received the first batch of material, which included three fecal samples from poor Gimble. Hahn’s grad student Mario Santiago did the screening, and again all three of Gimble’s samples tested positive. Santiago then amplified a viral RNA fragment and sequenced it, confirming that Gimble’s virus was indeed SIVcpz. It seemed to be a new strain, distinct enough from other known strains that it might be unique to East Africa. This was significant on several counts. Yes, the chimps of Gombe were infected. No, they couldn’t be source animals for the human pandemic. The variants of SIV found by Martine Peeters in western Africa (this was before Hahn’s own findings from Cameroon) more closely matched HIV-1 group M than the Gombe virus did.
In mid-December, another email from Hahn’s computer went out to Richard Wrangham, Jane Goodall, Martin Muller, and others. Under the subject line GOOD NEWS AT LAST, Hahn described the findings from Gimble and the position of his strain on the SIV family tree. Then, with her characteristic penchant for uppercase exuberance, she wrote: “THIS IS A HOME RUN!”
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That was just the beginning. For nine years the study continued. Fieldworkers at Gombe collected fecal samples from ninety-four different chimpanzees, each of which was known by name and, in most cases, by its individual character and family history. Beatrice Hahn’s people did the analyses, finding that seventeen of those ninety-four chimps were SIV-positive. As time passed, some chimps died. Others disappeared in the forest and were presumed dead when they failed to reappear. Death is often a private matter for wild creatures, including chimpanzees, especially when it comes upon them by slow and painful degrees. They tend to go absent from the social group, if there is a social group, and meet the end alone. Gimble last showed himself to trackers on January 23, 2007. His body was never found.
Back in Birmingham, there was turnover of a different sort, as grad students and postdocs cycled through Hahn’s lab. Mario Santiago departed, heading off for the next stage of his career, and Brandon Keele arrived. Samples continued coming from Gombe, in occasional batches, and those samples were analyzed—a slow and laborious process. Much of the work fell to Keele, though even for him this was “a backburner project.” Keele described to me, during my visit with him at Fort Detrick, the moment of recognition that occurred near the end of his postdoc period, bringing that project to the front burner.
“I was trying to leave and finish up. I said to myself, ‘I wonder what’s happening with these chimps?’ ” He was aware that the number of known SIV-positives at Gombe had increased as the sampling stretched on, and that there was evidence of vertical transmission (mother to infant) as well as sexual transmission accounting for new infections. He thought the study might yield an interesting, undramatic paper about how a harmless virus spreads through a population. “And then we started compiling the data,” he told me. That meant bringing in a dimension of behavioral observations from the field. So he contacted collaborators at the Jane Goodall Institute’s research headquarters in Minnesota and, asking about one individual after another, heard a drumbeat of unsettling news.
“Oh, no, that chimp is dead.”
“No, that chimp is dead. He died in 2006.”
“No, that chimp is dead.”
Keele recalled asking himself: “What the hell is going on?” Part of the answer, revealed when he saw an updated mortality list, was that a wave of untimely deaths had been sweeping through SIV-positive members of the Gombe population.
He and the team at Hahn’s lab had lately written an abstract for a talk he planned to give at a meeting, which would lead in time to a journal publication. The draft abstract, by Keele’s recollection, contained a sentence such as: “It doesn’t really seem that there is a death hazard to infection in these chimps.” They had sent the draft to their partners at Gombe, who responded quickly with news of seven additional chimpanzee deaths, about which Keele hadn’t even known. He scrapped the abstract, thought again about what he was doing, and began working more closely with Gombe and Minnesota to assemble a more complete set of data. Then they would see where it led.
Around the same time, spring of 2008, Keele also heard about some unusual pathology results on tissues from one dead Gombe chimp. The chimp was known as Yolanda, a twenty-four-year-old female. She sickened in November 2007, of an unknown ailment, and came down from the mountains to