(Spoiler Alert: the answer is yes.) According to the Gaia hypothesis, the Earth is a self-regulating complex system. It can be considered a single organism, consisting of many parts, including humans and other life forms, as well as the nonliving environment. When a tissue in an organism, such as a human, behaves in a way that endangers the continued existence of that organism, it can be considered a cancer.
An articulate expression of this possibility can be found in the chilling monologue of Agent Smith in the movie The Matrix:
“I'd like to share a revelation that I've had during my time here. It came to me when I tried to classify your species. I realized that you're not actually mammals. Every mammal on this planet instinctively develops a natural equilibrium with the surrounding environment, but you humans do not. You move to an area, and you multiply, and multiply, until every natural resource is consumed. The only way you can survive is to spread to another area. There is another organism on this planet that follows the same pattern. A virus. Human beings are a disease, a cancer of this planet, you are a plague, and we are the cure.”
In an attempt to illustrate and quantify this concept, I would like to compare all animal life on this planet to a 70 kg man, and the length of time animal life has existed (estimated at 500 million years) to 70 years. The length of time that humans have existed is estimated at 2 million years, or the last 102 days of the man in this analogy. When the genus Homo first appeared on the scene, it was just a barely discernible bump on the skin, just one species among millions.
The total biomass of animal life has fluctuated quite a bit with mass extinctions. The last mass extinction was 66 million years ago, so we can assume that the growth of the animal biomass from 60 years of age to 70 years in this metaphorical man has been fairly steady. Likewise, the growth of human biomass from 2 million years ago (age 69 years, 263 days) to 10,000 years ago (age 69 years, 364.5 days) can be assumed to have been proportional (with the exception of events like the Toba supervolcanic eruption mentioned below).
Before discussing the significance of that 10,000 year figure, let us look at the meaning of cancer and its types. Cancer is characterized by uncontrolled growth. We humans certainly fit this description. Also, put simply, cancers can be categorized as malignant or benign. A feature of malignant tumors is that they not only grow, but also spread, or metastasize. We certainly do that quite well! However even benign tumors can be dangerous when the localized growth crowds out normal tissue. A striking feature of the graph above is that wild mammals have a biomass of only 0.007 gigatons of carbon, compared to 0.1 gigatons for livestock, a 14-fold difference! This is not normal. This is the result of habitat destruction, a crowding out of normal tissue, if you will, by abnormal growth The biological niche normally occupied by wild mammals has been supplanted by livestock, raised (unnecessarily) by humans for their own sustenance. Examples of this include the near extinction of bison in this country and the incredible shrinkage of the range of animals like grizzlies and elk in recent centuries.
My argument here is that the biomass of livestock (first domesticated 10,000 years ago) should be lumped together with humans, in the same way that the vasculature that supports a malignant growth, though not itself malignant, constitutes an integral part of the tumor.
With that in mind, human population 8,000 years ago is estimated at 5 million, 0.2% of our current number, for a combined human and livestock biomass of 0.0003 Gt, or 9.4 grams in the 70 kg man at the age of 69 years and 364.6 days.
Going back further to the Toba supervolcanic eruption 70,000 years ago (age 69 years, 361.5 days), before cattle were domesticated, the human population was estimated to be 10,000, for a human only biomass of 0.00000234 Gt, a mere 73 mg in the 70 kg man, a fairly negligible size, like a large mole.
In 1800 (age 69 years, 264 days, 23.73 hours) humans numbered 1 billion, 13% of the current population for a biomass of 0.009 Gt, 625 grams in the 70 kg man.
With a population in the most recent years of 7.5 billion, the human/livestock biomass is 0.067 Gt, or 4.7 kilograms in the 70 kg man.
So in the last 3.5 days of this man’s life, a little bump on his skin has grown in 3 days to 1/3 the size of his thyroid gland. This might be cause for concern. Nine hours later it weighs the same as one of his lungs. And in the last 15 minutes it has ballooned to 3 times the size of his liver. A reasonable man might want to seek medical attention to have this thing removed.
With five mass extinctions behind us, a sixth one is on its way. This one will be anthropogenic. We will be both its cause and its victim. (Except for a few cell lines like HeLa cells, most cancers bring about their own demise.)
