Yale Bulletin and Calendar

February 15, 2008|Volume 36, Number 18

A life-sized model of a Rafflesia plant — a leafless, stemless, rootless plant that does not use photosynthesis but bears one of the world's largest flowers — is featured in the "Tree of Life" exhibition at Yale's Peabody Museum.

Exhibit traces linkages on the ‘Tree of Life’

It may come as a surprise to learn that the fearsome Tyrannosaurus rex is closely related to the tiny hummingbird, or that, lineage-wise, mushrooms are closer to humans than they are to a lily.

These are among the facts visitors learn at the Yale Peabody Museum of Natural History’s new exhibit “Travels in the Great Tree of Life.”

A “family” tree showing how all living things — from the smallest microorganism to the largest vertebrate and redwood tree — are related is the highlight of the exhibition, which opens on Saturday, Feb. 16, and will be on view permanently.

Curated by Peabody Museum director and noted Yale botanist Michael J. Donoghue, “Travels in the Great Tree of Life” explores the complex relationships that link organisms. The idea of the “tree of life” — and the term itself — originated with Charles Darwin, whose first sketch of a tree depicting phylogenetic relationships was an 1837 notebook entry. In his 1859 master work “On the Origin of the Species,” Darwin crystallized the idea that species share common ancestors and referred to the genealogical relationships among all living things as “the great Tree of Life.”

The Peabody exhibit reveals the history of similarities and differences among the lineages of organisms as they have changed through time. This chronicle of past evolutionary events is central to understanding the process of evolution and, thus, the interpretation of all biological information, says Donaghue, noting that this history of evolutionary events is the framework for our modern understanding of biology.

Using specially commissioned films, multimedia interactives and specimens (both live and from the museum’s collections), the exhibition demonstrates the full diversity of life and how one form of a species evolves into another through evolutionary time. The exhibit also underscores an important evolutionary concept: that the “phylogenetic relationship” refers not to similarities and differences among organisms but to the relative times that they shared common ancestors in the past.

Some animations in the exhibit take viewers back in time to see, for example, what the ancestral species of a scorpion may have looked like at different points of its evolution.

A computer game invites visitors to respond to a cat’s appeal to “Help me find my home in the Tree of Life.” Using a touch screen, museum visitors respond to five questions about phylogenetic relationships. Each correct answer moves the cat from the beginning of life at the base of the tree all the way to the cat’s branch in the Tree of Life. Interesting “phylo-facts” are learned along the way.

Also featured in the exhibit is a pair of live Black and Rufous Giant Elephant Shrew brothers that were born on Feb. 4, 2007, at the Smithsonian’s National Zoo in Washington, D.C. These tiny animals, the exhibit reveals, are related to the world’s largest mammal, the elephant. Both are members of the mammal lineage Afrotheria that includes some 80 species that are so varied that in-depth DNA analysis is required to prove they share a unique common ancestor. This group also includes the aardvark and manatee.

Exhibition visitors will discover how organisms that look very different can be quite closely related and that similar-looking organisms might be only distantly related. For instance, the body of the whale is similar to that of a fish, but its ancestors were terrestrial and walked on four limbs. As they adapted to swimming, their limbs were reduced and their body shape converged on the typical fish shape.

According to scientists, there are some 1,750,000 known living species, with new ones being discovered every day. The real number may be over 10 million. Some 100,000 species have been included in formal phylogenetic analyses so far — about 5% to 10% of the known living species and only a fraction of a percent of those that have ever existed.

One recent phylogenetic discovery concerns Rafflesia, a group of 13 rare plant species whose closest relatives have remained a mystery for nearly 200 years. Leafless, stemless, rootless and non-photosynthetic, they lack almost all recognizable structural plant features other than boasting the world’s largest flowers. Their flowers lure pollinating flies to their blossoms by mimicking decaying animals on the forest floor.

A breakthrough in the mystery surrounding Rafflesia came in 2007 with the finding that they belong to the plant group Euphorbiaceae, the euphorbs. Related euphorbs have tiny flowers, implying an astounding rate of increase in flower size along the line to Rafflesia. A life-size model is featured in the exhibition.

In addition to the elephant shrews, the other living organisms featured in the exhibit are carnivorous plants, succulent plants and anthropods. Representing the latter are the scorpion and whip scorpion.

In addition to informing the world of the diversity of life on Earth, phylogenetic research is also important in areas as diverse as human health, natural resource management and agriculture, according to exhibition organizers. “Travels in the Great Tree of Life” examines how knowledge of the Tree of Life is being used to save endangered species and understand the origins of disease.

The Peabody Museum of Natural History, 170 Whitney Ave., is open 9 a.m.-5 p.m. Monday-Saturday, and noon-5 p.m. on Sunday. Exhibits and most programs are free with the price of admission. Admission is $7; $6 for seniors; $5 for children ages 3-8; and free for museum members and children under age 3. Admission is free for all on Thursdays, 2-5 p.m. For more information, visit www.peabody.yale.edu or call the Infotape at (203) 432-5050.

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