded on Wrangel Island, destined to reduce in size with succeeding generations. Relict dwarf elephants also possibly remained on some Mediterranean islands. It was of no consequence. Their fates were already sealed.

During the Pleistocene, Loxodonta were literally in hiding in the moist forests of Central Africa, as their cousins from the genus Elephas roamed over the drier regions, which were far more extensive in the continent. The warming and wetter trend, which set in after the last glaciation about 18,000 years ago, contributed to the expansion of woodlands in Africa, a process that continued into the early Holocene, when peak warmth and precipitation was reached. Although evolutionary rates had been slow in Loxodonta, the very traits that were more suited for a life of browsing in forests may have favored their dispersal out of the moist forests into the expanding woodlands.

It is not known how and why Elephas disappeared from Africa. In any case, at some point in time, the late Pleistocene climatic and habitat conditions conferred on an earlier form of modern Loxodonta a selective advantage over Elephas (a late stage of recki or iolensis), thereby enabling it to become the sole proboscidean inhabitant of the African continent.

Loxodonta spread throughout the continent, with the exception of the central Saharan region, by the dawn of human history. When the earliest Egyptian dynasties were established 5,000 years ago, the African elephant was found in the lower Nile region, as well as throughout coastal North Africa bordering the Mediterranean. This original range of over 40 million km2 has since shrunk to about 5.8 million km . Two subspecies of the African elephant were recognized until recently (the smaller forest elephant, Loxodonta africana cyclotis, and the larger bush or savanna elephant, Loxodonta africana africana), but a case has now been made for treating them as distinct species (see section 1.9.4).

There is no precise date for the origin of Elephas maximus in Asia as the fossil record for this species is virtually nonexistent. All that is known is that the modern Asian elephant was derived during the later Pleistocene from E. hysudricus found in the Siwaliks of the Indian subcontinent. Since the last glaciation, the southern and eastern Asian region, covering the historical range of Elephas maximus, also came under the influence of a warmer, moister climate when forests expanded. Unlike its African cousin, the Asian elephant had an evolutionary history of adapting to a coarse, grazing diet characteristic of more arid habitats. How the species coped with the reversed trend in habitat is not clear.

By the mid-Holocene, about 5,000 years ago, another period of aridity set in over South Asia and possibly a wider region. Desert appeared in the northwest of the subcontinent, while the great Indus River valley civilization, which may have been the first to tame the Asian elephant, declined by 4,000 years ago. The stable isotope investigations of southern Indian peat deposits by my research group clearly show that arid conditions were established here around the same time.

About 4,000 years ago, the Asian elephant ranged from Mesopotamia in the west through a narrow belt along the Iranian coast into the Indian subcontinent and further east into Southeast Asia and China at least as far north as the Yangtze-Kiang. This earlier range of over 9 million km has shrunk to less than 500,000 km2 at present. Three subspecies of the Asian elephant have been commonly described: Elephas maximus maximus from Sri Lanka, E. m. indicus from the Asian mainland, and E. m. sumatranus from the island of Sumatra. The basis for this differentiation, however, is less clear than it is for Loxodonta.

Today, the Asian elephant is thought of as a creature of the forest and the African elephant as one of the savanna. This is misleading for several reasons. If the actual distribution of Asian elephants is considered, then it is true that most of their range is forested habitat. However, this may simply be due to the occupation of the drier habitats by humans and not a reflection of their favored habitat. Similarly, large populations of African elephant are still found in woodlands and moist forests. Evolutionary history and dental characters suggest that Elephas maximus is more adapted to a grazing diet than are Loxodonta. When the feeding habits of the two genera are compared, there is little to differentiate between them in the degree of browsing versus grazing (see chapter 5). African forest elephants and Asian elephants in moist forests are almost entirely browsers. African savanna elephants and Asian elephants in deciduous woodlands include almost identical proportions of grass in their diets, as seen from carbon isotopic analysis of bone collagen and from direct observations. In spite of differences in evolutionary adaptations, the two species inhabit a variety of habitats, from semiarid savanna to moist forests, where they show similar feeding behavior.

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