How the ancients slept

No, this is not a blog post about H. P. Lovecraft or his work. It is about how people used to sleep, a story I picked up from the BBC. It is a story that showed me how much I take for granted certain things, like our way of sleeping.
Historian Roger Ekirch from Virginia Tech has shown with sources as far back as Homer that people used to sleep in two periods each night, with a period of activity or contemplation in between. Many sources refer to this as the first and second sleep, and it appear to have been perfectly ordinary to people before the enlightenment.
In a way it makes sense, at a time when artificial light was expensive you went to bed at dusk slept for a while, got up to do some chores, talk to your family, or pray in the middle of the night, after a while you went back to sleep and slept until morning.
There is also empirical research regarding sleeping patterns that cooperate that this divided sleep is natural to people. There are experiments that have been performed by Thomas Wehr and also anthropological studies of populations living without artificial light. It is also stated that this way of sleeping can be found in other mammals.
The artificial light we now take for granted has a rather short history, Paris became the first city with street lights in 1667. (I wonder if that might have anything to do with Paris being know as La Ville-Lumière) It became easier and easier for people to occupy themselves after dusk and the industrial revolution made sure that even sleeping had to be done efficiently without brakes.
This research give ample fodder for speculation. Are people who experiences problems sleeping just trying to sleep the way nature intended for them? Some people have been reported to sleep only a few hours each night, usually you here this about very productive people, might they have slept at other times in addition to their reported nightly sleep? And how screwed up is my sleep pattern if this is the way we are supposed to sleep?
For people who wants to learn more there is a book by Ekirch: At Day's Close: Night in Times Past I am considering getting it, but I already have a few books.
Other sources are:

THOMAS A. WEHR In short photoperiods, human sleep is biphasic, Journal of Sleep Research, 1992 (1) 103-107
Roger A. Ekirch Sleep We Have Lost: Pre-industrial Slumber in the British Isles, American Historical Review, CV, no.2 (April 2001), 343-387

2 + 2 does not equal 3

The human mind is not as rational as we tend to assume from the inside of our own mind. I stumbled across this fascinating example of flawed thinking the other day. Or perhaps it is more fair to label this as a case of flawed estimation than flawed thinking.

A lot of people are concerned with their weight but resent research find that the people most concerned are less skilled at estimating the calorie content of dishes under certain conditions. The different conditions where an unhealthy dish by itself or together with healthy food.
Simple logic would suggest that more food implies more calories but those who estimated the number of calories in the meal rated the options with additional healthy food to have less calories than the unhealthy part of the meal by itself.

More about this research can be read in this paper:
A. Chernev / Journal of Consumer Psychology 21 (2011) 178–183

The people involved in the test where divided into groups and shown different meals and asked to estimate the number of calories. Some rated themselves to be very concerned with their weight and others less concerned. Averaged over the different dishes and groups the people not concerned with their weight estimated the number of calories for the unhealthy dish to be 684 and 658 with the added healthy food item, that is a difference of -26. But the people concerned about their weight estimated the unhealthy option at 711 and the healthy one (more food) at 615, that is a difference of -96.

Even if this research concerns peoples estimation of caloric content of food I would not be surprised if it can be transferred to other areas. How we think should not vary that much with what we are trying to estimate. The explanation that has been put forward for why people make these mistakes is that when you divide something, in this case food, in categorise of good and bad your ability to estimate the combination of them is hampered by to what degree you tend to divide things into good and bad. Many diets are of the kind that they divide foods into categories of good and bad.

It has previously been assumed that concerned people and thus motivated, are less likely to make mistakes. This research has shown that the weight concerned make larger mistakes in estimating caloric content and that is very interesting.