Earthquake

Previos biological analyses dating back to the mid 1970s concluded that an innate (genetically based_ seismic=excape responses was unlikely to have evolved in animals, due to the impression that earthquakes were ÐŽ§ ÐŽK too rare to establish a selective advantage that might permit genetic fixation of such a characteristics,ЎЁ and the question of ÐŽ§whether most species could take successful evasive action even if they had advanced knowledge of an impending earth-quakeЎЁ (Gans, 1976). Both of these concerns need re-evaluation.

A commonly raised objection to the concept that animals might detect earthquake precursors is the fact that the life spans of most animals are much shorter than the typical repeat time of large seismic events. Therefore, they are unlikely to remember any precursory signals. KirschvinkÐŽ¦s argued that animals might be able to detect earthquake because animal behavior is susceptible to genetic control. Kirschvink suggested that through the course of random mutation and natural selection, rare events that kill or reduce the fitness of a species can lead to the evolution of mechanisms to avoid such mortality. Animals also evolve behaviors that enhance survival and fitness, for example the escape responses from fire and predators and many of these behaviors involve sophisticated pattern recognition abilities. A large number of complex behavioral responses of animals are under genetic control. The behavioral genetic systems, like all genes, are under ancient fossils that preserve information that has helped animal to enhance survival and fitness. For example, the complex behaviors like the honeybee waggle dance language are instinctive, appearing spontaneously in the adult worker bees even these bees have never been experienced to the honeybee waggle. The explanation for that is the sensory input through vision, hearing, touch, and smell elicits a ÐŽ§fixed-actionЎЁ response, causing an immediate and essentially involuntary, reflex-like reaction. These responses range from escape responses to mating behavior, and occur in animals as diverse as flatworms, insets, and mammals. The behaviors and response of this sort are not learned, but rather inherited, shaped through the long, slow process of random mutation and natural selection.

In California and many other areas, the great earthquakes occur with average repeat intervals of 100 years or so (Dolan et al., 1995; Sieh, 1996). Although moderate earthquakes affect smaller geographic areas, but they are more numerous and may dominate the local seismic hazard for an area. Zones of high seismic activity have existed on Earth for at least two billion years or more. A small selection pressure acting over a vast interval of geographical time can be just as effective at gene fixation as is stronger selection acting over a shorter time interval.

Second, evasive action can reduce mortality during an earthquake. Earthquake can kill animals or reduce their fitness in a variety of ways, form direct physical shaking (eg. causing burrows to collapse, shaking eggs out of nests, breaking honeycomb, etc) to indirect action of mudslides and tsunamis. Fitness can also be reduced in the interval after an earthquake as a result of disruption in the interval after an earthquake as a result of the disruption of normal behavior from aftershocks. For many animals and organisms, behavioral action taken prior to an earthquake could reduce mortality: fish and cetaceans leaving costal zones, rodents existing from collapsible burrow or dwellings, bees swarming, parent delaying egg-laying, etc.

KirschvinkÐŽ¦s article stems from similarities in the list of possible pre-earthquake behavior to those unusual behaviors which have been reported for animals in the days, hours, and minutes prior to an earthquake. The similarities of behaviors reported by cultures as diverse as those in Middle East, South America, and Asia lead to the hypothesis that a biological earthquake warning or prediction system may exist.

The major process of complex biological systems to evolve is to take an existing genetic pattern that evolved through one function and to link it or adapt it for a different role. The new system is then gradually debugged and improved through the process of random mutation and natural selection. This evolution process is termed as exaptation (Gould and Vrba, 1982). For a seismic-escape response to develop in the process of exaptation, an organism would need to combine an existing escape, panic, or ÐŽ§exit from the burrowЎЁ behavioral pattern with one or more appropriate sensory inputs to trigger the reaction.

Has a seismic escape or ÐŽ§early warningЎЁ response already evolved?

All animals possess instinctive responses to escape from predators and from fire. In human, these responses are known as panic and are associated with the rapid release of adrenaline, which heightens sensory awareness and temporarily blocks sensation of pain. Numerous observations exist of animals displaying panic in the few seconds prior to the onset of strong ground shaking. Tributsch (1982) lists many such examples, including dogs braking, nervous cats jumping out of windows, birds screaming, rats running out of their holes, bees swarming, etc. These observations support that a potential seismic-escape response is present in the behavioral repertoire of animals, and that it can be released at least by the sensory perception of low-frequency vibration. For example, some extant rodents such as California kangaroo rats use low-frequency seismic ÐŽ§footdrummingЎЁ as a method of communication between burrow to mark territorial boundaries and to notify predatory snakes that their presence has been discovered (Randall, 1997; Randall and Lewis, 1997; Randall and Matocq, 1997). As both snakes and rodents have ability to detect and respond to these vibrations, and sensory systems are in general highly conserved, the ability to detect these low-frequency signals was probably present in the last common ancestor of reptiles and mammals. It may well be a primitive feature of all vertebrates. The evolution of vibration from earthquake to trigger seismic-escape response is not difficult to conceive, particularly via the process of exaptation previously described. A cursory survey of the field of neurophysiology demonstrates that predator prey interactions are largely responsible for driving the ability of animals to detect environmental signals. Given the enormous selection pressure of predator-prey interactions, evolution should have perfected the auditory and tactile sensitivity of animals to detect the vibrations from earthquake. Evolutionary exaptation of these senses to yield