09/14/2005
Fishing for Birds
We’ve talked before about animals exhibiting behaviors once been thought to be exclusively human. For example, the famed African grey parrot Alex not only has an extensive vocabulary and the ability to distinguish colors and numbers of objects but also may toy with visitors or new researchers by deliberately giving wrong answers to their questions. We’ve also talked about crows or ravens that have learned to deceive their more aggressive colleagues by pretending to eat at a source that has no food, then switching to the real food location. You may have seen mention of these latter birds in an article in the August 4 New York Times Sunday Magazine section.
In the same vein, Michael Noonan, professor of animal behavior at Canisius College in New York State, has stirred up the animal behavior community with his studies of orcas, killer whales, housed in Marineland in Ontario, Canada. When on Marco Island in Florida, I like to watch the pelicans and gulls follow the fishing boats to the docks, where the birds wait for the fishermen to clean their catch and toss the remains back into the water. Well, one of the whales in Ontario decided to capitalize on the gull’s taste for fish in order to add variety to its own diet.
Noonan noticed that this particular orca would swallow a fish but then spit out the regurgitated fish onto the surface of the water. The orca then sank below the surface, waiting for a gull to take the bait. The orca then proceeded to gulp down the unwary gull. According to an article on the Canisius Web site, Noonan found that, within a couple of months, a younger orca had observed his older brother’s ploy and began engaging in the same gull-baiting behavior. Eventually, all the orcas in that Canadian Marineland were enjoying gulls as a side dish. One or more of the group was a mother orca, a case in which the parent learns from its offspring.
Obviously, this “cultural learning”, in which a behavior is transmitted to and adopted by others in a community, is not only the province of us humans. Although I enjoy finding examples that show we aren’t as different from animals as we may think, it’s clear that we are unique in many respects. What is it that really does separate us from our fellow animals? With the recent sequencing of our human DNA, scientists are trying to find the particular genes or sequences in our DNA that place us in a special category. As an aside, I found an interesting point about DNA in Bill Bryson’s book “A Short History of Nearly Everything”. He points out that no molecule is alive and that DNA is, in the words of geneticist Richard Lewontin, “among the most nonreactive, chemically inert molecules in the living world.” It is this very “unalive”, unreactive nature of DNA that gives us life and allows the DNA to be sustained and transmitted largely unchanged from generation to generation.
Which brings us to poor Clint. Clint died last year of heart failure at the tender age of 24 and I doubt that any of us read or heard of his passing. However, Clint’s legacy is one that may be long remembered in the annals of science. Clint, a resident of the Yerkes National Primate Research Center in Atlanta, was the chimpanzee whose blood was used in an international effort to decode the chimpanzee genome. The work was performed by the Chimpanzee Sequencing and Analysis Consortium, a group of 67 researchers in the U.S., Israel, Italy, Germany and Spain. According to an article by Alvin Powell on the Harvard University Web site, the effort was led by Eric Lander of the Broad Institute (a joint Harvard/MIT collaboration), Richard Wilson of the Washington University School of Medicine in St. Louis and Robert Waterson of the University of Washington, Seattle. It’s clear that teamwork is the name of the game in the DNA sequencing field!
The relatively complete sequencing of Clint’s DNA was announced last month and papers were published in Nature and online by Science. According to Francis Collins, director of the National Human Genome Research Institute, quoted in an AP dispatch by Malcolm Ritter, “It’s a huge deal. We now have the instruction book of our closest relative.” What’s the big deal? With the DNA “instruction books” of the human and the chimpanzee in hand, we’re closer to answering the question, “What makes us human?” Remember that DNA is like a ladder with rungs, the rungs being so-called “base pairs”. The bases are 4 chemicals that we can abbreviate as the letters A, C, T and G; A only pairs with T and C with G. Thus, the “rungs” are A-T and C-G pairs. If we know all the letters on one side of the ladder, we know the letters on the other side.
So, how do we differ from the chimp? All we have to do, it would seem, is lay down the A, G, C, T “letters” in each DNA ladder side by side and see where they differ. It’s not that simple. There are some 3 billion rungs (base pairs) that form the rungs in the DNA “ladders” in each of the chimp and human DNAs. That’s a lot of rungs! What have they found so far? Among those 3 billion base pairs, there are 40 million places that differ in the chimp and human DNAs. Of the 40 million, 35 million are cases where the base pairs differ and 5 million are sites where a portion of the code has been added or deleted. To put the findings in perspective, the differences between chimps and humans are about 10 times greater than the differences between individual humans. There are also 50 genes that we humans have that the chimpanzee does not.
After chimps and humans branched off from a common ancestor some 6 million years ago, both species have evolved, becoming different from that ancestor and from each other. One of the areas the researchers are focusing on is to compare regions in DNA in which genes are changing at different rates in humans and chimps compared to other mammals. The hope is that the sources of various diseases and immune responses in humans and chimps can be traced. We know that chimps and humans have different responses to HIV/AIDS, for example. Indeed, the researchers have found that the most rapidly changing genes in humans, chimps and other mammals are in areas related to immune responses to diseases.
Unfortunately, it isn’t enough to determine which of the “letters” in the chimp and human DNAs differ. The complexity of the problem is noted in an article by Edwin McConkey and Ajit Varki in the September 2 issue of Science. They write, “Can we now provide a DNA-based answer to the fascinating and fundamental question, ‘What makes us human?’ Not at all!” They go on to say that it isn’t enough to see which genes are different. We have to know the function of each gene, what protein or proteins it orders be made (the gene is “expressed”), when and at what stage in the life of the chimp or human this happens and also the effects of environments on the DNA. There’s a lot more work to be done!
The same issue of Science contains an editorial and articles that bemoan the possibility that we have most of the chimpanzee’s DNA figured out but that we are in danger of the chimpanzee itself becoming extinct. Unless poaching, the eating of so-called “bush meat” and loss of habitat due to logging and clearing are addressed, gorillas, chimpanzees and orangutans could be gone within a generation. We owe our closest relatives better than that.
Allen F. Bortrum
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