by Nick Lane
Subtitled “The Ten Great Inventions of Evolution”, this book devotes a chapter to each of most prominent steps in the evolution of life. Those ten steps are:
1. The origin of life.
Obviously, the most important step in the evolution of life is its nativity. A vast amount of research has been carried out to figure out how it could have happened, and Mr. Lane presents what I gather to be the latest thinking on the problem: that life originated around deep sea thermal vents. At first, this notion surprised me, but after some reflection I realized that this is a much better solution than the idea of life originating in photosynthetic reactions. The chemistry at a deep-sea vent is much more straightforward than the chemistry of photosynthesis. Thus, the earliest forms of life were driven by the chemical reactions when the hot, mineral-saturated waters emerging from the thermal vents encountered the cooler surrounding waters. The temperature difference alone is a powerful source of negentropy, and the high temperatures drive faster chemical reaction rates. Throw in all those reactive chemicals emerging from the vents and you have plenty of negentropy to build up a self-sustaining system – life.
Central to any biosphere is the ability to continue itself, one means of which is reproduction of the fundamental units of life (cells). Such reproduction must, however, provide a clear blueprint for reproduction, and DNA was the means produced on earth. Scientists now believe that DNA was preceded by RNA in the evolution of life. At first, RNA served as a highly specific catalyst for important metabolic reactions. DNA came along later as a kind of “permanent storage” RNA, a superset of RNA that not only stored the plans for individual RNA molecules, but permitted reliable reproduction. The complexity of RNA and DNA obviously required a long time, but remember, life had billions of years to work this out, and we now estimate that DNA was in use about three billion years ago.
This provided the mechanism for life to break out of its thermal vent prison. This step is still difficult to understand, because we’re talking about cells moving from deep-sea vents to the surface, and somehow developing photosynthetic chemistry while isolated from their earlier source of sustenance. Perhaps photosynthesis arose at vents close to the surface -- but conventional thermal vents are always deep down on the ocean floor. Perhaps there was a transitional phase involving hot springs on the surface, populated by the non-photosynthetic cells, some of which developed photosynthetic capabilities while still sustained by chemical negentropy. Certainly the scale of time and surface area of the earth supports the chances of such an event.
These are the complex cells, far larger than the bacteria which until two billion years ago constituted all forms of life. Their development seems fairly easy to explain: some bacteria that eat other bacteria for sustenance absorbed cells that, for some reason, they failed to digest into components. Instead, the newly-absorbed bacteria were assimilated Borg-like into the now-larger carnivorous cell. This process apparently went pretty far, because many eukaryotic cells contain dozens or even hundreds of internal subcells. Many of these are mitochondria, factory cells that convert simple compounds into ATP, the primary energy source for most reactions inside the cell. These mitochondria have their own internal DNA – a detail that permits us to track mitochondrial DNA and draw deductions about the distant past of many species.
The development of sexual reproduction (as opposed to simple mitosis, in which a cell divides into two copies of itself) was a huge step forward. Some controversy attends our thinking on the origins of sex, but its advantages are undeniable. By mixing genes from two different individuals, the resulting organisms can more readily play mix-and-match games with DNA that permit more rapid response to environmental changes. Simple mitosis permits only slow evolution arising from damaged DNA. Such damage occurs rarely and usually results in defective cells which quickly die. But by combining genes from two healthy cells, we get much more variation to work with, and the variation is less likely to be fatal (because we’re mixing healthy genes). An important condition for success is the creation of multiple progeny. If two cells use sexual reproduction to create two new cells, the odds are highest that the daughter cells will be no better than the parents; next highest are the odds that the daughter cells will be worse than the parents; and the lowest odds are that the daughter cells will be in some manner superior (better adapted to the environment) than the parent cells. Obviously, if two parent cells create only two daughter cells, then the probabilities point towards steady degradation of the line. Only by creating many daughters do the two parent cells have any chance of generating an improvement.
Here I think that Mr. Lane made a mistake: he should have put in multicellular creatures here. Multicellularity required more than the simple agglomeration of cells: in order to make it happen, a single cell – the egg – had to possess the ability to carry out multiple mitosis events in which daughter cells differentiated into specific organs because of the chemical environment they were in – which in turn required that some of the daughter cells act as “pathfinder cells” by emitting the chemicals that guide others to differentiate correctly. This took a lot of steps and was, I think, a huge leap forward. Moreover, it was a precondition for Mr. Lane’s sixth step. Although individual cells do move, Mr. Lane’s chapter is devoted primarily to the wondrous biochemistry of muscle cells. It is indeed amazing how the proteins inside these cells can contract upon command. But such cells would never have developed until after multicellularity developed.
We have a pretty good idea of when this happened: about 650 million years ago. Even more surprising, the entire process took only 5 to 10 million years to produce modern eyes. That in turn kicked off the Cambrian Explosion, in which a huge cavalcade of major new forms of animal developed. Vision allowed herbivores to find their food more easily; it permitted carnivores to hunt down their prey; and it permitted prey to see and flee from carnivores. This hunter-prey relationship kicked off a huge range of biological experimentation. Some herbivores got bigger so that they could better defend themselves; some predators got bigger to take on the bigger herbivores. Some herbivores developed armor plating; carnivores responded with bigger teeth. Some herbivores developed faster speeds to escape with: carnivores responded with greater speed of their own. Some species developed camouflage techniques to hide from predators. And so on and on through hundreds of completely new animal designs. In subsequent eons, many of these exotic life forms went extinct, leaving only a few surviving basic styles, one of which – the chordates – now contains all the vertebrate animals plus a few weird invertebrates.
8. Hot blood
This is really just the idea of temperature regulation. Lots of animals are cold-blooded – they make no effort to control their temperatures, which rise and fall with the environment. Maintaining body temperature is hugely expensive: a warm-blooded animal needs between 10 and 100 times as much food as a comparable cold-blooded animal. The advantages of temperature regulation are, obviously, very great to justify such a huge increase in food intake. For example, a cold-blooded animal must find a good hiding place when temperatures fall too low, because lower temperatures mean lower metabolic rates and a much reduced responsiveness to threats. In other words, a cold lizard can’t run away when a predator approaches. Here’s another advantage: warm-blooded creatures can forage at night, when it’s too cold for the cold-blooded animals to function. Thus, warm-blooded animals can literally “eat the lunch” of cold-blooded animals.
Here, again, Mr. Lane errs. What is it about human vanity that insists upon robing itself in some magic element? For millennia it was the soul; nowadays we modern sophisticates instead pride ourselves in our consciousness. But the thinking is the same: somehow we are invested with a powerful, magical element that defies the laws of physics. Serious physicists have suggested that there is some special, as yet undiscovered force of nature that animates our consciousness. Mr. Lane caters to such thinking, believing that there is something so unique about human consciousness that it must be placed above the known laws of physics. What horseshit! I have already written on the topic of consciousness, explaining just how it developed and how it works. Basically, it’s just a form of mental recursion in which we apply our known rules of social interaction to ourselves. Perhaps I should expand on that essay; it’s quite old.
It would seem that death is some sort of evolutionary anomaly: after all, the best way to keep your genes in the gene pool is to stay in the gene pool forever! Beginners often suggest that death is an evolutionary advantageous development because it removes the old, outdated genes from the gene pool. This runs afoul of the fundamental truth that genes don’t work for the benefit of the species – they work for the benefit of the individual they belong to. Genes that benefit the species as a whole at the expense of their owner die out with their owner. Indeed, it appears that all cells have “autodestruct” mechanisms that, under the right circumstances, kill the cell. Why in the world would any such feature appear in the genes of any cell? There are two reasons: first, if the cell has been invaded by a virus or bacterium, and it senses the invasion, it self-destructs just as any self-respecting starship captain would self-destruct his ship if it were taken over by bad guys. Second, if the cell is going cancerous, then it should self-destruct to protect the rest of the body.
At this point, you might raise the same objection that I mentioned earlier regarding the death of the individual “for the good of the species”. If an individual shouldn’t commit suicide for the good of the species, why shouldn’t a cell inside the body behave in the same way? The answer is that the relationship of cell to body is not at all that of individual to species. The other cells in the body all share exactly the same DNA that the potential suicidal cell has. If the stricken cell self-destructs, that increases the chances that its genes will prosper in the gene pool. If it refuses to self-destruct, that decreases the chances that its genes will gain in the gene pool. So the analogy to the individual versus the species doesn’t apply here.
Here is where I part company with Mr. Lane, who thinks that death can be overcome by medical technology some day. He sees no reason why we can’t forestall the aging of cells. I see a completely different process at work. To explain, consider the role played by the immune system. Its job is to locate, attack, and destroy any foreign cells in the body. This is tricky business, though, because many diseases have learned how to disguise themselves. Thus, the immune system must make a very fine judgement call when it encounters a slightly unfamiliar cell: it must either attack and destroy it, or leave it alone. If the immune system is insufficiently aggressive in this process, then foreign cells will multiply inside the body and kill the host. But the solution is not to make the immune system infinitely aggressive, because it can’t be certain of misidentifying a cell. If the immune system is too aggressive, it will end up attacking native cells. Such mishaps are called auto-immune diseases. If you think about it, the ideal immune system will find the perfect level of aggressiveness when the number of hosts who die of foreign disease is equal to the number of hosts who die of auto-immune disease. That’s the balance point that every immune system searches for, and I think that the immune system of Homo Sapiens is pretty close to that ideal.
Now let’s apply the same thinking to cell death. A cell has its own kind of immune system, its autodestruct mechanism. If that autodestruct mechanism is too aggressive, then too many cells will die and the host will age rapidly and die early. If, on the other hand, the autodestruct mechanism is insufficiently aggressive, then over the long run, cancerous cells will proliferate and kill the host. Thus, the autodestruct mechanism is fine-tuned to reach the ideal level of aggressiveness. Note, however, that this level of aggressiveness is always greater than zero: cells will autodestruct, and the mechanism that triggers the autodestruct cannot be perfectly correct in its recognition of dire circumstances. It will err, which means that healthy cells will occasionally autodestruct. As more and more healthy cells autodestruct, the individual ages and eventually dies. In other words, death is the inevitable result of cancer. You may not die from cancer, but old people die because of it.