Evolution is not simply change. Stars change, planets change, galaxies, mountains, rocks, and all aspects of the physical world change, but they do not evolve. Evolution implies more than simple change: it is an accumulating, progressive change that relies on the transmission of information from one state of matter to all future states. In life, this transmission of information is chemically mediated through the informational molecule of inheritance, DNA. Natural selection is the process that selects which states are most likely to pass their information, but without inheritance (a term that means the passing of information from one generation to the next) there is no evolution.

For example, if a cell were to develop a much better way to produce energy, it would prosper and probably fare better than any of its neighbors.  But if the new information about how to produce energy is not faithfully copied and transmitted to the next generation, there will be no accumulation of that new information and no evolution.

In living systems, this process of information transfer is highly robust and  leads to a steady, semi-irreversible accumulation of informational change. Robustness means that once a novel improved phenotype is produced, it doesn’t go away unless it is replaced by an even more improved phenotype. Without this stability, evolution would not work. This explains why some features of modern cells have not changed in billions of years: other features of modern life forms are continuously changing (body shape, organ physiology), but the more basic features are fixed.

We know of another form of evolution in the universe that behaves in a very similar way in that it involves passing down information to subsequent generations, but the mechanism of transmission is entirely different from what happens in biological evolution. I’m talking about human cultural evolution. Here the information that is passed from one generation to the next and that spreads throughout the population based on a form of selection is knowledge, carried by language.

In cultural evolution, the information transfer process has led to dramatic leaps of greater efficiency and accuracy of information processing leading to more rapid cultural evolution in a similar kind of positive feedback loop that we find in biological organisms. The steps involved for human cultural evolution are talking, memorization of verbal information, writing, printing, and more recently electronic information storage and transmission, most notably through the internet.

A clue to the similarity between biological and cultural evolution is the similarity in the shape of the curve of the relationship between time and change, or the rate of change function. In both cases, the rate of change began at a very low level, and then as improvements accumulated, including improvements in the evolutionary process, the rate began to accelerate exponentially. This is clear from any measurement of change rates in either model.

This coincidence points to a fundamental law of evolution that should apply to both biological and cultural evolution, defined as a progressive, accumulative (meaning mostly irreversible) process based on information transfer.

Evolution can be robust, progressive, and to a large extent irreversible, and still allow for – in fact require – extinctions. This includes things that might appear to violate the irreversibility rule, like loss of genes, or – on a phenotypic level – loss of limbs, sight, or any feature that improves the fitness of creatures living in a particular environment. So is the acquisition of limbs by land animals really irreversible if whales have lost those limbs? Yes, it is, because whales have not actually gone backwards – they have moved forward in a different direction based on a change in environment. Their limbs didn’t “devolve” back into fish fins, but  continued to evolve in a new direction. Even genetic losses are not really a reversible process, chemically speaking. Gene deletion is not the same as the reverse of gene formation – it is a forward moving evolutionary process that continues to be driven by natural selection.

What about the losses in cultural evolution? Think of all the dead languages, vanished cultures, forgotten technologies. Again, yes, extinctions are common, but the extinction of culture is not the reverse of its development – it is a change brought about by environmental conditions.

The progressive nature of biological evolution and cultural evolution does not mean that we can predict their direction, or that the direction of either is necessarily toward “good”, “better”, or even more complex But since selection is the rule in both cases, we can conclude that there are directions for biological evolution and cultural evolution and that innovation and increased adaptation to the environment will prevail. Overall, and with many exceptions, this also leads to an increase in the maximum degree of complexity at any one time. This doesn’t mean all organisms get more complex, or that all humans use more complex technology over time, but that the degree of complexity among some group of creatures does increase with time, and the complexity of the technology of some group of humans does likewise.