Ingenious Genes: How Gene Regulation Networks Evolve to Control Development

Chapter 5. Why Gene Regulation Networks Are the Controllers of Development

5 Why Gene Regulation Networks Are the Controllers of Development Consider a scene that took place on the banks of the Hydaspes River in the Punjab region of India in 326 BC. Nearly 50,000 infantry, more than 10,000 cavalry, and 200 elephants were involved in intense activity that resulted in more than 15,000 deaths. In order to make any sense of what occurred, it is necessary to understand who was controlling what was going on. It turns out that the forces that began on the right bank of the river, under the command of Alexander the Great, were battling the forces of the Punjabi King Porus, which were lined up on the left bank to repel any crossing. In response, Alexander had his forces carry out a pincer maneuver . Alexander led a small group of his forces 17 miles upstream. If Porus sent too many of his men upstream, Alexander’s General Craterus would lead the bulk of his army across the river. Instead, Porus sent too few men to repel Alexander’s crossing, and they were overwhelmed. Alexander was then able to bring all of his forces across the river. When the two complete forces later met, the Macedonian forces were ultimately able to surround the Indian forces after the Macedonian cavalry outflanked and circled behind the Indian lines. The great achievement of this maneuver was that it minimized the exposure of the Macedonian cavalry to the Indian war elephants, which was important because just the smell of the elephants scared the horses (Fuller 1960; Plutarch 75). Understanding such a battle requires identifying who was in control and what that person was trying to do. Without that information, we would see only a whirling confusion. Biological development, particularly the development of complex organisms, is an enormously complex dynamic process. In order to understand such a system, it is crucial to understand the controller of that system. Just as understanding control offers insight into the activity that 98 Chapter 5 took place on an ancient battlefield, so too can understanding control offer insight into the activity that is biological development. Searching for the controller of development requires investigating both the notion of control and the process and evolution of development. Different types of systems fall under different types of control. Military control is relatively clear and well understood. In many uniforms, the crucial information about control relationships is literally worn on one’s sleeve. In this chapter, I will investigate various types of control with the goal of understanding the control that is exhibited in development. I will identify a new extrinsic concept, design-control, and suggest that gene regulation networks are the controllers of development. This argument will rely on the empirical fact that gene regulation networks are highly adaptive evolved systems. In chapter 4, I provided an explanation for the adaptivity and evolvability of gene regulation networks that rested on the connectionist framework. Thus, I will argue that the connectionist framework for gene regulation networks explains why gene regulation networks are the controllers of development, and why understanding gene regulation networks is crucial to understanding development. 5.1 Causal Control Philosophers typically discuss the concept of control as it pertains to actions within the context of action theory. For example, in her investigation of how to apply reasons to animals, Susan Hurley (2001, p. 424) defines control as “the maintenance of a target value by endogenous adjustments in the context of exogenous disturbances.” I shall begin my investigation of control by analyzing this definition. To say that system C is under control relative to target value T of variable V is to say something about the process involving the system C and its environment that determines the value of V. In particular, changes in V from T due to changes outside system C are counteracted by changes within system C that return the value of V to T. I call Hurley’s notion of control causal control. The notion of causal control is metaphysically lean. It places no restriction on what counts as a target value to be maintained , as an endogenous change, or as an exogenous disturbance, or on how the system and the environment are distinguished. This lack of conditions leaves the concept simple and flexible. The only metaphysical Why Gene Regulation Networks Are the Controllers of Development 99 extravagance comes in the holistic nature of the...