Travel Reference
In-Depth Information
Scientists who are interested in reconstructing the past lives of ancient
organisms by studying form and function recognize three ptimaty factors that
must be considered in interpreting biological sttuctutes. First, and most ob-
vious, are the functional considerations: Just what does this structure
do
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Most biological structures yield some obvious clue. Wings are clearly for fly-
ing, fins for swimming, legs for walking. But sometimes things get far more
complicated. Some structures are not as we would imagine them to be to ful-
fill some obvious function, whereas others share a function, or perform two
or more tasks, and thus become compromises in form. Take the gills of clams,
for instance. Gills first evolved for respiration; they ate used to exttact oxy-
gen from sea water. But in some clams, gills ate also used for feeding. The
same structute now has two functions. It is optimal for neither but, by doing
both jobs, serves its owners well.
Other structures seem incomplete, only partially useful, or so woefully
inefficient as to be laughable. Why do we have appendixes and wisdom
teeth, for instance? Some structures have no obvious function at all. Intet-
preting task, then, is not enough to explain why some organs or biological
structures have the anatomy that they show. Yet evolution, which shapes all
life, rarely produces wasted organs or structures. Perhaps more than simple
function is at work here.
The second factor that influences function is telated to constructional
aspects. Organisms have a very finite suite of material they can build with.
There is no Teflon, or WD 40, or duct tape, or stainless steel, or a million
other human-made building materials in the animal and plant worlds. Some
biological structures have to be made of material less than optimal for their
function and are "designed" (have evolved) accordingly. Our teeth, for in-
stance. They wear out, they are made of a mineral (apatite by name) that
abrades and is attacked by decay over the years. Why didn't we evolve stain-
less steel teeth, which would be far superior? The answer is obvious. Our bod-
ies can secrete the mineral apatite, but they cannot produce steel.
Finally, any biological structure must be viewed from a historical per-
spective. Evolution is like a river, and although it can eddy, the river even-
