Special Exhibit in Science Library: Tree of Life

by

 

Our tireless obsession to name and categorize things into categories with impermeable and immutable boundaries is perhaps one of our species’ peculiarities: assigning categories to the numerous and diverse forms of life on Earth can be seen as somehow giving us assurance, in creating an illusion that we may be dominant and in control of species on Earth.

 

A sea urchin may be the last thing to which you would think you are related, but scientists have long known – through studies of the development of embryos – that star fish, sea urchins, sea lilies and sea cucumbers, collectively known as the echinoderms, are the closest relatives of vertebrates,  hence Homo sapiens (exhibit in Science Library, Exley, Spring 2019)

In this exhibit, we strive to make the strange familiar and the familiar strange, by showing modern concepts of relations between groups of animals, which contrast with concepts that became established in the late 1800s, the time of establishment of collections in Wesleyan Natural History Museum, and to which many of us are still, erroneously, accustomed.

For instance, star fish (sea stars) and sea urchins are displayed next to humans and bats, to drive home the point that they are in fact, far more closely related to vertebrates than  to corals or worms. Some living fossils are on show, the most staggering of which is the horseshoe crab, with the modern variety next to a 150 million year old fossil (Jurassic). They really haven’t changed that much in how they look!

 

This horse-shoe crab fossil of Mesolimulus walchii  from the ~150 million year old Jurassic lithographic limestone of Solnhofen, Germany, famous for its amazingly preserved fossils. The modern exoskeletons of the Atlantic Horseshoe Crab (Limulus polyphemus) were  collected along the coast of New England. Despite the large distance in space and time, these ‘living fossils’ have changed their morphology very little.

Modern concepts are to a large extent based on genetic (thus family) relations, as shown in  the  ‘Tree of Life’ that greets the visitor at the front of the exhibit, rather than on external morphology (how things look), as shown in Haeckel’s ‘Tree of Life’ (1879) on the wall behind the exhibit.

The modern ‘Tree of Life’  is based on genomic analyses, and shows that more than two-thirds of the genetic and chemical diversity of Earth’s life forms is within single-celled Bacteria and Archaea, with small cells without a nucleus (prokaryotes). Humans, plants and mushrooms, as well as one-celled organisms with a complex cell with a nucleus (Eukaryotes) share a few inconspicuous branches on the lower right side of the tree: the living world consists mostly of very small but extremely variable and complex organisms.

However, bacteria were not quite appreciated as complex, diverse and ubiquitous at the time when our natural history collections were made, owing  not only to the technological difficulties of collecting bacteria in the 19th century, but also – more importantly – to the fact that they hardly can be exhibited, and lack that inspiration of the awe of nature, relative to  large, much more ostentatious animals. Our exhibit showcases animals, fungi and plants from our collections that by themselves, despite representing an infinitesimally small part of global biological diversity,  document a vast array of body plans, sizes and diversity.

 

The top two shelves of the exhibit show Protostomes, a large group comprising of worms, insects, scorpions, mollusks and their relations. It is somewhat staggering to think that the invertebrates in this group make up the majority of biodiversity among animals, with insect being the most diverse group, and beetles  the most diverse insects. Conspicuous and large furry or feathered animals such as mammals and birds are not that common.

On the wall behind the exhibit hangs a reproduction of a Tree of Life, published by the evolutionist fan of Darwin, and scientific illustrator Ernst Haeckel in 1879, a testimony of the anthropo-centric and human observation-centric mode of science, filled with large beautiful animals that we can easily detect with our unaided senses. It also speaks to a then popular social theory, in which it is believed that complex forms evolved from simpler forms in an uninterrupted linear fashion, the ultimate perfect form of which is represented by European man within the group of Mammals, at the top of the tree.

 

Ernst Haeckel’s ideas on evolution and the position of man on top of the tree was reassuring to a Judeo-Christian view of a world, created by God so that  men could have dominion over it. This version of the tree was the English translation of a figure originally published in German, in a book aimed at the broader public and not fellow-scientists, for whom Heackel presented a more complex Tree, showing the three kingdoms of life (animals, plants and unicellular organisms). It is somewhat ironic – from our modern understanding- that Monera (Bacteria) deserved only the lowest spot in Haekel’s tree.

 

The entire Wesleyan campus is erupting in a celebration of biodiversity, and our changing views of the human position within it. Audible Bacillus at the Ezra and Zilkha Gallery explores interspecies relationships between us and bacteria, while Bestiary in the Davison Art Centre showcases a history of representation of animals in art. Join in the conversation and rediscover your place in the complexity of biodiversity.