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The Evolving Theory of Evolution

Eosimias, the "Dawn Monkey" was discovered in 1996 in China by Beard and his colleagues, thus filling in a missing link in the evolution of early primates.

It's a Bush, not a Tree

By R. Jay Gangewere 


The museum's new mission statement emphasizes scientific inquiry of the highest standard and sharing that knowledge with the public.

Evolutionary traits are "nested."Just as many smaller Russian dolls nest within one larger doll--they are all similar, except for one different trait…size.

At Carnegie Museum of Natural History educator Diane Gryzbek has to use more than the old Victorian tree to show children how different animal species evolved through time. Today there are better ways for scientists to explain evolution than by that familiar diagram of the big trunk with branches on opposite sides. Now scientists rely on "cladistics"--a way of studying the relationships among organisms such as mammals by their shared "characters"--like opposable thumbs, or ear bones, or hair.Diane, like natural history teachers in museums and classrooms around the world who explain the theory of evolution, needs a new kind of diagram.She needs a cladogram.

A "clade" (derived from the Greek klade for branch) is a group of organisms, such as a species, whose members share similar features derived from a common ancestor. A cladogram shows how species share common characteristics.It’s like comparing the closely related branches of a bush, and identifying similar "characters" on the branches.Christopher Beard, associate curator of vertebrate paleontology, compares it to searching for common traits among cousins, rather than trying to identify the characteristics of more distant relatives, like great-grandparents.Cladistics, or the study of clades, is a research technique that was developed in the 1950s by German entomologist Willie Hennig.Scientists now use cladistics to study all kinds of organisms, past and present.Without cladistics, scientists would never be able to predict that certain animals must have existed, and then search for evidence of them.

In a cladogram several stems grow out of the same linear branch.For example, the presence of a backbone is on the common branch shared by fishes, amphibians, reptiles, and mammals.But further up this evolutionary branch is the stem where animals developed four limbs—which left fish behind.Still further up that four-limbed-animal branch we see another stem--the characteristic of a watertight egg for reproduction.This shared trait narrows the group to only mammals and reptiles.

A big advantage of cladistics is that you can use a computer to search for shared traits. Associate curator of birds Brad Livezey says it's possible to enter hundredsor thousands of "characters" describing a long-dead animal into a database, and then let a computer program run for days or weeks sorting out from millions of choices those evolutionary branches that share these characters."The simplest pattern of unique characters is important," says David Berman, curator of vertebrate paleontology.Because you want to see the most economical ways in which one organism might be related to another.Thirty years ago researchers could spend years sorting out and comparing all the possibilities of how one animal evolved into another animal.Today the computer comes up with important answers by playing a mathematical matching game at lightning speed. 

At Carnegie Museum of Natural History scientists who search for shared characteristics of early mammals have become pre-eminent in their field.In recent years these scientists have earned a remarkable three cover stories in the prestigious journals such as Nature and Science--a feat not accomplished by many institutions, even local universities such as Carnegie Mellon and the University of Pittsburgh.Curator of mammals John Wible argues that Carnegie Museum of Natural History is, at this moment in time, the single most important institution in the United States in terms of research into the early history of mammalian evolution. 

Eosimias, the "Dawn Monkey" was discovered in 1996 in China by Beard and his colleagues, thus filling in a missing link in the evolution of early primates.Previous discoveries showed that there was a long gap in the fossil record of human ancestors, exactly at the stage when the first monkey-like creatures evolved.All the evidence pointed to China as a place where the fossils of these early monkeys might be found. Then he and his colleagues found it, a little animal weighing only fifteen grams (half an ounce) that probably scampered through ancient treetops about 45 million years ago.Finding only fossilized fragments of a jawbone, scientists were able to compare it with the characteristics of other animals and reconstruct the rest of the animal.In the year 2000 it's already a chapter in a textbook used to instruct a new generation of children's teachers.John Wible predicts that the "thumb monkey" from China will become part of common knowledge, like "Lucy" the early hominid from Africa, and "Dippy"--the Diplodocus from Wyoming.
Jeholodens jenkinsi, the earliest complete skeleton of any mammal, was discovered in 1999. Zhexi Luo, associate curator of vertebrate paleontology,published the discovery of this rare mouse-sized, insect-eating mammal that roamed about some 145 million years ago.Its form revealed that early mammals could walk with almost erect gaits. After Luo and his colleagues in China co-published their findings in the British journal Nature, he began working on a textbook presentation. 

Mammalogist John Wible has done similarly outstanding work on early mammal evolution in his studies of marsupials--animals that carry its young in pouches. Likewise Mary Dawson, curator of vertebrate paleontology, is known for her life-long study of the evolution of early rabbits and rodents, through the analysis of their jaws and teeth.

The time between discovery, scientific publication, and popular education has shortened dramatically in the Information Age.At the museum all the scientists point to changes in the theory of evolution in the past decade.We have learned that dinosaurs were probably the ancestors of birds, and that dinosaurs could be good parents, like maiasaurs(the “goodmother dinosaur”).We have learned that tiny early mammals lived in the time of dinosaurs. We have seen the origin of the “cradle of life," which used to be assigned with Biblical overtones to the ancient Middle East, shifted to Africa, with the discovery of "Lucy" and other pre-humans.Now, the discovery of the earliest mammals has spotlighted China.

Research at the frontier of natural history can be hard to translate into popular understanding.In the life sciences such as the study of birds, amphibians and reptiles, botany and mammals, museum scientists have better tools than ever--a molecular lab within the museum itself, the ability to examine DNA sequences, automatic sequencing that is now fast and cheap. 

Livezey often answers the familiar question, "What is it you do?" by saying, "I work with detailed anatomy and modern analytical techniques to explain the history of organisms."Ninety-nine percent of the advanced work in such technical fields is through professional journals an ordinary person could not read.

Behind all the research are the collections--the core information about life forms of the past and the present.Livezey says when kids come into the museum and look up at the teeth of T. rex, and say, "Will it eat me?",he himself is usually looking at its feet and thinking,"These look a lot like the feet of a huge bird."If you want to talk about evolution, hold the foot bones and claws of a bird next to the feet of T. rex and see the similarities.Birds have more in common with dinosaurs than any other life forms, and yet this is an insight that has only gained in popular acceptance in recent years.The physical specimen in a collection is still one of the best teaching tools.

Mary Dawson notes that the sharp-eyed descriptions used by a classic scientist such as Baron Georges Cuvier in diagnosing traits for different groups of animals are still critical. In 1818, the brilliant Cuvier showed how to identify the nature and affinities of an extinct animal from one part or a fragment of a skeleton, and he opened up the theory that the earliest mammals lived in the Age of Reptiles.The weakness of computer analysis is the human definitions of the"characters" of the specimens. A scientist using one set of scientific facts may define an animalvery differently than a scientist using a different set of data.

Scientists have various opinions about collecting. John Rawlins, associate curator of invertebrate zoology (insects), is an advocate for expanding the collections of life forms in museums.Not only does he study the relationships of individual species, he believes we need to preserve now whatever we can of entire ecosystems.He wants to see "The whole Cord automobile working, not just the cylinders." (Cord cars went extinct in the 1930s.)Biodiversity with a big "D" is what Rawlins believes in.On the plant are the parasites the insect eats, then the mammal eats the insects, and then the bird eats the dead mammal--"It's a question of dependency, not which is related to which," Rawlins argues."Preserve the system, and the species will follow." For that reason he believes it is imperative for museums to have as complete a record as possible of the current and past specimens that knowledge is based upon. When the scientific literature is wrong, the scientist must always return to the specimens. 

Practical people are always asking, "What use does this scientific information have?"The answer is surprisingly easy.By studying the original life forms we get answers that lead to applications in the practical world--to modern agro-economic concerns and medical breakthroughs.Chris Beard says that fundamental knowledge of Earth's processes forms the basis of modern civilization.Fossil fuels of oil, gas, and coal power the modern world, and knowledge of the Earth's stratigraphy is necessary for the modern extractive and energy industries. 

The research of Albert Kollar, collection manager of invertebrate paleontology, into the sea life of the ancient past documents many trends we see today: world-wide climate change, the rise and fall of sea level, and increases in the temperature and salinity of the world's oceans. The ancient processes can be seen at work today in the tropical reefs of the Bahamas, with their myriad forms of life specifically adapting and evolving to fit their habitats. Kollar sees to it that the natural history docents have all the updated information they need to use the museum’s exhibits of ancient undersea life to explain such fundamental processes.

As a society we don't do a good enough job teaching and applying the theory of evolution, says Beard.He points out that from the pure perspective of evolutionary time, the bug-eyed primates known as tarsiers were a ten-fold more distinctive than humans.When it comes to preservation policies, the mascots and poster animals of modern conservationists--like pandas and tigers--are less significant than other key groups--such as pangolins, manatees, elephants, tarsiers, and lemurs.While humans have been good at being fruitful and multiplying, we have not done so well at understanding and managing our Garden of Eden.

"Once you start asking the great metaphysical questions," Beard says, "such as 'Who are we?Why are we here?'--and begin to apply reasonand logic to the answer…pretty quickly you'll become a paleontologist."

Seeing Research at the Museum

The new mission statement of Carnegie Museum of Natural History emphasizes "scientific inquiry of the highest standard to create and share knowledge of evolution and environmental change and the interactions with life on earth."Thus there is a new series of“Spotlight on Science” exhibits to stress the work of scientists in the field. Visitors can enjoy popular behind-the-scenes tours, and see into a collection area through a window on the third floor.In Dinosaur Hall a fossil preparator is regularly at work. 

The museum's current research is also summarized on the museum's web site: http://www.clpgh.org/cmnh.Web developer Thomas Feulmer reports that in July, 2000, about 30,000 people per day accessed the site.Thus in one month close to a million people discover what is happening at the museum--including scientific research.



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