Pascal Gagneux, one of the few laboratory scientists who has studied wild chimpanzees, is a walking encyclopedia of chimpanzee/human differences. Ever since scientists began studying chimpanzees, they have emphasized our similarities, which are striking. But today, neither Darwinists nor conservationists need such similarities to further their respective causes: abundant genomic evidence supports Darwinian evolution, and laws and regulations are in place to protect all endangered species, regardless of whether they are cute enough to excite human sympathy. This has paved the way for chimp researchers like Gagneux to focus on what separates us from chimps. Their goal is to sharpen our understanding of what makes a human human.
In Gagneux’s case, he and his colleagues are hoping to use their analysis of the differences between human and chimp sperm—especially the sugars that adorn the sperms’ surfaces and let them bind to cells in the walls of the uterus or a fallopian tube—to unlock one of the riddles of human infertility: does sperm sometimes have components that undermine its ability to fertilize an egg? Perhaps the differences between chimp and human sperm can help explain why humans miscarry nearly 50 percent of all conceptions, while chimps seem rarely to lose an embryo or fetus.
To get at such questions, Gagneux has spent many hours fashioning devices to coax sperm from chimpanzees. He began by sculpting a silicone version of a female chimp’s rear end. But the male chimpanzees at the Primate Foundation of Arizona that were recruited to help with the project did not see it that way, and the model sat unmolested on a counter. “It’s a nice chimp butt, but I thought it was a bonobo butt when I first saw it,” Jim Murphy, the foundation’s colony manager at the time, admitted to me when I visited a few years ago. “Maybe that’s why they don’t like it.”
Gagneux’s next attempt relied more on medical science than on art. He modified a piece of PVC pipe to create a variation on what’s known as a Penrose drain, which is used to remove pus and other liquid discharge from wounds. For the chimps, the pipe was rigged with a compartment that holds warm water; latex coated with K-Y Jelly lined the interior.
On this day, Rachel Borman, who had worked at the foundation for 10 years as an animal handler, was given the job of selecting a sperm donor and encouraging him to produce a sample. Borman ﬁrst “gowned up” to protect her clothes. The target donor today was a 16-year-old named Shahee. Borman asked me not to follow her into the space that held the caged chimps, as the presence of a stranger might break the mood. So I peered through the glass portal in a door. “I’m just going to go in there with these other guys to make him jealous,” Borman told me as she entered the chimp space. She did a quick pass by Shahee’s rivals and returned to the supply room for the modified Penrose drain. With it in one hand and a training clicker in the other, Borman walked toward Shahee. (Trainers use clickers in tandem with positive reinforcement, usually food, to condition animals to perform a specific behavior—in this case, masturbation.) After a few clicks, Shahee stuck his erect penis through the bars. Borman held up the PVC pipe and said, “Good boy! Good boy!” She then gave him an M&M, and walked back to the lab. “He did it,” Borman said proudly.
Borman cracked open the tube. Lying on the tan latex was a chunk of chimp sperm about the size of a small wine cork. I say “chunk” because most of it had coagulated into what is known as a plug, about one-quarter of which usually melts in the warm vaginal vault. Using a Popsicle stick, Borman transferred the ejaculate into three vials. “It’s fun for the chimps to do this,” Borman explained as she capped the vials. “They love it.”
My job was to shuttle the vials to San Diego when I flew home that night, and then drive them to Gagneux’s lab at the University of California at San Diego so he could study them while the sperm were still alive. As we exited the enclosure, we passed Shahee. He spat on me.