Biological Anthropology.

Lab Report: The Evolution of Elephant Tusks

Introduction:

This report will discuss the evolutionary adaptation of African Elephants to the pressure of ivory poaching. Ivory poaching is an unregulated and illegal practice wherein poachers kill elephants and harvest their tusks. Tusks are specialized, elongated teeth which are used for a variety of purposes by elephants, including but not limited to: stripping bark from trees, digging, and (especially in the case of males) fighting. Males use their tusks in contests associated with reproduction, fighting other males for mating rights. These tusks are made up of a material known as ivory, which is traditionally carved into various luxury goods from piano keys to bracelets. Ivory is primarily dentin, a mineralized collagen fiber composite material (Albéric, 2018). Certain other animals such as hippos and narwhals are also possessed of ivory, though elephant ivory is by far the most valuable variety(Britannica, 2022) While the international trade of elephant ivory is widely regarded as both abhorrent and illegal, the practice continues to this day. 

A period of particularly intense ivory poaching existed in Mozambique from 1977-1992 as a result of a civil war. During this war, over 90% of the elephant population in Gorongosa was killed and their tusks harvested. This ivory was then sold and the proceeds spent on war materiel. This ruthless reaping of ivory represented a significant selective factor in the elephant population. Around 6% of the female elephant population in Gorongosa at the beginning of the war was tuskless, being born without the capacity to grow tusks. By the end of the war, this percentage had more than tripled (Poole, 2016).  

I hypothesize that as poaching increases, the frequency of tuskless elephants will increase.

Methods:

The African bush elephant (Loxodonta africana) is the largest terrestrial animal. Adults of the species stand between 7 and 13 feet tall, and weigh between 4,500 and 13,500 pounds. Adult males and females typically have curved tusks, which can reach 11 feet in length. They have large triangular ears and very tough gray skin (Howard, 2017).  Some elephants are born without the capacity to grow tusks, which is highly relevant to the content of this report.

In order to efficiently measure the population of this species, which lives in herds and ranges across vast areas of land, a census must be conducted by air. This involves cameras placed at the sides of small aircraft, which are then flown at a fixed height (in this case 300 feet.) Observers within the aircraft then count elephants seen within a strip of land with a fixed width and trigger the cameras to document each sighting. The total area measured and the total elephants counted can then be calculated as a population density and extrapolated to the rest of the elephants’ habitat range. This renders a total population count for African bush elephants.

To determine the frequency of tusklessness, rigorous observations must be made. In order to gather these observations, photographs of around 10,000 African bush elephants from 15 separate and widely distributed populations were inspected. In the course of these inspections, sex and status of tusks were established. Figures on the frequency of tusklessness were thereby gained, and cross-referenced with the frequency of poaching in the area from which each population hailed (Steenkamp, 2007). 

Results:

A 2015 study published by the Canadian Center of Science and Education shows a clear motivation for poaching in Zambia: ivory. Between 2007 and 2013, there were 129 elephants illegally killed in North Luangwa Valley in eastern Zambia. Of these, over half were killed only for their tusks. An additional fifth were killed for both meat and tusks, with another fifth killed either for meat or simply killed and left to rot (Nyirenda, 2015).

This data exposes a significant evolutionary pressure affecting African bush elephants: Ivory poaching.

 Steenkamp et al showed the consequences of this pressure in their 2007 study on the incidence of tusklessness in populations of African elephants. This study showed a substantial link between the frequency of tusklessness and the pressure of ivory poaching. When controlled for fractured tusks, incidences of tusklessness rose sharply in areas under pressure from poaching.  (Steenkamp, 2007)

As can be seen in this chart, derived from the findings of Steenkamp et al, high levels of poaching coincides with a high frequency of tusklessness. 

Additional study conducted in Gorongosa National Park in Mozambique reveals a similar trend, albeit in a single region. As mentioned in the introduction of this report, the elephants of Gorongosa were drastically affected by the nation’s civil war from 1977 to 1992. The generation of elephants which lived through the civil war displayed tusklessness in about 50% of the female population, and the following generation displayed tusklessness at a rate of about 33%. This further confirms the link between tusklessness and poaching, as well as the heritable nature of tusklessness. Females displaying tusklessness gave birth to young who also displayed the trait, and the overall percentage of tusklessness fell when the pressure of poaching had been removed. (Poole, 2016)

Conclusion:

The research summarized in this report supports my hypothesis that as poaching increases, the frequency of tuskless elephants will increase. The pressure of Ivory poaching can be established by information found in Nyirenda et al, where over half of the illegally killed elephants included in the study were killed for tusks alone. Data derived from Steenkamp et al shows that elephant populations under pressure from poaching display tusklessness at a higher rate than populations with minimal human contact; this establishes a higher degree of Darwinian fitness among tuskless elephants under the condition of frequent ivory poaching. The results of Poole’s ongoing study in Gororngosa National Park establish both the heritability of tusklessness as a trait and the adaptive nature of the trait. When the pressure of  poaching was removed, the percentage of female elephants displaying the trait fell in the following generation.

Discussion:

Ivory poaching is a terrible practice which unfortunately persists to this day. Elephants are selectively killed, their tusks harvested for unnecessary and expensive objets d’art. This places enormous pressure on an elephant herd, as members of their population are senselessly killed. Elephants are highly intelligent, emotionally-complicated animals and it is entirely possible that the loss of a herd mate may have lasting repercussions for the herd. One such repercussion, as shown here, takes place through natural selection. As elephants with tusks are selected by poachers for harvesting, the normally-small population of tuskless animals are left to constitute a far higher percentage of the population. This represents differential survival, as individuals without tusks are more likely to survive and have more offspring than those with tusks. This is a key aspect of natural selection, the tuskless elephants have a higher degree of Darwinian fitness than their tusked peers when under the pressure of poaching. 

Without thorough knowledge of the impacts of poaching on elephant populations, it is more difficult to alleviate the worst effects and help these noble animals survive in a rapidly changing and often harsh world. Such knowledge can only be gained through the scientific method, as was done in the studies summarized here. Observing and documenting the trend of elephants killed for tusks alone, charting the progress of a population recovering from devastation via ivory poaching, providing evidence for the link between tusklessness and poaching, these were all achieved through rigorous application of the scientific method.

This is a clear example of evolution being forced upon a species by human activity. Like the peppered moths of the industrial revolution, these elephants have adapted to the pressure of sharing a planet with humanity. As a result, they have lost a valuable tool which served them well for millenia. And the effects don’t end there. According to Shannon et al, orphaned elephants may display social and behavioral consequences decades after losing their parents (Shannon, 2013). Additional effects may include a permanent loss of important information in a herd, such as navigational and seasonal knowledge passed from parents to offspring for centuries.

Poaching is a hard problem to solve. Overhead surveillance of herds, while costly, can be an effective method for detecting and possibly preventing the poaching of elephants. Gun control represents another option for governments attempting to curb poaching in their nations, removing the tools used by criminals to kill their prey. A dramatic cultural change could also hold great promise in stopping poaching: ubiquitous disgust for ivory. Ivory itself holds little intrinsic value, as plastic and resin supplanted the advantage of its material properties decades ago. It is only the prestige and exclusivity of ivory which represents value to humans, and by overshadowing these perceived benefits with a universal disdain we may eliminate the market for ivory altogether.

References:

Albéric, Marie & Gourrier, Aurelien & Wagermaier, Wolfgang & Fratzl, Peter & Reiche, Ina. (2018). The three-dimensional arrangement of the mineralized collagen fibers in elephant ivory and its relation to mechanical and optical properties. Acta biomaterialia. 72. 10.1016/j.actbio.2018.02.016.

Poole, Joyce. (2016) Selection for Tuskless Elephants. HHMI BioInteractive Video. https://www.youtube.com/watch?v=IxJDUrDH9v4 

Britannica, T. Editors of Encyclopaedia (2022, May 23). ivory. Encyclopedia Britannica. https://www.britannica.com/topic/ivory

Howard, M. 2017. "Loxodonta africana" (On-line), Animal Diversity Web. Accessed October 05, 2022 at https://animaldiversity.org/accounts/Loxodonta_africana/

Nyirenda, Vincent & lindsay, & phiri, & stevenson, & chomba, & Namukonde, Ngawo & Myburgh, Willem & Reilly, Brian. (2015). Trends in Illegal Killing of African Elephants (Loxodonta africana) in the Luangwa and Zambezi Ecosystems of Zambia. Environment and Natural Resources Research. 5. 24-36. 10.5539/enrr.v5n2p24. 

Steenkamp G, Ferreira S M, Bester M N, Tusklessness and tusk fractures in free-ranging African  savanna elephants  (Loxodonta  africana). Journal  of  the  South  African  Veterinary Association (2007) 78(2): 75–80 (En.). Mammal Research Institute, University of Pretoria, Pretoria, 0002 South Africa.

Shannon, G., Slotow, R., Durant, S.M. et al. Effects of social disruption in elephants persist decades after culling. Front Zool 10, 62 (2013). https://doi.org/10.1186/1742-9994-10-62