Marlene Zuk, author of RIDDLED WITH LIFE, essay in New York Times

The Evolutionary Search for Our Perfect Past
By MARLENE ZUK
New York Times, January 19, 2009

Remember when life was simpler, and diets weren’t full of processed food and chemicals? No, not the 1950s. Increasingly, we are developing nostalgia for a much earlier epoch: the Pleistocene, when humans lived in small hunter-gatherer groups and didn’t worry about high cholesterol.

Although the box-office lure of skimpy fur garments cannot be underestimated, movies like “10,000 B.C.” are popular because they appeal to our sense that life used to be more in sync with the environment. A recent cartoon shows one of those evolutionary progressions — ape to man walking upright to man slouched over a computer — with the caption “Somewhere, something has gone terribly wrong.”

Maybe our woes arise because our Stone Age genes are thrust into Space Age life. That beer gut? It comes from eating too many processed carbohydrates; our bodies evolved to eat only unrefined foods, mainly meat, and we get out of kilter veering from our ancestral diet.

Food allergies and digestive woes? We, like other mammals, aren’t meant to consume dairy products after weaning. When politicians fall from grace after committing adultery, some commentator will always point out that such behavior has evolutionary roots: weren’t the best procreators alpha males with roving eyes?

In short, we have what the anthropologist Leslie Aiello called “paleofantasies.” She was referring to stories about human evolution based on limited fossil evidence, but the term applies just as well to nostalgia for the very old days as a touchstone for the way life is supposed to be and why it sometimes feels so out of balance.

As an evolutionary biologist, I was filled with enthusiasm at first over the idea of a modern mismatch between everyday life and our evolutionary past. But a closer look reveals that not all evolutionary ideas are created equal; even for Darwinians, the devil is in the details. The notion that there was a time of perfect adaptation, from which we’ve now deviated, is a caricature of the way evolution works.

First, when exactly was this age of harmony, and what was it like? Scavenging, or eating the carcasses of dead animals left by (or stolen from) predators like lions, was probably replaced by active hunting and accumulation of wild plants about 55,000 years ago, and agriculture seems to have begun a mere 10,000 years ago. We did a lot of different things during each of these times.

How much of the diet during our idyllic hunter-gatherer past was meat, and what kind of plants and animals were used, varied widely in time and space. Inuits had different diets from Australian aboriginals or Neotropical forest dwellers. And we know little about the details of early family structure and other aspects of behavior. So the argument that we are “meant” to eat a certain proportion of meat, say, is highly questionable. Which of our human ancestors are we using as models?

But the difficulty with using our hunter-gatherer selves as icons of well-being goes much deeper. It is not as if we finally achieved harmony with our environment during the Pleistocene, heaved a sigh of relief and stopped.

Instead, evolution lurches along, with successive generations sometimes unchanged, sometimes better suited to their surroundings in some ways but not others. At any one point, adaptations take place: individuals who can endure heat or cold or famine leave more offspring than their less hardy counterparts. But there is no one point when one can say, “Voilà! Finished.”

Did our cave-dwelling forebears feel nostalgia for the days before they were bipedal? Were hunter-gatherers convinced that swiping a gazelle from a lion was superior to that newfangled business of running it down yourself? And why stop there? Why not long to be aquatic, since life arose in the sea? For that matter, it might be nice to be unicellular: after all, cancer arises because our differentiated tissues run amok. Single cells don’t get cancer.

You might argue that hunter-gatherers were better adapted to their environment simply because they spent many thousands of years at it — much longer than we’ve spent sitting in front of a computer or eating Mars bars. That’s true for some attributes, but not all. Evolution isn’t the creaky old process we used to think it was. Increasingly, scientists are discovering that the rate of evolution can be fast (sometimes blindingly so) or slow, or anything in between.

Marlene Zuk is a biology professor at the University of California, Riverside, and author of “Riddled with Life: Friendly Worms, Ladybug Sex and the Parasites that Make Us Who We Are.”

For the full article, click here.

Marlene Zuk, author of RIDDLED WITH LIFE, essay in New York Times

A Great Pox’s Greatest Feat: Staying Alive
By MARLENE ZUK
New York Times, April 29, 2008

The findings were hardly earth-shaking. They dealt with an obscure bacterial infection found in an equally obscure group of natives in Guyana. Nonetheless, they made headlines.
Why? Because the disease was syphilis. The new research suggested that syphilis originated as a skin ailment in South America, and then spread to Europe, where it became sexually transmitted and was later reintroduced to the New World.

The origin of syphilis has always held an implied accusation: if Europeans brought it to the New World, the disease is one more symbol of Western imperialism run amok, one more grudge to hold against colonialism. Sexually transmitted diseases have always taken on moralistic overtones — they seem like the price of pleasure. We tell ourselves that if we can just make everyone behave responsibly, we can halt the attack.

But we may not have as much say as we might like to think. Infectious diseases are caused by living beings that spread from one host to another, and natural selection will favor anything that increases that spread — say, a higher probability of becoming airborne, or a better means of attaching to the gut wall.

The syphilis bacterium, Treponema pallidum, has no nervous system or brain, no consciousness with which to plot an attack. But it has an ability that is even better: it can reproduce at a rate that leaves us in the evolutionary dust. For any S.T.D., making the host more likely to have sex will benefit the pathogen that causes it. And syphilis may be a case in point.

Detailed records of syphilis infection start appearing in Europe from 1495, and a fearsome disease it was. Smallpox was called smallpox to distinguish it from the great pox, syphilis, which evoked this description from Ulrich von Hutten in 1519: “Boils that stood out like Acorns, from whence issued such filthy stinking Matter, that whosoever came within the Scent, believed himself infected. The Colour of these was of a dark Green and the very Aspect as shocking as the pain itself, which yet was as if the Sick had laid upon a fire.”

Two points are noteworthy about this vivid account. First, it contrasts markedly with modern experiences with the disease. Although serious in its overall effects — which can include heart problems, brain damage and infertility — the rash and other overt symptoms of syphilis are now much more muted, and the disease may go undetected for some time, which helps explain why it is so hard to control. Second, it is reasonable to suppose that a sufferer of the symptoms von Hutten describes would be unlikely to get a lot of dates.

These two observations led Rob Knell, a scientist at Queen Mary University in London, to propose (in a 2004 paper in The Proceedings of the Royal Society of London) that they were connected. If a syphilis-ridden individual were less likely to have sex, and hence spread the disease, it would behoove the disease organism to evolve a less acute effect on its hosts. Syphilis became less severe, he argued, because it was transmitted more readily if victims were still attractive to the opposite sex.

And while these changes were too rapid to be attributed to humans’ evolving resistance to the disease, he continued, for the syphilis bacteria, even a few years represents many thousands of generations. So we have syphilis itself to thank for the lessening of its symptoms. The disease is still serious, of course. But the rapid evolutionary change is striking.

Conventional wisdom used to hold that all diseases eventually evolved toward a more benign state, a “don’t bite the hand that feeds you” rationale. The muting of syphilis notwithstanding, we now realize that is not the case.

Diseases can evolve to become more virulent, more benign or neither — it all depends on what’s in it for them. For some diseases — cholera, for instance — killing the host is immaterial if the pathogen can spread via contaminated water sources. But sexually transmitted diseases must get around via sex. From the pathogen’s perspective, simply sitting around in the intestinal tract waiting for a too cursory bout of hand washing is unsatisfactory.

The disease organism from which syphilis arose is spread through simple skin contact. In chilly Europe, that’s too chancy a mode of transmission. Sex, on the other hand, is a fairly reliable means of transport, even for a delicate bacterium.

So you might blame Columbus, not for wreaking havoc on the New World through the spread of a sexually transmitted infection, but for wearing clothes. If he and his fellow Europeans had been more prone to going about au naturel, maybe the great pox wouldn’t have been so great after all.

Marlene Zuk is a biology professor at the University of California, Riverside, and author of “Riddled with Life: Friendly Worms, Ladybug Sex and the Parasites that Make Us Who We Are.”

For the article, click here.