This post was inspired by Michael Eisen (@mbeisen), who innocently asked about the DNA content of various foods on Twitter a few days ago. As expected, the responses were mostly the rantings of idiots, all sound and fury, signifying nothing. Michael Eisen also brought my attention to a recent Oklahoma State University survey that returned the surprising result that 80% of Americans don’t understand the difference between DNA itself and genetically engineered DNA. Although, there’s some debate about the veracity of the survey, as Ben Lillie (@BenLillie) points out that previous research doesn’t back the claim that Americans are so dense, but I’ve shown before that survey design can alter the outcome.
Due to this cacophony, I remembered an old post I’d abandoned about eggs, or yeitse. (Yeitse is the Russian word for egg. It helps if there is one cool fact that you can take home from any blog post. 🙂 In it, I noted that eggs are virtually DNA-free. So I spruced up the old text and hope that Michael will find it more informative than the usual 140 character Twitter snark.
An egg weighs about 57 grams and contains 213 milligrams of cholesterol. It is about 80% water, and the rest of the weight is evenly split between protein and fat. Eggs have been appreciated as a great source of concentrated nutrients for thousands of years, except for perhaps the last 50. It has been proposed that the building of the pyramids was enabled by the prior domestication of the chicken. Chickens permitted the pharaohs to set up massive, mobile protein manufacturing plants (chicken coops) in any area, immediately adjacent to new construction sites, and thus feed the manual laborers that were their primary source of motive power.
Eggs, as I mentioned, are a rich source of cholesterol. Humans first began to badly misunderstand the egg at the same time that they began to associate, but not fully comprehend, cholesterol and atherosclerosis. When they examined the diseased blood vessels of well fed men suffering from heart attacks, they found disgusting, yellowish gobs of material distorting the walls of these vessels. The material was mostly cholesterol. Not recognizing (or perhaps forgetting) that cholesterol makes up about 35% of every membrane in every cell in the body, and that most of the cholesterol in the human is made especially for this purpose by the liver—they decided that eating cholesterol caused heart disease.
So they took an animal that does not normally eat eggs, and they fed them eggs anyway. They also picked an animal that does not make cholesterol in its liver, like people, but gets it by eating plants. This animal, the white rabbit, developed really bad atherosclerosis when overfed with eggs. So forgetting that people are not rabbits, it was announced that atherosclerosis is caused by the eating of eggs. And most people believed it, and tried to stop eating them.
An egg is just a single cell. You tend to forget that, holding one in your hand and tossing it up into the air. If you were holding an onion of about the same size, you would be holding several million cells. There are other differences between an egg and an onion, but one that really stands out is the amount of DNA. It takes about 30 times more DNA to make an onion than a chicken. That is, the chicken genome contains about 1.8 billion bases, but the onion genome contains more than 70 billion. It’s not entirely clear why an onion takes such a detailed instruction manual, while a chicken can be made using an IKEA version. An egg that you buy in the store usually isn’t fertilized, so it contains only one single copy of the chicken genome. Even if the chicken had sex and the egg was fertilized, there would be only two copies. In an onion, you get millions of copies of the onion genome. None of this would really matter, except that about the same time humans began to misunderstand eggs, they also began to get some funny ideas about DNA.
For as long as humans have been eating, they have been eating DNA. Whether from chickens, or onions, or goose liver—if you eat a cell, you eat DNA. Eating the DNA of another organism isn’t dangerous. Since it occurred commonly prior to January 1, 1958, the government considers it to be GRAS—or Generally Recognized As Safe. GRAS is a technical term used by health regulatory officials. It means, literally, that if a substance has been consumed by people for as long as anyone can remember, then it can’t hurt you. Seems like an odd concept, when you think about alcohol, which has a long history of human consumption and isn’t very good for you… but anyway, DNA falls into this category.
Very soon after people began to be fearful that their heart disease was being caused by eggs, they also began to be fearful of eating DNA, but not all DNA, or at least not most of it. They were specifically worried about recombinant DNA. Now, every time an organism reproduces, the DNA recombines, so all DNA is recombinant, by definition. But still, there was DNA out and about starting in the later part of the twentieth century that had been helped to recombine just the way some human scientists wanted it to. This came to be known as genetically modified, or GM. Again, that’s bad terminology, because DNA is constantly being modified. As stable as it is, DNA is continually damaged, cut, and locally annihilated by reactive chemicals and radiation. So all DNA is GM. Some very special DNA is GM at the behest of humans, and the rest is randomly and senselessly GM at the behest of entropy. So the intelligently modified DNA could be called genetically engineered, or GE.
Someone mentioned to me that it might be particularly risky to eat human genes. Jeffrey Dahmer did it. Not to say that makes what he did OK, but I think something altogether different was responsible for his lack of health and sanity. Likewise, there was the Argentine soccer team who got stranded in the Andes and had to eat each other to stay alive. Then again, there are certain sexual practices that culminate in one or the other of the participants getting a mouth full of semen. I think this was already happening in 1958, so it just might be GRAS. Some people swallow, and some don’t. As far as I know, there is no alleged health difference between these groups. What I do know for sure—one swallow like that contains more human DNA and protein than… well, that’s probably enough said about that.
Admittedly, people who eat human genes sometimes die, but I don’t think it is a causal relationship. It seems to me that eating human DNA can be associated with a risk of infectious disease, and a risk of incarceration, depending on how exactly it is done. In talking with people who fear recombinant DNA, it dawned on me that they were not well informed. They do not realize that when they catch a virus, it inserts copies of its own DNA right into theirs. Often, the genes the virus inserts are clever and malevolent, capable of deprogramming their cells and forcing them to make cloned copies of the virus. That’s quite scary, compared to just making a healthy nutrient as in golden rice or other GM,GE improved foods. It turns out that the genes of biotechnology critics are themselves genetically modified and perverted in ways that ought to induce an acute self-loathing. Perhaps it’s not possible to be virulently opposed to molecular biotechnology and still fully educated about the types of DNA modification and gene swapping routinely indulged in by bacteria and viruses, inside your own body, 24/7.
I notice the government has chimed in, and they are almost certainly wrong, because plant genomes run 3-50 times bigger than most animal genomes. That is because plants bear a heavy load of parasitic retrotransposons—bits of old jumping DNA, like the ones that make corn colorful.
There’s a small 2002 study suggesting that semen enhances mood in women due to all the neuroactive hormones in it.
However, hasn’t been replicated and no one’s going to touch the subject with a ten-foot pole, because… (no idea, really)
Those of us who came of age in the ’60s and ’70s often have the mistaken idea that open and candid conversations about sex are normal both in scientific and social circles. The nutritional, hormonal, and infectious disease associations of such activities should certainly rest squarely within the domain of informed science. Unfortunately, there still exists a stubborn prudishness within society that attempts to ostracize scientists who propose working and studying sexual practice and outcome, and I think it originates from the religious dogmatism that is one aspect of our more recently divisive and polarized politics. No topics in science should be out of the reach of a 10-foot pole, or of a well written grant that could improve public health and understanding. The ubiquity of DNA in the human diet makes it difficult to imagine what extremes in the practice are really worth studying. But I think we should face the topic with an open mind, and invite discussion free from the blushing and snickering that still accompanies most attempts to speak frankly about sex.
Regarding Ben Lillie’s critique of the Food Demand Survey result on labeling foods containing DNA, Jayson Lusk (the survey developer) followed up a month later with another set of one-off questions designed to elicit more information into consumers’ understanding of DNA in food and support for labeling. Lillie’s critique was that the question came amidst others about the government’s role in supporting food safety and next to one about GMOs. This time the questions were purely about knowledge of the basic DNA-related biology of food — e.g., whether all vegetables contain DNA (which a slight majority said “no” to). Once again, over 80% of respondents said food containing DNA should be labeled. Over a third thought the US government already required such labeling.
Most well designed surveys of general public knowledge do tend to return face-palming results just like this one. I was a guest lecturer in a high school biology class 2 years ago and was laughed at because I told the class (and the teacher) that the majority of the fields they had passed on their way to school that morning were planted in GM crops. Which was certainly true – BT corn and Roundup-resistant soybeans predominate here as in most of the US. It’s not clear how our democracy can be based on a well educated and well informed electorate when basic and fundamental facts are widely disbelieved. My particular audience had confused the GM food labeling controversy with the GM food approval process, and were certain that GM organisms were restricted to laboratories.