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ii.
Generation by man.
Uniqueness in manmade items is acquired in a
slightly different manner. The first objects crafted by human hands were all
different from each other. As hard as a craftsperson might try to produce 10
clay pots of the same size and shape, limitations in hand production will
always preclude absolute uniformity. Because hand-formed objects have
become increasingly rare, they are now more expensive than their machine
counterparts, and we value their uniqueness. Over the last century, machine
production of all types of things has become both common and expected.
Items produced by machine are more uniform and mass production has
reduced their cost. However, for the criminalist, this means that it is becom-
ing harder and harder to, for example, identify individualizing characteristics
in two synthetic fibers that have just come through the holes of a spinneret,
or two screwdrivers that have just come out of a forge or stamp. For mass-
produced items, individualizing characteristics are acquired mostly by use,
wear, or exposure to different environmental conditions. For example, shoe
soles acquire unique gouges and cuts as they are worn; the screwdriver may
acquire indentations and deformations from both intended and unintended
use.
 
iii.
Entropy and disorder.
In Chapter 4, we introduced the idea that indi-
vidual traits are a direct consequence of entropy, the tendency of the universe
to move toward disorder. Order is imparted during the manufacture of an
object, whether it is a plant making cocaine or a machine making a gun
barrel. Objects made in the same way will acquire comparable characteristics;
these are 
 
class characteristics
. The level of similarity depends on the amount
of control exerted during manufacture. The less control that is exerted over
the manufacturing process, the greater the dissimilarity allowed, and on a
larger scale. Tool machining is a good example. A slotted screwdriver need
only be flat and fit into the head of a slotted screw. Fairly large tolerances
are acceptable for this purpose. The existence of microstriae does not affect
its primary performance as a screwdriver, nor do even minor imperfections
in the edge. For this reason, no attempt is made to control the microappear-
ance of the edge or the number or placement of microstriae. Because of mass
production, lots of screwdrivers will initially look quite similar, even at the
level of microcharacteristics (Murdock and Biasotti, 1997). However, the
moment the tool is machined, it begins to diverge from all other similar
screwdrivers. Unless it is a magical self-repairing screwdriver that can violate
the second law of thermodynamics, disorder begins to result from use (gauges
and dents) or even simple existence (rust and dirt). This disorder manifests
as individual characteristics.
Let’s take this a step farther and consider the fate of this same screwdriver
and a pry mark made with it in a door frame. The moment the pry mark is
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made, the characteristics of the screwdriver and the pry mark each begin to
diverge as entropy takes its toll. This relates directly to our ability to match
the screwdriver to the pry mark. If the mark was made recently, a reference
mark made by the same screwdriver will look quite similar to the evidence
mark, allowing ready assignment of both to the same source, the screwdriver.
If the mark is only detected after a year has passed, its relation to a reference
mark made by the same screwdriver may be less readily concluded. Not only
has the pry mark been subject to change, but, depending on the circum-
stances, so has the screwdriver. After a year, it might only be possible to
compare class characteristics, expanding the possible sources of the pry mark.
In extreme cases, even the class characteristics may have changed, resulting
in either an inconclusive determination or a false exclusion.