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What makes a rhinoceros look like a rhinoceros, or a petunia like a petunia? Understanding the basis of the generation of the forms, patterns, or shapes of complex organisms is a principal subject of biologist Gerald Edelman's stimulating book Topobiology, which explores the links among the development, evolution, form, and function of organisms.

In older scientific language, one could say that Edelman has brought a new dimension to morphology, the study of the form and shape of animate and plants, and to histology, the study of the minute structure of tissues. The major thrust of his book te what he calls a morphoregulatory hypothesis, which can be described as the outline of a molecular basis for the formation of pattern, involving three types of genes. In the morphoregulatory sequence, morphoregulatory genes control the production of molecules that cause the formation of clusters of cells. When the cell dusters begin to communicate, they activate another type (selector genes) that then select and switch on a third type of gene (historegulatory genes).

In the organisms they have studied, Edelman and his colleagues have found cell adhesion molecules (resulting from morphoregulatory gene action) that are attached to the surface of different cells and link them in clusters. These molecules can appear at different times in the development of a multicellular system, and at various specific sites on the cells. Furthermore, their chemical structure can vary. This tremendous variation allows a great flexibility in the kinds of linkages the molecules effect.

A second class of adhesion molecules plays a comparable role In attaching cells to the developing scaffolding of filaments that lie outside cells. Also of particular interest to researchers are what are called cell Junction molecules, composed of clusters of proteins providing small channels from the inside of one cell to the Inside of another. These three types of molecules facilitate a kind of conversation among eels that determines the course of development of organisms. It has been possible to demonstrate how Important these molecules are by treating tissues with agents that block their functions, thus effectively and drastically changing the organism's development.

Light exists on a spectrum of frequencies extending from gamma rays at the highest frequencies to radio waves at the lowest, though human eyes are sensitive to only a narrow range of frequencies in the middle known as the visible spectrum. The different colors we see correspond to the different frequencies of light within that range. Given that there are so many frequencies of light, one might wonder why our eyes didnt evolve to be sensitive to more frequencies.

Gamma rays from space collide with Earth's atmosphere, which converts some of their energy to heat and creates a distinctive cascade of subatomic particles down toward the ground. However, the rays themselves are entirety absorbed before they can reach Earth's surface. Thus, Earth would appear to be pitch black to eyes that were only sensitive to gamma rays. Similarly, the majority of frequencies of light that are higher or lower than those in the visible spectrum—such as ultraviolet and most infrared frequencies, respectively—are mostly or entirely absorbed by Earth's atmosphere.

One reason we see the frequencies we do is that visible-spectrum light generally passes through our atmosphere without being absorbed or reflected. Another reason is that the Sun, in some respects an average star, emits most of its light at frequencies in the visible spectrum, whereas a hot star emits most of Its light at ultraviolet frequencies and a very cool star emits most of its light at infrared frequencies. Indeed, to remarkably high precision, the human eye to most sensitive to the exact frequency in the yellow part of the spectrum at which the Sun is the brightest

Even if there are living beings on other planets, it is not likely that they would see mainly at very different frequencies than we do. Virtually all gases that are abundant in the cosmos tend to allow frequencies in the visible spectrum to pass through while absorbing other frequencies, and all but the coolest stars put out much, If not most, of their light in the visible spectrum. If there are Irving beings on other planets, they probably see at roughly the same frequencies as we do, though there may be occasional exceptions.

Consider a mirage on a hot toad: when light tays hit the hot ait just above the surface, they bend. Although light moves through a vacuum at a certain constant speed, it moves more slowly through any transparent medium, such as water or gas. Light travels faster in the thin air near the road than it does in the colder, denser air above, and the difference in speed makes it shift direction as it crosses the boundary between the two. Rays once headed downwards from the sky are redirected to your eye, hiding part of the road with a shimmering image.

A research team has constructed an apparatus to cloak an object from electromagnetic radiation (EMR)—in this case, microwaves—making the object "invisible" to microwave-based detection devices, somewhat as a mirage on a hot road makes the road invisible. The apparatus bends incoming microwaves around the object, using a class of recently created metamaterials—materials that gain certain desired properties directly from their engineered structures rather than from their composition. These metamaterials possess the ability, not found in nature, to bend microwaves at extreme angles. The metamateria! in this case—thin, rigid sheets of fiberglass insulator stamped with conducting loops, coils, and tiny rectangles—was designed to control the movement of incoming EMR.

Consider a mirage on a hot toad: when light rays hit the hot air just above the surface, they bend. Although light moves through a vacuum at a certain constant speed, it moves more slowly through any transparent medium, such as water or gas. Light travels faster in the thin air near the road than it does in the colder, denser air above, and the difference in speed makes it shift direction as it crosses the boundary between the two. Rays once headed downwards from the sky are redirected to your eye, hiding part of the road with a shimmering image.

A research team has constructed an apparatus to cloak an object from electromagnetic radiation (EMR)—in this case, microwaves—making the object "invisible" to microwave-based detection devices, somewhat as a mirage on a hot road makes the road invisible. The apparatus bends incoming microwaves around the object, using a class of recently created metamaterials—materials that gain certain desired properties directly from their engineered structures rather than from their composition. These metamaterials possess the ability, not found in nature, to bend microwaves at extreme angles. The metamaterial in this case—thin, rigid sheets of fiberglass insulator stamped with conducting loops, coils, and tiny rectangles—was designed to control the movement of incoming EMR.