By Andy Ford
The book Major Transitions in Evolution, by British biologist John Maynard Smith and Hungarian biochemist Eors Szathmary, gives another brilliant confirmation of the theories outlined by Karl Marx’s closest collaborator, Frederick Engels, in his Dialectics of Nature, first published in 1883.
In interviews, John Maynard Smith even referred to his ideas as a theory of “revolutionary development” in evolution, as opposed to a gradual evolution purely by the accumulation of small changes. The authors see the evolution of life proceeding by periods of gradual change, adaptation and variation, punctuated by huge transformations that give rise to new and more complex forms.
Smith and Szathmary identify nine major steps, or in Engels’ language, qualitative changes, that have taken place in the evolution of life. None of these changes can be explained by the gradual evolution from one state to another – a new level of biological organisation had to come through a dramatic re-organisation of living material and of the information required to transmit and reproduce life.
In order, these nine transitions are: (1) the origin of life itself, as self-replicating chemicals; (2) the grouping of single, replicating molecules or genes into chromosomes which contain many self-replicators; (3) the transition from life coded by RNA to DNA, as purely an information-storing molecule; (4) the origin of bacteria as cells containing chromosomes; (5) the transition from bacteria to single-celled organisms; (6) the transition from single-celled organisms to multi-cellular animals, plans and fungi. Once these groups had evolved, many species, but not all, transitioned from reproduction by asexual budding or cloning to (7) reproduction by sex. They also see two further transitions within the animal kingdom: (8) the rise of social insects; and (9) the development of human society. None of these transitions, they argue, can be explained by a simple evolution from what went before.
Self-replicating molecules evolved in some way
The first transition, from chemicals to self replicators, is one of the knottiest problems in biology. The simple organic compounds which are the building blocks of life – amino acids, aldehydes and fatty acids, and sugars – were shown in the 1950s to be quite a likely outcome of the interaction of lightning and methane, with ammonia and nitrogen in the atmosphere of the early earth. Some of these compounds have also been found in comets, asteroids and around other planets. However, it is still unclear how or where the resulting organic chemicals first became able to reproduce themselves – most scientists favour deep sea vents, but alternatives include volcanic mud pools or metallic surfaces. This mystery remains unsolved.
Nevertheless, we are here, so it must have been solved. The next step was for the self-replicating chemicals to be able to organise themselves into templates ready for use in protein replication, what we see today as chromosomes. This step is constrained by what is termed ‘Eigen’s Paradox’ – that for effective replication enzymes are required and yet the genetic code required to make enzymes is too long to be made without enzymes. Another mystery for science to solve.
The third transition is from an ‘RNA world’ where RNA carries out both the functions of enzyme activity and that of storing genetic information, to a ‘DNA world’ where DNA stores the genetic code while the role of RNA is reduced to the translation of the genetic code to create sequences of amino acids to form proteins. RNA can work as both code and enzyme, although it does each inadequately, whereas DNA is a much better information store, being more resistant to mutation and damage. We can see the traces of this early division of labour when we examine a modern cell – DNA genes bind to RNA molecules in the cell nucleus and the RNA then moves off into the cytoplasm where it binds to amino acids in the order originally coded by the DNA. The resulting sequences of amino acids form proteins which fold into particular shapes to form enzymes and structural proteins. It is these enzymes which create or break down chemicals in the complex process of cell metabolism, which pump harmful ions out of the cell and useful ones in, and which build cell structures and even repair the DNA itself. They are very basis of life.
Once this step had been accomplished the stage was set for the first forms of life observable today – the bacteria. A bacterium has a DNA chromosome which synthesises the proteins with the help of RNA, and a cell membrane and wall to keep the living material separate from the environment. On some counts bacteria are the most successful life forms on the planet, inhabiting almost all known environments from the edge of space, to the Antarctic, volcanic pools, the deep sea, and as confirmed recently, the deep earth, kilometres below the surface. Fossils of bacterial colonies first appear in the record just less than 4 billion years ago. They were the dominant life form for the next 2 billion years.
Cellular mitochondria originated in separate organisms
The next stage, around 2 billion years ago, was the emergence of more complex, but still single celled, organisms such as amoebae, algae or yeasts. It is now accepted that this happened by the co-operation and interpenetration of different forms of bacteria. The idea was first put forward by American biologist Lynn Margulis in the 1970s, based on earlier Russian work. Margulis’ Theory was that a large bacterial cell had formed a partnership with a small energy-producing bacterium, akin to modern purple non-sulphur bacteria, so that eventually neither could live without the other. Eventually, the smaller cell took up residence in the larger cell, and we see the descendants of these small energy producing cells inside each cell of modern animals, plants and fungi in the form of mitochondria.
In the case of plants, these two partners were joined by a third type of bacteria, closely related to modern blue-green algae, which was capable of photosynthesis. Proof of this partnership, or symbiosis, is the fact that both mitochondria and the photosynthetic components of plant cells, chloroplasts, retain their own separate DNA.
For a further billion years, life on earth was restricted to bacteria and single celled plants, animals and fungi. However, at a certain stage, the single celled organisms began to associate with each other into colonies and strands similar to those we see in modern jellyfish, sponges and sea-weeds, and around 500 million years ago true multi-cellular animals and plants can be seen in the fossil record. The exact mechanism is still obscure, but in what is termed the ‘Cambrian Explosion’ most of the modern families of plants and animals burst onto the scene.
Darwin himself admitted that the Cambrian Explosion posed the greatest difficulty fir his theory of gradual evolution – it simply does not seem to fit with the facts. Smith and Szathmary speculate that the drastic change in earth’s atmosphere due to the production of oxygen by algae may have allowed larger animals to survive, or else the ‘division of labour’ by the different tissues of multi-cellular animals drove their explosive evolution. Other scientists believe that a process of hybridisation between the different animal groups lay behind the sudden appearance of insects, worms, molluscs, crustaceans and vertebrates. One thing is certain – it was no gradual process.
Once multi-celled organisms had evolved there was a further transition from reproduction by simple budding or cloning to reproduction by sexual means. This may have evolved once but more likely several times as not all animals, plants and fungi are sexual, and many can use either method. For instance, amongst green fly some species are asexual, some are sexual and some reproduce by cloning in summer when food is plentiful and turn to sexual reproduction as autumn approaches. Turkeys can occasionally reproduce asexually and recently a lonely Komodo Dragon in Chester Zoo produced young with no male present. Asexual reproduction is seemingly the less complex and difficult process but the population will lack genetic diversity and be vulnerable to disease and less adaptable to changes in the habitat.
Once multi-cellular life had evolved Smith and Szathmary trace two further major transitions. The first is that of the social insects which has evolved separately on at least three occasions – termites, bees and wasps, and ants. In many ways the insect colony behaves like one super-organism with sterile workers dividing the work of gathering food, defence and care of the young for the benefit of a single queen.
Transition to human society
The final transition they trace is the transition to human society. It is here I part company with their analysis. They see speech and language as the crucial development but I would see the development of a mode of production as the unique characteristic of human society. In The Role of Labour in the Transition from Ape to Man, Engels describes animals as having a “mode of being” contrasting with a human “mode of production”. Of course speech will have been closely linked with the adoption of a mode of production but I think here Engels was closer to the reality than even Smith and Szathmary.
It seems strange to think that for three quarters of earth’s history, billions of years, there was no life- form on the planet more advanced than slime. But even slime has cells with an amazing and interlinked cycle of metabolism and self-sustaining biochemical activity which is still only superficially understood by modern science.
Major Transitions in Evolution explains this very well and strikingly verifies the theoretical framework outlined by Frederick Engels in Dialectics of Nature over 140 years ago but on a much higher plane of facts and evidence. Each of the transitions is a dialectical transformation of quality into quantity; we see an interdependence of opposites in the derivation of single celled animals, plants and fungi from simpler bacteria; also the whole is greater than the sum of its parts in the case of multi-cellular animals and plants, and also in the social insects and human societies[FA1] .
Major Transitions is well worth reading by any socialist with an interest in dialectics or biology. They also wrote a shorter book The Origin of Life which covers much of the same ground but in a more accessible format.
January 9, 2019
