Cats, Dogs, Paintings & Flutes: What Does It Mean to Be Human?
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MUSINGS OF A CANCER DOCTOR Cats, Dogs, Paintings & Flutes: What Does It Mean to Be Human? BY GEORGE W. SLEDGE, JR., MD ere’s an old question: what makes us human? By old, I mean Greek philosopher-old. Aristotle pondered this and came up H with a pretty good answer: humans are rational animals, beings capable of carrying out rationally formulated projects. He added that “man is by nature a social animal.” The biologist in me has a quite simple-sounding answer to the question. Homo sapiens, like any species, is defined as (per the great evolutionary scientist Ernst Mayr) “groups of interbreeding natural populations that are reproductively isolated from other such groups.” Currently, there are no “other such groups,” given our ability to elimi- nate close relatives, but once there were. Neanderthals and Denisovans GEORGE W. were natural populations that interbred with our ancestors. SLEDGE, JR., We, their descendants, have lost most Neanderthal and Denisovan MD, is Professor of Medicine and genes, and lost them in a selective fashion. Still, evolutionary biolo- Chief of the Division gists now think about questions such as “were the Neanderthals really of Oncology at iStock a separate species?” The consensus seems to be yes, they were separate, Stanford University. though separate along the lines of horses and zebras. Horses mares mandible whose genomic DNA sorts with modern dogs, the first un- He also is Oncology and zebra stallions, when bred together, make zorses, or zebra mules. equivocal evidence we have of the relationship. Other genomic data Times’ Editorial Board Chair. His OT writing They are infertile. Homo sapiens and Neanderthals were right on the suggests that dog and wolf lineages separated somewhere around experience has edge of infertility. Perhaps as few as 80 parings were responsible for all 36,000 years ago, so “a long time ago” is the current answer. And some been recognized the Neanderthal contribution to the modern human genome. By and quasi-wolves must have worked out with our ancestors even before with an APEX Award large, the answer to “What is a human?” is “Humans are that species that genetic divergence. for Publication that breeds with other humans.” Where that domestication occurred is also something of a mystery: Excellence and a FOLIO: Eddie But that biological answer is both true and remarkably unsatisfying. somewhere on the Eurasian land mass seems to be about as precise Honorable Mention Just having the ability to ask the question may be part of an answer. as is safe to commit to at this point. Regardless, dogs were snapping Award. Comment “Humans are the species that ponders what it is to be human” may be a at our heels before we started farming. Penn State archaeologist Pat on this article and pretty good partial definition. I suspect, though I do not know this for Shipman has theorized that the demise of the Neanderthals might be previous postings on a fact, that cows do not ponder their cowness, nor ants their antness. linked to the partnership of dogs (or wolf/dogs) and modern humans, his OT blog at bit.ly/ OT-Sledge. There has never been a Cowistotle. Cowness and antness, to the extent with the latter two combining to out-compete the former for scarce they exist, are genetically hardwired mindsets. We are hardwired as food resources. Maybe, maybe not, but Neanderthals never seem to well, but we seem to be hardwired for software as much as hardware. have had friends named Fido or Rover. We call the software “culture,” but what stands out is out essential mal- By the way, why did wolf/dogs decide to hang out with our ances- leability, our stubborn refusal to be defined by our past. tors? It is an interesting question. Wolves are loners, and wolves in the I often wish that I was an archeologist. Archeology, it seems to me, wild usually avoid humans right up until they decide to eat us. A recent asks the big question of “how did we get here from there?” In the great paper comparing dog and wolf genomes suggests that the reason is sweep of history, the human experiment seems to be defined by that that most dogs have Williams syndrome. You may never have heard of question of malleability, that transition from hardwired behavior in a this syndrome, since only one in 10,000 people suffer from it (if “suf- constrained physical form to an existence defined by our software. Our fer” can be said to be the right word). Williams syndrome patients are software is now in the process of altering our hardware, but that is a routinely bubbly and extroverted, quite literally the friendliest people relatively late development in the human story. on Earth. They have other health and developmental issues, but the Archeology always gives tentative answers. The average modern is extreme sociability stands out. associated with so much sheer stuff that it is hard to imagine a time The genetic event underlying Williams syndrome has been identi- when material possessions were defined by what one could carry on fied (the loss of a 27-gene stretch of DNA), and its canine homolog one’s back, or in one’s arms, or draped over one’s body. The average turns out to be common in dogs and rare in wolves. The friendliest of modern home, I have read, contains around 300,000 “things.” How wolves also have the Williams syndrome genetic kit, and more stand- many “things” can you carry with you if you are walking across the offish dog breeds are less likely to have the Williams genetic defect. So Bering Strait? Fifty? A hundred? And how many of those make it to maybe dogs were “socialized” as much by a mutational event as by our your grave, and how many graves are ultimately discovered by an ar- tossing chunks of meat to them on the edge of some ancient fire pit. cheologist? The ancient human thingome (an “omics” word I just now Cats represent a later stage in human history, and are intimately invented) barely existed. We are now buried in our thingome. associated with the advent of agriculture. A just-out paper in Nature But there are some answers, and I find them intriguing. Ecology and Evolution dates their association with humans to around First, we seem to have been defined, for much of modern existence, 10,000 years ago in the Near East. The story goes something like this: by our pets. “Pets” isn’t the right word for those animals that shared humans raise wheat, store it, and attract mice. The mice, in turn, at- our space, any more than calling them “domesticated animals” quite tract the African wildcat, Felis silvestris lybica, whose virtues as vermin fits the bill. If cats could speak, they might well claim to have domesti- exterminators are appreciated by our ancestors. As farmers fan out cated us. And dogs are so finely attuned to human behavior that they from the Near East, the now-domesticated cats travel with them. They might be considered relatives rather than pets. eventually travel to the ends of the earth, brought along on ships where How long have humans and dogs hung out together? Dogs are the they guard the stores against rats. oldest domesticated species, so the “man’s best friend” trope is prob- Whether cats are actually domesticated is an interesting philosophi- ably right. The archeologic record is somewhat confusing on this is- cal question, but they tolerate us for the moment because we continue sue. A human grave site dating from ~14,700 years ago contains a dog Continued on page 20 oncology-times.com Oncology Times 19 MUSINGS OF A CANCER DOCTOR ments. This may only represent a flawed archeologic record, or it may BEING HUMAN suggest that art and music represent something crucial about the de- continued from page 19 velopment of the modern human brain, and quite specific to Homo sapiens. I will often see patients who are artists, or patients who are musi- to supply them treats and don’t bother them too much. I find it inter- cians (and with a fairly wide range of instruments, my favorite being esting that while we can easily tell wolf and dog skeletons apart, cat the accordion). I have patients who have dogs and cats, indeed are skeletons are indistinguishable from those of African wildcats. But the passionate about them. These things are so common, so normal for passion felines generate in some humans is undeniable. I had a patient us that we fail to recognize how absolutely extraordinary they make delay potentially life-saving surgery until her cat underwent surgery. us as a species. Medical oncology is the new kid on the block, while My patient could not face the prospect of living without that cat. art, music, and our pets tap into something deeper, something more So, add “humans are the species that lives with cats and dogs” to ancient in the human psyche. Something we are designed for, if it truly Aristotle’s “Man is by nature a social animal.” They may even be the separates us from our closest ancestral cousins. same answer to the “what makes us human” question. We don’t just I once had a patient with small cell lung cancer who presented with socialize with each other, we socialize with dogs and cats. Dogs and brain metastases. The metastases were accompanied by seizures, and cats hung around for purely Darwinian reasons: today there are lots the presenting aura for the seizures was Elvis Presley’s “Blue Suede more dogs than wolves, and far more cats than African wildcats.