A better argument is presented by this excerpt from that book.
> humans likely evolved to co-sleep as families or even whole tribes, not alone or as couples. Appreciating
this evolutionary context, the benefits of such genetically programmed variation in sleep/wake
timing preferences can be understood. The night owls in the group would not be going to sleep
until one or two a.m., and not waking until nine or ten a.m. The morning larks, on the other
hand, would have retired for the night at nine p.m. and woken at five a.m. Consequently, the
group as a whole is only collectively vulnerable (i.e., every person asleep) for just four rather
than eight hours, despite everyone still getting the chance for eight hours of sleep. That’s
potentially a 50 percent increase in survival fitness. Mother Nature would never pass on a
biological trait—here, the useful variability in when individuals within a collective tribe go to
sleep and wake up—that could enhance the survival safety and thus fitness of a species by this
amount. And so she hasn’t.
Thanks for giving me the inspiration to read it. This book is just fantastic.
> humans likely evolved to co-sleep as families or even whole tribes, not alone or as couples. Appreciating this evolutionary context, the benefits of such genetically programmed variation in sleep/wake timing preferences can be understood. The night owls in the group would not be going to sleep until one or two a.m., and not waking until nine or ten a.m. The morning larks, on the other hand, would have retired for the night at nine p.m. and woken at five a.m. Consequently, the group as a whole is only collectively vulnerable (i.e., every person asleep) for just four rather than eight hours, despite everyone still getting the chance for eight hours of sleep. That’s potentially a 50 percent increase in survival fitness. Mother Nature would never pass on a biological trait—here, the useful variability in when individuals within a collective tribe go to sleep and wake up—that could enhance the survival safety and thus fitness of a species by this amount. And so she hasn’t.
Thanks for giving me the inspiration to read it. This book is just fantastic.