A knockout blow for evolution turns out to be nothing of the sort
AS JBS Haldane famously said, God must have an inordinate fondness for beetles, he made so many of them. Of all the tens of thousands of the horny-winged horde, the creationists have chosen, as the absolute knockout anti-natural selection example, the bombardier beetle. Only the great Organic Chemist in the sky could have designed the chemical weapon system which enables this beetle to deal with ants and other predators.
The special feature is a sac containing a mixture of two chemicals, which do not react with each other spontaneously. When danger threatens the beetle is able to initiate changes in this mixture which cause it to be expelled explosively. The resulting missile is not only toxic and corrosive, but also, because of the heat generated by the reaction, it is boiling hot. Some species adopt a blunderbuss or scattergun method of discharging their weapon, others are even cleverer and can aim at their target like a marksman.
To understand why creationists have been so excited, and to follow the suggested evolutionary pathway leading to this phenomenon, we must look more closely at the chemistry of the process. The storage sac contains two substances, hydrogen peroxide and a relatively simple organic compound, quinol. The latter is oxidisable to quinone, but, although hydrogen peroxide is an oxidising agent, the two can coexist without reacting if left undisturbed. When danger threatens, the sac containing this mixture is emptied into a reaction chamber containing the enzymes catalase and peroxidase. The catalase decomposes the hydrogen peroxide almost instantaneously into water and oxygen, and the peroxidase causes it to react with the quinol, oxidising it to quinone. This in turn causes two things to happen; the heat released in this reaction raises the temperature to boiling point, and the sudden release of gaseous oxygen forces the liquid out with great force. In passing, we note that the creationists have the chemistry and sequence of the process wrong, but, as is their wont, they persevere in their error after being corrected.
Why have the creationists seized on this as a clincher for their belief? Well, it’s all so complicated, isn’t it? Quantities of two unusual chemicals, two enzymes, as well as the anatomical arrangements. Each is necessary, the system would not work if any one was missing. In modern creationist jargon, it is irreducibly complex. Therefore dear old Bomby must have been intelligently designed, mustn’t he? No. It ain’t necessarily so! A plausible sequence leading from a generalised arthropod to this specialised animal can be suggested. It nicely illustrates the way features with one function can be co-opted for other purposes, and demonstrates how small steps, each conferring a minute selective advantage, can lead eventually to large changes. We can note first that each of the four chemicals is not unusual, as claimed by creationists, but is a common constituent of arthropod metabolic systems. Quinone is made by numerous insects; it ‘tans’ the cuticle making the exoskeleton more or less rigid and dark in colour. Quinol may be synthesised by a similar route; it is not confined to bombardier beetles. Hydrogen peroxide is widespread in nature as a product of oxygen metabolism. Catalase and peroxidase are also found universally in the animal kingdom; oxygen, on which our life depends, is not an unmixed blessing, and these enzymes destroy dangerous by-products of oxygen metabolism (think anti-oxidants). Greater gene activity, leading to the biosynthesis of increasing amounts of these chemicals, seems an obvious pathway of natural selection. M Isaak (2003) has linked this process to the anatomical changes which would have taken place concurrently with the chemical developments. Each step in this scheme confers an obvious advantage and so would be selected for. Though the combination of features makes the bombardier beetle unique, individually they have counterparts in many other insects; for example, the secretory glands which produce the pheromones and other chemical signals. Isaak’s article discusses the issue in more detail, and is recommended (Isaak, M. Bombardier beetles and the Argument of Design www.talkorigins.org/faqs/bombadier).
This article was suggested by my reading The Bombardier Beetle’s Chemical Defence, by Marten J ten Hoor, Hoogezand, Netherlands, in CHEMNZ, no. 100. I am grateful to Mr ten Hoor and the editors of that journal for providing that stimulus.