Most furry animals look neat, smooth and appealing. Each hair on the animal's surface grows so as to reach the envelope defined by all the others. A tree achieves this effect optically: an overshadowed shoot grows faster. So Daedalus reckons that each hair is an optic fibre, carrying ambient light at its tip down to its growing root. If it is ‘overshadowed’ by the other fibres, it is stimulated to grow. When its tip reaches daylight, growth is turned off. Most animal fur has a visible colour, so the light used must be infrared or deep red. (Thus, despite its obvious camouflage advantages, no animal has green fur; it would absorb the crucial radiation.)

Now human hair must be just as transparent to near infrared. A ruby-red laser treatment can be used to destroy unwanted hair; presumably the massively intense pulse coming down the shaft disorganizes the photosensitive follicle. So why does our hair not grow as neat and smooth as animal fur? Daedalus blames hair-cutting. An uncut hair has a tapered tip, giving a graded match between the refractive index of air and the much higher index of the hair. Radiation enters with little loss — some moth eyes have a micro-spiky surface for just this reason. But a cut hair terminates in an abrupt planar discontinuity, an optical mismatch which reflects away most of the radiation. The root is left permanently in the dark, and the hair just grows uncontrolled. Hair that is seldom or never cut (such as that of the eyebrows) is usually neat and even.

So in barbering, as in much else, once we start interfering with Mother Nature, we are forced to go on doing it. Most of us need endless hair-cutting to avoid looking shaggy and unkempt. Daedalus's analysis provides a neat way out. His ‘Fluorostyle’ hair-spray is an aerosol loaded with an infrared fluorescing agent. Sprayed onto the head, it is absorbed into the most prominent, outer hairs. The fluorescer absorbs visible light, and emits infrared inside the hair; this is transmitted down the shaft and inhibits growth. Shorter, overshadowed hairs are shielded from the aerosol, and grow normally.

Soon the user will have a neat and even thatch. Selective, graded applications of Fluorostyle spray will then shape, sculpt and maintain it to any desired envelope. The happy user will be as smart and trim as our primitive ancestors — whose popular image as shambling, shaggy, matted monsters can now be seen as totally undeserved.