A Seal of Approval - 4
Last time we saw some of the adaptations, or alterations within kinds of seals, e.g. of an organ, by which seals are enabled to function most efficiently in their environment.In a similar way mankind has adapted wheeled vehicles, powered by the internal combustion engine, for use in various circumstances. An ordinary roadworthy automobile is generally more than sufficient for use by the civilian operator.
- But for use by certain branches of the police, an ordinary car must be modified with a specially designed police package. The designer, with a good knowledge of automotive engineering - and with input from an experienced driver - has expended mental effort to prescribe a series of modifications to that car. His efforts have been directed towards the goal of producing a vehicle with superior power, manoeuvrability and safety features by the addition and/or replacement of various operational parts in the original car.
In many other cases it is necessary to produce the required vehicle directly from the start - grader for levelling the ground in road-making, tanker truck for transporting milk and fuel, scissor lift to raise workmen high above the ground. Each vehicle has been designed for a particular purpose. Creation of the vehicle has required mental effort to establish the specifications for the vehicle, and from there to provide details of the various features which are needed to make it work as efficiently as possible.
- In many cases the part played in the creation of a new man-made item can be too easily forgotten. But a good reminder can occur in a pharmaceutical pill, trifling in size but prodigious in price. A very small proportion is in the material - the main cost is for the immense human effort in creating the product, at the current average of US$1 billion per item.
Why should it be thought that no mental effort has been expended in the creation of living things, such as the seal? The eye of a seal is equally well adapted for seeing both underwater and in air. The cornea, the transparent circular outer covering at the front of the eye, has a flattened centre where refraction of light is nearly equal in both water and air.
- Seals also have a highly specialized irus - the coloured membrane with an opening in its centre (the pupil) which varies to control the amount of light reaching the retina (the light sensitive area at the back of the eye). The iris in seals is associated with much more muscle tissue and a greater density of blood vessels than in most other animals.
The unusually strong muscle in seals, which controls the size of the pupil, provides a very large range in the amount of light reaching the back of the eye. This is particularly the case in elephant seals which move from sunny beaches to near darkness during their deep dives.
- The tissue on the outer surface of the cornea includes keratin, a group of strong, fibrous proteins which are also the main ingredient in feathers, claws, hair and horns. This provides increased protection for the eye, while the extra thickness of the tough white outer layer of the eyeball, which is continuous with the cornea, adds sufficient strength to prevent implosion of the eye during deep dives.
Harp seals, with other seals which live in the bright and snowy environments of the polar ice, have corneas that are designed to better endure the high levels of ultraviolet radiation without ill effects, and so do not experience snow blindness.
- And so from the specialization of the eyes alone it is clear that this animal has been consciously designed for the function which it performs. More next time, God willing.