We marvel over astronomical numbers, but by asking ‘How many cells on Earth?’ we see that biological numbers are vastly larger.
Astronomical numbers are, well, astronomical. By some estimations, there are 2 trillion (2×1012) galaxies, each with about 100 million (108) stars. Factored together, that gives us about 200,000,000,000,000,000,000 or 2×1020 stars.
Each star, however, is also enormous. Our Sun, about average size, has a mass of 2×1030 kilograms. If we multiply that times the number of stars, it gives us 4×1051 kilograms of starmass out there. Even that doesn’t come close to representing the size of astronomical numbers, because there is a much larger amount of unseen ‘dark matter’ and ‘dark energy’ in the universe, which physicists struggle to understand and estimate.
Then there are the distances involved in astronomical numbers. The diameter of the visible universe is estimated to be about 9×1026 meters. It would take a beam of light about 93 billion years to cover that distance.
Advanced Cell Numbers
All of this is impressive, but in our wonder at the universe out there, we sometimes miss the wonder of the universe right here, around us and even within us. For instance, How many cells are there on Earth?
Consider humanity. There are roughly 3×1013 cells in the human body. That is a large number, more than the number of galaxies, but still small by astronomical measures. However, we need to multiply that by 7 billion people alive today, giving about 2×1023 human cells on the planet. That means there are perhaps 100 living human cells for every star in the universe. Biological numbers can also be large.
But we can’t stop there. Even with our current population explosion, humanity makes up a minuscule fraction of living things, and an equally small fraction of the total weight (‘biomass’) of everything that lives on our planet. In a celebrated example, consider that 1/5 of all described species of animals— not just insects, but all animals: mammals, birds, fish, worms and many, many others— are just beetles.1)One evening a group of English clerics encountered the great biologist J.B.S. Haldane. They asked him what his constant study of biology had taught him about the mind of the Creator. Haldane quipped, “An inordinate fondness for beetles.” I could find no estimates for the total number of beetles within all of those species, but it would not be surprising to find that the number of beetles’ cells on the planet greatly surpasses the number of human cells.
The weight of all living things — again, the ‘ biomass’ — of the earth, minus the bacteria, is about 11×1012 kg. Extrapolating from an average 70kg human, this means that humans only comprise about 0.06% of the earth’s biomass. Factoring the number of human cells by our percent of the biomass, gives us biological numbers of about 4×1027 cells on the planet, a million cells for every star.
Bacterial Cell Numbers
But again, that’s without the bacteria and their relatives, and they are critical for answering the question of how many cells on Earth.
By themselves, bacteria on earth represent about 1030 cells, or over 1,000 bacteria for every cell in large organisms like people and trees. Clearly, we could have started our considerations with bacteria to calculate biological numbers, and simply ignored the more complex living things.
On the other hand, the inclusion of bacteria brings up an interesting consideration with plants, animals, and algae, which are classified as ‘eukaryotes’. Within our cells, most eukaryotes carry even smaller entities, ‘organelles’, some of which have their own genetic material (if you remember your high school biology, these organelles are the mitochondria in animals, and chloroplasts in plants and algae). These are believed to be descended from ancient bacteria. They generally number from 100 to 2,000 per cell. For our purposes here, we need to include them in our consideration of biological numbers. If we estimate that there are 1,000 such organelles per cell, that elevates complex organisms to about the number of bacteria, which might double the number we estimated for bacteria alone.
Then there are the viruses. Viruses are not living. If we imagined that our computers were living things, then viruses would be thumb drives. They can’t do any computing by themselves, but they ‘inject’ information that directs the computer. Some thumb drives carry malicious information which takes over the entire machine and forces it to infect other computers with the same contagious software. Which is pretty much what viruses do.
So viruses are not alive, but just as thumb drives are ‘descended’ from fully-functioning computers, so viruses are created from, descended from, and perpetuated by, living things. For our upcoming needs, we should also count them. It is estimated that there may be 1031 viruses on earth, or 10 viruses for every bacterium.
Geologic Time Scale Numbers
We’re still not finished. We must factor these extraordinary numbers over geologic time scales. Life has been on earth for about 3.5 billion years. For simplicity, assume that the average lifespan for a cell is one year.
That is probably generous, since bacteria may not even last that long. On the other hand, ‘lifespan’ is hard to define in microbes, some may survive indefinitely. Consider the beer, Flag Porter 1825.2)Produced by the Darwin Brewery, ironic for our discussion here. It is brewed from yeast which was recovered in 1988 from a ship that sunk in the English Channel in 1825. Obviously, some of the yeast in it survived 150 years.
Far beyond that time span, however, we could also make the argument that bacteria can live 3.5 billion years. Because bacteria only divide in direct lineages without sexual reproduction, we could argue that the very first bacterium is not only still alive, it now numbers 1030 in population. In fact, we could argue that all living cells, organelles, and viruses, are still the first bacterium. That one-celled jot has simply divided repeatedly throughout the diversification of life on the planet. We could take the view that the original bacterium lives on somewhere within every existing cell and virus.
Returning to our calculations of biological numbers, if we take the number of living cells and viruses and multiply them times 3.5 billion years, that gives us gives us about 1040 cell and cell descendants through biological history. That is the largest answer to the question of ‘How many cells on Earth?’
But compare those 1040 cell and cell descendants to 2×1021 stars; Easily, since the beginning of life on earth there have been over a quintillion cell descendants for every star in the universe.
Of course as we noted, each star is staggeringly massive when compared to a bacterium. But that is inevitable. All of these biological numbers have appeared on a negligible mote of dust orbiting an average star, tucked away into the margins of an unremarkable galaxy. Given that insight, which is the more impressive, the astronomical numbers of a massive star with its powerful, matter-shearing forces? Or the biological numbers presented by the minuscule bacterium with its fabulously intricate molecular gearbox?
Each cell demonstrates a peculiar, finely-tuned and precisely repeatable organization and complexity which stars do not have.3)‘Repeatable order’ and ‘complexity’ are not so clear, nor easy to defend as one might think. Every star is perfectly ordered. It’s just that we cannot track, measure, nor fully understand the order. Within a star, we only calculate extremely small atomic interactions, and extremely large mass effects. The repeated order of the cell, however, is well within our ability to track and understand, at least roughly, from atom to complete cell. The precise, mechanistic repeatability of cells is not found in stars. Beyond that, each cell line copies and recopies its own highly controlled, and minutely faithful, order into yet other cells. This does not happen in stars.
But the most important idea in all of this, and one for which we will need these numbers in future discussions, is that we do not believe that the basic patterns of the universe have changed over the past 3.5 billion years. During the time that life has existed on this planet, we do not believe that any fundamentally new processes, nor entities, have appeared in all of those vast entities out there in the universe.
Correction: we don’t believe that those basic patterns have changed anywhere outside of Earth. Because over that same 3.5 billion years, life has changed rapidly. It has evolved, innovated, and progressed: throughout that enormous time scale, new kinds of cells and new kinds of life have appeared, and continue to appear. In addition, those new kinds of life have constantly fabricated entirely new, highly complex products. This is the fundamental difference between biology and physics: biology innovates.
Life evolves, which means it gives us completely new things to study, things which did not exist before. Without life and natural selection, there might be no novelty in the universe. It’s an important insight, because I will argue that all novelty—biological, artificial, digital—follows some basic biological principles.
Prospective Science and Progress
This difference between biology and physics brings up another consideration, and one which offers problems for scientific investigation: the hard sciences are necessarily retrospective. They look at what already exists, and extrapolate from there.
Which means they are not always prepared to consider the future. Biology, particularly the ‘soft science’ side of biology, considers such things frequently. Evolutionary biology is both retrospective and prospective, biologists look backward and forward. Biology constantly tries to understand things that did not exist before, and which have no precedent. Again, I will propose that the tools of biology can help us to understand innovation, creativity, and human progress. That is where we are headed.
So the point of all this is not scientific one-upmanship, the goal is not for biology to claim some superiority over astronomy and chemistry. All disciplines contain an infinite number of problems to solve, which will require the focus of the greatest minds we have. We will never know everything about any topic in nature. In all disciplines, we are dealing with numbers, and problems, that are just too large to understand.
And, as I will suggest in upcoming essays, it is exactly those incomprehensible numbers that are critical to understanding innovation.
I am pre-publishing this sequence of essays here and in social media to elicit comments and other feedback. They will form the framework for my next book, Darwin, Dada, Dalí, Duke, & Devadevàya.
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Pictures of the Tarantuala Nebula and the Ebola virus courtesy of Wikimedia.
Footnotes [ + ]
|1.||↑||One evening a group of English clerics encountered the great biologist J.B.S. Haldane. They asked him what his constant study of biology had taught him about the mind of the Creator. Haldane quipped, “An inordinate fondness for beetles.”|
|2.||↑||Produced by the Darwin Brewery, ironic for our discussion here.|
|3.||↑||‘Repeatable order’ and ‘complexity’ are not so clear, nor easy to defend as one might think. Every star is perfectly ordered. It’s just that we cannot track, measure, nor fully understand the order. Within a star, we only calculate extremely small atomic interactions, and extremely large mass effects. The repeated order of the cell, however, is well within our ability to track and understand, at least roughly, from atom to complete cell.|