Nor is it clear what value discordance might be involved. We could come up with one, though.If one theorized that modafinil came with a memory penalty, inasmuch as memory consolidation and the hippocampus seem to intimately involve sleep, then we might have a discordance where we value being able to produce and act more than being able to remember things. This might even be a sensible tradeoff for a modern man: why not sacrifice some ability to learn or remember long-term, since you can immediately gain back that capacity and more by suitable use of efficient memory techniques like spaced repetition?
#1 seems promising. Like piracetam, there is something in short supply that modafinil would use more of: calories! While you are awake, you are burning more calories than while asleep. During the day, synapses build up levels of some proteins, which get wiped out by sleep; is this because synapses and memories are expensive38 and cannot be allowed to consume ever more resources without some sort of synaptic homeostasis? Fly & rat studies bear out some of the predictions of the model and may lead to interesting new findings39 (see also Bom & Feld 2012 discussing Chauvette et al 2012).
Previously noted was the metabolic cost of defending against infections; one animal study found the proximate cause of death in sleep deprivation to be bacterial infections40. You are also - in the ancient evolutionary environment - perhaps exposing yourself to additional risks in the dark night. (This would be the preservation & protection theory of sleep.)
Although it only accounts for 2% of an adult’s body weight, it accounts for 20-25% of an adult’s resting oxygen and energy intake (Attwell & Laughlin 2001: 1143). In early life, the brain even makes up for up 60-70% of the body’s total energy requirements. A chimpanzee’s brain, in comparison, only consumes about 8-9% of its resting metabolism (Aiello & Wells 2002: 330). The human brain’s energy demands are about 8 to 10 times higher than those of skeletal muscles (Dunbar & Shultz 2007: 1344), and, in terms of energy consumption, it is equal to the rate of energy consumed by leg muscles of a marathon runner when running (Attwell & Laughlin 2001: 1143). All in all, its consumption rate is only topped by the energy intake of the heart (Dunbar & Shultz 2007: 1344).
There are additional disadvantages to increased intelligence - larger heads would drive maternal & infant mortality rates even higher than they are42. And it’s worth noting that while the human brain is disproportionately huge, yet the human cerebral cortex is not any bigger than one would predict be extrapolating from gibbon or ape cortex volumes, despite the human lineage splitting off millions of years ago.43 The human brain seems to be special only in being a scaled-up primate brain44, with close to the metabolic limit in its number of neurons45 (which suggests a resolution to the question why despite convergent evolution of relatively high intelligence46, only primates
took off). There are other ways in which humans seem to have hit intelligence limits - why did our ancestors’ brains grow in volume for millions of years47, only to come to a halt with the Neanderthals48 & Cro-Magnons and actually start shrinking49 to the modern volume, and why did old age only start increasing 50,000 years ago or later50, well after humans began developing technology like controlled fire (>=400,000 years ago51); or why are primate guts (also resource-expensive) inversely correlated with brain size & in one fish breeding experiment, or muscles starved of sugars and brains favored52; or why do the Ashkenazi seem to pay for their intelligence with endemic genetic disorders53; or why does evolution permit human brains to shrink dramatically with age, as much as 15% of volume, besides the huge performance losses, while the brains of our closest relative-species (the chimpanzees), do not shrink at all?54 For that matter, why are heads, central nervous systems, and primate-level intelligence so extremely rare on the tree of life, with no examples of convergent evolution of intelligence (as opposed to examples like basic eye-spots, which are such a fantastically adaptive tool that they have independently evolved
somewhere between 45 and 60 times)?55
The obvious answer is that diminishing returns have kicked in for intelligence in primates and humans in particular5657. (Indeed, it’s apparently been argued that not only are humans not much smarter than primates58, but there is little overall intelligence differences in vertebrates59. Humans lose embarrassingly on even pure tests of statistical reasoning; we are outperformed on the Monty Hall problem by pigeons and to a lesser extent monkeys!) The last few millennia aside, humans have not done well and has apparently verged on extinction before, and the demographic transition60 and anthropogenic existential risks suggest that our current success may be short-lived (not that agriculture & civilization were great in the first place). Some psychologists have even tried to make the case that increases in intelligence do not lead to better inferences or choices (Hertwig & Todd 2003).
Modafinil or modafinil-like traits might be selected against due to increased calorie expenditure, decreased calorie consumption, or risks of night-time activity. Either explanation fails in a modern environment; modern societies have murder and assault rates orders of magnitude lower than that seen among aborigines61, and calories are so abundant that they have begun reducing reproductive fitness (we call this poisoning-by-too-many-calories the obesity epidemic).