Elephant Evolution

Darwinian evolution, alluded to in the previous chapter, is seen in contemporary biology in complex and sometimes conflicting terms. We subscribe by and large to the views on evolution as developed by Richard Dawkins in both The Selfish Gene (1989) and The Extended Phenotype (1999). Our approach, although predicated upon the following discussion of how Dawkins might view evolution, will in many cases point only to a simplified conception of how crucial characteristics of elephant behavior might have evolved, without entering into the complexities of how or perhaps even whether, in fact, this may have taken place.

Dawkins (1989) holds that “the fundamental unit of selection, and therefore of self interest, is not the species, nor the group, nor even, strictly, the individual. It is the gene, the unit of heredity” (p. 11). Dawkins sees natural selection leading to stable forms of life with high longevity, fecundity, and copying fidelity coded within the DNA of the individual (see pp. 18–23, 41). Given that life begins with the gene, aggregating into what are referred to as phenotypes and residing in a transfer mechanism he describes as a replicator, Dawkins (2008) does not neglect nor deny the existence of complex individual organisms. He sees the organism as a physically discrete machine, with essential internal organization. It is a definable unit, with a unique collection of the same genes. Yet, it is different from all other organisms. It has its own coordinated central nervous system such that “all its limbs conspire harmoniously together to achieve one end at a time” resulting in “intricate orchestration, with high spatial and temporal precision, of the hundreds of muscles in the individual” (pp. 250–251).

Copying errors will occur, resources will be stressed, and competition can delete the less favored, but nothing controls the process. “Trivial tiny influences on survival probability can have a major impact on evolution. This is because of the enormous time available for such influences to make themselves felt” (Dawkins, 1989, p. 4).

Evolution does not act for the good of the species but for the survival of the individual (perhaps “selfish”) gene. Yet these self-preserving, genetically inherited traits under certain circumstances might serve to promote that society. For this to happen, Dawkins claims “that we shall be faced with something puzzling, something that needs explaining” (p. 4). The male may be banished from the group and be forced to compete and distribute his selfish genes among many different groups. These groups, guided by a single female who occupies her position not through conflict but by an approximation to acclimation, not only nurtures her young for a long period of time but retains a high proportion of her female offspring within a single group for their entire extended lifetime. Perhaps this is the unusual circumstance that is needed for the selfish gene to contribute or be displaced in order that the species survives?

A significant part of the content of the pages that follow documents how elephants might be the unique species of animal that most closely meets the unusual circumstances demanded by an evolutionary mechanism centered upon the propagation of genes.

Proboscideans, the ancestors of today’s elephants, can be traced back in time for more than 35 million years (Figure 2.1). They evolved in dense, closed-canopy forests. By the time that Elephantidae in the form of the mammoth and present-day Asian (Elephas maximus), African savanna (Loxodonta africana), and forest (Loxodonta cyclotis) elephants emerged as distinct species, the forests had receded, giving way to savannas. Because of this evolution within a forest, elephants emerged onto the open savannas with capabilities formed in the forests. Their sense of hearing and smell had evolved in favor of sight. Elephants were thus capable of both emitting and detecting calls over the widest range of frequencies of any animal. Their eyesight was poor, adjusted more to the restrictions of dense vegetation than to the vistas of the savannas.

Dawkins (1989, p. 7) relates a story told by Colin Turnbull who took a pygmy friend, Kenge, out of the forest for the first time in his life. They climbed a mountain and had an extended view over the plains where in the far distance a herd of buffalo were grazing. Kenge turned to Turnbull and asked, “What insects are those?” Puzzled by the question, it took Turnbull a moment to realize that in the limited vision of the forest there was no need to adjust for distance when judging size. Without any experience of using known objects as a basis for comparison, Kenge was unable to interpret the size of what he saw.

The vertical structure of temperature, moisture, and wind in the forest favored long-range transmission of low-frequency sounds with wavelengths on the order of meters to tens of meters rather than centimeters. Trees and vegetation have little attenuating affect on sounds with such long wavelengths. Wind speed and turbulence, which effectively destroy sound and limit the distance over which sound travels, are low to nonexistent in the forest. Temperatures at the cool floor of the forest are, especially during the day, much lower than at the sunlit forest canopy, resulting in an increase in temperature from the floor to the tops of the trees. This phenomenon, called a temperature inversion, results in denser air (lower temperatures) at the surface and less dense air (higher temperatures) at the tops of the trees. Sound waves produced at the surface in such a layer of air are bent first upward and then downward as their speed changes with lower and higher temperatures. The sound wave effectively bounces down this inversion channel. This ducting of sound allows the calls of elephants to be heard by other elephants at distances of kilometers. A similar temperature gradient is present in the world’s oceans, where it is known as the SOFAR channel or thermocline and is used by marine mammals such as whales to send signals to conspecifics thousands of kilometers away. The utility of this ability to communicate over vast distances can be measured not only in terms of finding mates but of being able to use food resources separated by many hundreds of miles of barren ocean. The ability not only to know where food is but to have unobstructed access to these locations is something that terrestrial animals are being progressively denied as their habitats shrink and migration routes are severed.

In a rather surprising twist of fate, the dry savannas that most of the elephants now found themselves occupying exhibit a powerful night-to-day reversal in acoustic conditions. Cloud-free, dry atmospheres of the savannas allow the daytime heat gained through absorption of solar radiation to stream upward and outward to space as soon as the solar angle drops toward sunset. The loss of outgoing longwave or terrestrial radiation operates to rapidly cool the earth’s surface. Surface temperatures that may have approached 45–50 °C (113–122 °F) in the middle of the day and early afternoon now drop precipitously to 10 °C (50 °F) or lower, producing a daily range in temperature of some 40 °C (72 °F), more than many locations on earth experience from the hottest summer day to the coldest winter night. A very strong and shallow nocturnal inversion is formed, allowing loud elephant calls to be heard by another elephant as much as 10 km (6 mile) away. This ability to communicate over such great distances translates to being heard over an area of greater than 300 km2 (112 mile2). Such a reach in communication is crucial to elephant reproduction, predator avoidance, and resource utilization, all factors that we examine in terms of their behavior, social structure, and cognition (Garstang et al., 1995, 2005; Larom et al., 1997).

Conversely, during the day when surface...