The simple fact is that our brain does a lot of work throughout a day, and, in its standard operation, waste materials build up that, in large enough quantities, cause dysfunction or, when pushed to extremes, damage of the brain. During sleep, the space around our neurons and glial cells expands, and, as I understand it, the postulated function of this is to permit better flow of cerebrospinal fluid through our brains and thus flush them of waste material. I had mammalian sleep explained to me this way by an Anatomy and Physiology teacher - quite simply, sleep is not something that our brains can go without, and a properly functional brain (that is properly producing melatonin) sets and enforces a pretty strict circadian rhythm wherein we are awake during the day and asleep during the night. That is not to say that we are not capable of flexibility in this regard, but pushing our limits in regards to sleep is not a healthy practice.
Natural selection tends towards favoring the individuals in a population that display traits that make them superior survivors and reproducers within the population's environment - while you say that it would tend towards individuals who were capable of maintaining proper function without sleep, I would argue that sleep is a sort of built-in necessity of our complex and highly developed brains and that proper function of our brains can not be maintained without it. I would hypothesize that any individuals that were born with genetic traits that incapacitated or limited their ability to sleep (i.e., genetically induced insomnia) would be at a pretty extreme disadvantage compared to other members in the population. Although there are many nocturnal predators, none have been enough of a threat to our species that it has limited us in any significant or tangible way, and nor have any of them become so well adapted that they regularly threaten or prey upon us while we sleep.
Natural selection does not do much in the way of acting on neutral traits - neutral genetic traits tend to remain relatively consistent in a population as long as the environment remains relatively consistent such that, relative to the environment, those traits do not become particularly advantageous or disadvantageous. While there are exceptions wherein extremes are favored, it seems clear that any disadvantages posed by sleeping at night (in regards both to our modern species and our ancestors) are far outweighed by the advantages of being fully alert and functioning during our regular operational hours.
While it's true, that's why most people in ye olde times would awake about 1 am (gone to bed at 8 pm) have a snack and go back to bed.
Additionally there was also after snack siesta (we had those on Sunday afternoon).
In primeval times, having a brief pause relaxing in the tree after lunch seems like good way to prime you for sleep later in the evenings.
Sleep isn't a luxury, it's a necessity, necessary for our brains to defrag. Saying sleep is luxury is like saying eating isn't a necessity for survival.
As someone that at one point did trade day and night, I can tell you I was plagued by heart palpatations and general feeling of unease even after switching to 8hrs of sleep during day.
Our species has evolved for at least 50 million years to sleep on tree tops in nests for the full night within a colony, viz all higher primates and many lesser ones all the way down to Lemurs. The homo genus, where we have evidence, has shown exactly the same patterns of sleep as modern humans. And add to that the last 400,000 after the invention of fire where any modern camper wouldn't have felt out of place inside any group of proto-humans.
And there never were any other primates, or trees either.
In a lab based on extreme experimentation, there is no substitute for perseverance until a breakthrough is achieved. Even if you don't start out trying to emulate Edison, you end up that way.
In chemical research you don't just turn off the terminal when it gets dark outside and call it a day.
I never thought it was the least bit unusual that every grad student's lab had a cot near the desk. You really aren't going to get anything monumental done if you go home from work every single day.
What happens if you have a 36-hour experiment that must be carried to completion, or a client's chemical tanker at the dock for a brief 36-hour stay where they are loading or discharging products that no one else can handle either?
You wait a whole month for your ship to come in, what are you going to do, be too tired to finish the job?
What hurts your productivity more is the chemical toxicity much more than sleep irregularity. In the industrial chemical world, there is more effort to avoid exposure the more toxic a material is, so it ends up being those things which are intentionally ingested that compromise performance.
Caffeine, alcohol, tobacco, and drugs are going to make you much more tired than you would be without them.
dano