I suppose fear of death could be cited near the top as every living organism's basic instinct since the creation of life at unicellular level. According to Robert Anton Wilson's 8-circuit model of our brain, the first and most basic circuit is the oral bio-survival circuit which concerns the preservation of life at all costs. For this reason, when circumstances are so threatening as to endanger one's life, it will get ahead of all other circuits to take action, to cite some of them, the anal emotional-territorial circuit (the one concerning who owns what), the time-binding semantic circuit (reasoning) and the moral socio-sexual circuit (moralities, whether it is safe to divorce according to some religion or not). In face of a threat of such magnitude, all the concerns generated by the next 3 circuits will become so obsolete and useless that, the living organism, whatever species it is, will first do whatever it takes to survive. A little scary and unpleasant for our modern ways of thinking, but the pure, universal truth in fact.