Mantis shrimp are are colorful little critters. Especially in their own eyes.

Animals are able to perceive color because the eyes contain different types of light-sensitive cells, or photoreceptors, each of which is most sensitive to a different part of the visible-light spectrum. Human eyes have three such photoreceptors, with a peak sensitivity to greenish, blueish, and reddish light. (There is also a fourth type of photoreceptor, which is used mostly for peripheral vision, and vision in darkness.) In other words, humans are trichromatic. The tri in trichromatic doesn’t mean that we perceive only three colors, but that all colors that we perceive can be reduced to a mixture of three colors (see also my post on color vision).

Most other mammals, as well as colorblind humans, have only two types of photoreceptors for color vision, and are therefore bichromatic. Most birds, on the other hand, are tetrachromatic (i.e. four photoreceptors for color vision), and therefore have a slightly more colorful visual palette than we do. But the variation between species is relatively small: Most animals have two to four types of photoreceptors for color vision. And there is good reason for this evolutionary agreement: Two to four photoreceptors are all that is needed to capture the colors that are actually present in the environment. Adding a fifth photoreceptor does relatively little to improve color vision.

Source: National Geographic

But the Mantis shrimp is a remarkable exception. This coral-reef-dwelling crustacean is endowed with 12 to 21 different types …

The eye is a jelly-filled chamber with a lens in front of it. This lens focuses light onto the retina, in the back of the eye, from where nerve impulses are sent to the brain. But the eye’s lens is an imperfect device. For example, different colors have different focal lengths. This means that if you focus on the blue stripe of Newman’s Who’s Afraid of Red, Yellow and Blue, the yellow and red stripes will be ever so slightly out of focus. This and other types of distortion are most pronounced for large lenses, so it is best to keep the surface of the lens as small as possible. For this reason, most of the eye’s lens is covered by the colorful iris, which serves more than just an aesthetic purpose. And the part that is not covered by the iris is your pupil.

Who’s afraid of red, yellow, and blue?

But there is also downside to having small pupils: They don’t let a lot of light through. This doesn’t matter when you are in a bright environment where even tiny pupils let through sufficient light. But in darkness small pupils simply won’t do: Optical distortions or no, in darkness pupils must increase their size in order to let through the bare minimum of light that is required for vision.

So there are two opposing forces that together determine the size of your pupil. On the one hand, small pupils suffer …

Like workers from all trades, scientists produce things. Bakers produce bread, construction workers produce buildings and such. And we scientists… well, we produce p values that are smaller than .05.

So what exactly is a p value? If a scientist wants to prove a point, she generally does so by testing a hypothesis. For example, she might hypothesize that rich people are happier than poor people. She could test this hypothesis by collecting happiness ratings from fifty rich and fifty poor people, and calculate a p value for the difference. The p value then expresses the chance that these happiness ratings would be as different as they are, or more different, if rich and poor people were really just as happy. (For a more detailed discussion, see my previous post.)

Are you still with me? Maybe not, but no matter: The important point is that a low p value means that your hypothesis is probably correct. (Actually, it means that the data is unlikely given the null hypothesis, but let’s skimp over this important detail for now.) The commonly accepted threshold is .05: If your p value is below .05, you have found something worthy of publication, otherwise you haven’t.

So there is a clear incentive for scientists to find p values that are smaller than .05. So what do yo do if you get a p value of .051? Well, you do what any sensible scientist would do: You test a few more participants, analyze the data …

The first journal purely dedicated to science was the Paris-based Journal des sçavans, founded in January 1665. The London-based Philosophical Transactions of the Royal Society was founded two months later. The Journal des sçavans appears to have died a fairly quiet death in 2007. But the Philosophical Transactions is still around, is still prestigious, and still publishes papers in pretty much the same way as it has done for centuries. I published a paper there myself not too long ago.

When these journals were founded, they provided an excellent platform for scientists to share their work. Science was mostly a regional affair, and very few people were wealthy enough to engage in the leisure of science. And, of course, there was no internet. In this small analog world, papers were the best form of communication.

Things change, though.

Some time ago I wrote about a dataset that I had downloaded from PubMed, which is a more-or-less comprehensive database of scientific articles. I downloaded information about only 38 journals, but even from this small selection it is clear that papers are being published at an exponentially increasing rate, and that this trend has been going on for some time.