How Elephants got their trunks

How Elephants got their trunks
This report discusses the evolution of the Elephant. The fossil evidence is described and the theories of Evolution known as Lamarckism and Darwinism are compared and evaluated. Neo-Darwinism and punctuated equilibrium are also defined.
Introduction
Curiously, the evolution of the Elephant was considered by the 3rd American President, Thomas Jefferson. During his presidency the remains of a Mammoth were excavated and brought to his attention. The historical context of this is intriguing. In 1804 in France, Georges Cuvier proposed the radical idea of “ Extinction” after examining fossils. However, most Europeans and Americans were not ready for this concept; preferring instead that all species were saved by Noah on his ark. Consequently, Thomas Jefferson organised an expedition “Way out West” in 1804 to find the Mammoth which must obviously be alive somewhere. Nowadays, that wouldn’t happen and the word “extinct” is very familiar.

Lamarckism compared to Darwinism
Jean-Baptiste Lamarck (1744-1829) and Charles Darwin (1809-1882) were both interested in the diversity of life and speciation. Lamarck is known for his Theory of Inheritance of Acquired Characteristics, first presented in 1801. If an organism changed during life in order to adapt to its environment, those changes would be inherited by offspring. Lamarck believed that elephants all used to have short trunks. When there was no food or water that they could reach with their short trunks, they stretched their trunks to reach the water and branches, and their offspring inherited long trunks. Lamarck also said that body parts that are not being used, such as the human appendix and little finger would gradually disappear. Eventually, people will be born without these parts. Lamarck also believed that evolution happens according to a predetermined plan and that the results have already been decided.

Darwin’s book dealing with evolution appeared in 1859 almost 60 years after Lamarck. Darwin believed that changes in an organism during its life do not affect the evolution of the species. He observed that organisms, even of the same species, have many variations that help them to survive and have more offspring. The offspring are born with their parents' helpful traits, and as they reproduce, individuals with that trait make up more of the population. Other members of the group that are not so well adapted will not survive. This is referred to as “Natural Selection”. According to Darwin, an early population of Elephants would have slight variations in trunk length. When there was no food or water that they could reach with their short trunks, the ones with short trunks died off, and the ones with long trunks survived and reproduced. Eventually, as the survival benefit of having a long trunk paid off then all of the elephants developed the long trunks. Darwin also believed that evolution does not happen according to any sort of plan.

Darwin's theory of “Natural Selection” has been supported by a considerable body of evidence. Lamarck's Theory of Inheritance of Acquired Characteristics has been disproved. For example if an elephant’s trunk is damaged or cut short its offspring will still be born with long trunks; this contradicts Lamarckism. On the other hand, the bacteria responsible for Tuberculosis (Mycobacterium tuberculosis) reproduce quickly. Some strains have evolved resistance to all forms of antibiotic through a process of natural selection. There are now strains of multi-drug-resistant Tuberculosis posing a worldwide health risk to humans.
Neo-Darwinism and punctuated equilibrium
As part of the disagreement about whether natural selection alone was sufficient to explain speciation, the term Neo-Darwinism was introduced to refer to the version of evolution advocated by Alfred Russel Wallace and August Weismann with its heavy dependence on natural selection. A complete rejection of Lamarckism came from Weismann's “ gamete theory”. Weismann realised that the cells that produce the gametes (such as sperm and egg in animals), separate from the somatic cells that go on to make other body tissues at an early stage in development. Since he could see no obvious means of communication between the two he asserted that the inheritance of acquired characteristics was therefore impossible; a conclusion now known as Weismann's barrier.
These days Neo-Darwinism is further supported by an understanding of Genetics. The genes passed on to the offspring will bear the code to produce the phenotypic traits. These genes are capable of mutating and sometimes beneficial traits are inherited. If the inherited trait has survival benefit then this trait will prevail in the population. It is also considered possible that evolution is not a stable or gradual process but that it proceeds in fits and starts. Long periods of stability can be the norm with sudden bursts of evolution occurring in between. This is known as punctuated equilibrium. This is also supportive of Neo-Darwinism.
The evolutionary history of Elephants
Elephants evolved from the tiny, mouse-sized mammals that survived an extinction event 65 million years ago. The first mammal recognizable as a primitive elephant didn't appear until five million years after the dinosaurs disappeared.
That creature was Phosphatherium, a small, squat, pig-sized herbivore that appeared in Africa about 60 million years ago. Classified by paleontologists as the earliest known proboscid (an order of mammals distinguished by their long, flexible noses), Phosphatherium looked and behaved more like a pygmy hippopotamus than an early elephant. The teeth of Phosphatherium are the key as these followed the evolutionary line the led to tusks (elongated incisors).

The two most notable proboscids after Phosphatherium were Phiomia and Moeritherium, which also lived in northern African swamps and woodlands circa 37-30 million years ago. Moeritherium had a flexible snout and primitive tusks. Like a small hippo, Moeritherium spent most of its time half-submerged in swamps; its contemporary Phiomia was more elephant-like, weighing about half a ton.
Moeritherium in profile
Twenty-five million years or so after the dinosaur extinction, the first proboscids appeared that could easily be discerned as prehistoric elephants. The most important of these, from an evolutionary perspective, were the gomphotheres , but the most impressive were the deinotheres, typified by Deinotherium ("terrible mammal"). This 10-ton proboscid sported downward-curving lower tusks and was one of the largest mammals ever to roam the earth; in fact, Deinotherium may have inspired tales of "giants" in historical times, since it survived well into the Ice Age. Deinotherium
As terrifying as Deinotherium was, though, it represented a side branch in elephant evolution. The main branch were the gomphotheres, which used their tusks and trunks to dig for plants in soft, swampy ground. The genus, Gomphotherium, was especially widespread, about 15 million to 5 million years ago. Two other gomphotheres of this era--Amebelodon ("shovel tusk") and Platybelodon ("flat tusk")--had even more distinctive tusks, so much so that these elephants were vulnerable to extinction when the lakebeds and riverbeds where they dredged food dried out. This was a typically Darwinian event.

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Gomphotherium remains and profile

Relating evolutionary theory to Elephant ancestry
The above chart illustrates the development of the modern elephant from the ancestral Moeritherium. The selection pressures faced by ancestors led to morphological changes; tusk shape and size, trunk shape and size and stature, among other traits. Many species co-existed for a while. The modern African and Asian Elephants evolved from earlier ancestors that would have been better suited to the environment of their time. As the environment changed those elephants would have died out. This pattern is best explained by the Neo-Darwinism that embraces “Natural Selection” using the gene as the mechanism for change. The genes responsible for slightly longer trunks prevailed in the population as the longer trunk had more advantages than disadvantages. However, there is also evidence in the chart supportive of the idea of punctuated equilibrium. A burst of speciation occurred in the Miocene and Piocene periods (9 types). Nothing much happened in the Oligocene period and earlier there was a short burst (3 types) in the Eocene period.
Conclusion
Lamarckism cannot be relied upon to explain the evolution of the elephant. It is inconsistent with the scientific facts. There are barriers to accepting Lamarckism as described by Weisemann. Neo-Darwinism operating with the gene as the functional unit is capable of explaining elephant evolution. This is further enhanced by evidence of punctuated equilibrium that is consistent with Neo- Darwinian evolution.