Richard Dawkins in The God Delusion ignores symbiosis and The Riddle of Sex in his argument. This is surprising as it has significant implications for his logic.

Symbiosis is defined as a biological relationship in which two species live in close proximity to each other and interact regularly in such a way as to benefit one or both of the organisms. When both partners benefit, this variety of symbiosis is known as mutualism. Where only one partner benefits the arrangement is known as parasitism, a parasite being an organism that obtains nourishment or other life support from a host, usually without killing it. Commensalism is the term used to describe the relationship where only one of the two organisms or species derives benefit, but in this case it manages to do so without causing harm to the host.

We will deal primarily with Symbiosis where both parties to the relationship work together (often seemingly unknowingly) and both gain benefit, that is, mutualism. Of all the objections to the theory of evolution, arguably this phenomenon poses the greatest threat. Evolution through natural selection has for the past one hundred and fifty years dominated the thinking of most evolutionists. Yet, there is change in the wind, not least from the increased awareness of the implications of inter-dependent relationships between species. Darwin himself considered the question when he said in On the Origin of Species:

“If it could be proved that any part of the structure of any one species had been formed for the exclusive good of another species, it would annihilate my theory, for such could not have been produced through natural selection.”

Strictly speaking, of course, Darwin may not have been talking about Symbiosis because he used the phrase ‘exclusive good’, but whatever the interpretation of Darwin’s words, it is clear that the principle of symbiosis presents a formidable challenge to the idea of evolution and particularly to the principle of natural selection.

The best way to consider symbiosis is to look at specific relationships between organisms. Examples of such relationships abound in the natural world. (From Wikipedia)

Consider the goby fish, which sometimes lives together with a shrimp. The shrimp digs and cleans up a burrow in the sand in which both the shrimp and the goby fish live. The shrimp is almost blind leaving it vulnerable to predators when above ground. In case of danger the goby fish touches the shrimp with its tail to warn it. When that happens both the shrimp and goby fish quickly retract into the burrow.

A famous land version of symbiosis is the relationship of the Egyptian Plover bird and the crocodile. In this relationship, the bird is well known for preying on parasites that feed on crocodiles which are potentially harmful for the animal. To that end, the crocodile openly invites the bird to hunt on his body, even going so far as to open the jaws to allow the bird enter the mouth safely to hunt. For the bird’s part, this relationship not only is a ready source of food, but a safe one considering that few predator species would dare strike at the bird at such proximity to its host.

Then there is the case of symbiosis that exists between siboglinid tube worms and symbiotic bacteria that live at hydrothermal vents and cold seeps. This is a mutualistic symbiosis where the worm completely loses its digestive tract and is solely reliant on their internal symbiants for nutrition. The bacteria oxidize either hydrogen sulphide or methane which the host supplies to them. These worms were discovered in the late 1970s at the hydrothermal vents near the Galapagos Islands and have since been found at deep-sea hydrothermal vents and cold seeps in all of the world’s oceans.

Examples of symbiosis in the natural world abound and it is not difficult to see how this phenomenon threatens the theory of evolution by natural selection. How can chance gradations in both species lead to the development of such relationships? Evolution dictates that such things cannot happen.

This is such a serious objection to the theory of evolution that some are prepared to sacrifice the idea of natural selection as the dominant mechanism. The biologist Lynn Margulis, famous for her work on endosymbiosis (an organism or cell that lives within the body of another organism), contends that symbiosis is a major driving force behind evolution. She is not so much concerned with symbiosis at the level of the organism as at the molecular level. Notwithstanding, she considers Darwin’s notion of evolution, driven by competition, as incomplete, and claims evolution is strongly based on co-operation, interaction, and mutual dependence among organisms, most particularly, bacteria. According to Margulis and Dorion Sagan (1986), “Life did not take over the globe by combat, but by networking.” As in humans, organisms that cooperate with others of their own or different species often out-compete those that do not.

Which brings us neatly to the riddle of sex. Margulis and Sagan devote a chapter of Microcosmos to this subject. How has evolution through natural selection tolerated such a wasteful, unreliable and inefficient practise as two-parent sex, when simple cell-replication is available? Margulis and Sagan explicitly state that two-parent sex cannot have been maintained by natural selection:

“But two-parent sex itself was never maintained by natural selection. Indeed, if the evolutionary process can by-pass biparental sex – through parthenogenesis in beetles, cloning in humans, or any other way – and still preserve complex multicellularity, it no doubt will. Biologically, sexual reproduction is still a waste of energy and time.”

Margulis and Sagan argue that two-parent sex had its origin in symbiosis. Two distinct unrelated happenings became interlocked in a feedback loop; the reduction of number of chromosome cells in the nucleus of offspring cells; and cell and nuclear fusion. This latter occurrence involved the mixing of DNA from sources separated in time and space is described as a form of sex. Finally, this mixing of genetic material become linked to reproductive mechanisms and gave rise to biparental sexual reproduction. To a lay person (such as I) this is hard to follow but the point seems to be that the genetic origin of two-parent sex was symbiotic in nature. And why do we require this method of sex instead of the much simpler method of simple cell division? The answer apparently lies in our ancestors, by virtue of the need to swim (), losing the ability to reproduce asexually.

It is evident that Dawkins can gain no solace from these alternative theories. For him, natural selection must be the dominant mechanism for evolution. Otherwise how does he fit the idea of cooperation into his own model? Where does that leave The Selfish Gene? As we have seen, Dawkins has already started to talk in terms of the evolution of ‘evolvability’. What further ground will he be forced to give? In fact, as we will see later, this is not the challenge for Dawkins that we might have expected. We discuss in a subsequent section his creation of the meme, which is the perfect example of his bending his own rules when it so suits.