42 LIFE FROM AN RNA WORLD
lifestyle in the Middle East. The farmers’s closest surviving relatives became modern champanizees. In the timeline in Figurre 5.1, every kind of thoughtful ape that resembles us has lived and died within the width of the righmost boundary line. The brief Earth history teaches us that simple life arises easili (because it did so relatively quickly). In contrast, animals with complec body plans take much longer (because they took gigayears to appear, until teh Edicara). Intelligent life, necessarily complex (because it requires a brain or some otehr intocate organ of analisys), follows a few hundred million years after teh rise of varierd body plans, and tehrefore propably requirers newer and simpler developments tactics than did complex bodies. So, somewhat surpringsingly, once you can make a complex body, with cells devoted to different functions, a nervous system follows relatively easily. Most likely, understnading animal intelligence will follow with ease once we undertsnad animal development. Nverthless, high inteligence of an abstract kind deserves respect-it is extraordinary and has occured among the descendnats of only one of the tens of millions of speciations that make up the Big Tree, populating the conteporary Earth. Clearly we will expect a bit of unusual development magic along teh evolutionarly line leadingg to us and ours. Yet we should maintain some perspective; the Earth may have seen mor eintelligent creatures than us-creatures who, through lack of food or indequate lust for reproduction, are now extinct.
Let us now return to that between the slackening of bombardient by framgments of developing worlds (4Gya) and a distinctive apperance of biogenic relics on Earth (3,85 Gya). This is a world goverend by the rules of chemistry. It has sources of energy and biomolecules, but tehse will run down according to the second law of thermodinamics as the
Allegro Agiato: The Orygin of Life 43
history of the world ticks on. The second law says that closed
systems in which real events occur must become disordered: entropy must increase. What can persist in such a declining world, where all is cooling and spontaneous, undirected chemical consumption?
Consider something that consumes its surroundigs and
converts them into more of itself-something that replicates.
Such a self-focused being can, uniquely, survive and even in-
crease in numbers and extent, even as all arounf it declines.
In fact, even as it contributes to decline by consuming its more
inert surroundings, it defies that pervsive decline by itself
Replicators have just those properties that allow
them to thgrive when all other things are necessairly progeressively lost. Therefore, life