The Evolving Peppered Moth Gains a Furry Counterpart

H. E. Hoekstra
Evolution has allowed some rock pocket mice,
pictured on light and dark rocks, to produce
distinct fur that helps disguise them.

In the deserts of the Southwest, among the towering saguaros and the spiny cholla cactuses, rock pocket mice hop and dash in search of a meal of seeds. But while these mice may seem to scamper haphazardly across the desert floor, their arrangement in nature is strikingly orderly.

Nearly everywhere these mice are sandy-colored, well camouflaged as they scurry across beige-colored outcrops. But in some areas, ancient lava flows have left behind swaths of blackened rock. There the same species of rock pocket mouse has only dark coats, having evolved an entirely distinct and, for their surroundings, equally well-disguised pelage.

Now, in a recent study in The Proceedings of the National Academy of Sciences, researchers report identifying the gene responsible for the evolution of dark coat coloration in these mice, pinpointing the DNA sequence changes that underlie this classic story of evolutionary change, the cute and furry counterpart to the famous case of the peppered moth.

Researchers say the study is the first documentation of the genetic changes underlying an adaptive change where the evolutionary forces were natural. Scientists point out that other well-known cases involve evolution caused by humans; some have suggested that those changes may be atypical of natural evolutionary change, since they have typically involved intense, directed pressures destroying most of a population, like the spraying of pesticides or the application of antibiotics.

"This work is very important," said Dr. Mike Majerus, an evolutionary geneticist at Cambridge University, who was not part of the study. "Here man is just not involved. The sandy and lava flow substrates are entirely natural phenomena."

Other well-studied examples of human-driven adaptive change include the evolution of pesticide resistance in insects after widespread spraying and the increase in the numbers of dark-winged forms compared with light-winged forms of the peppered moth in the United States and England after industrialization turned air sooty and polluted.

Dr. Michael W. Nachman, a population geneticist, along with colleagues at the University of Arizona, Dr. Hopi E. Hoekstra and Susan L. D'Agostino, studied mice living on Arizona's Pinacate lava flow in Arizona and on light-colored rocks nearby. The researchers were able to take advantage of decades of meticulous work in which other scientists identified some 80 genes that affected coat color in laboratory mice.

On close examination, the light-colored rock pocket mice could be seen to have a type of hair coloration similar to standard, sandy-colored laboratory mice. In this pattern, known as agouti, the hair is black at the base, yellow in the middle and black again at the tip. The dark-colored rock pocket mice had completely dark hairs.

Researchers knew that mutations in a few well-known coat coloration genes in laboratory mice could cause such complete darkening of the hair, and they began by looking at two genes known as agouti and Mc1r. When they looked at DNA sequences in light and dark mice, changes in the agouti gene did not appear to be associated with light-colored fur versus dark-colored. Still, the researchers found that a certain cluster of mutations at Mc1r could be found in every dark-colored mouse.

"It's a textbook story," Dr. Nachman said. "Now we have all the pieces of the puzzle together in a natural setting."

Dr. Nachman noted that while the new study points to the Mc1r gene as the key to turning mice dark on the Pinacate lava flow, the team also found that dark mice on another lava flow in New Mexico did not share those mutations.

"So the same dark color has evolved independently in the two different populations," he said, "through different genetic solutions to the same evolutionary problem." Dr. Nachman said changes in another gene, perhaps the agouti gene, could be responsible for dark coloration in the New Mexico's Pedro Armendaris lava flow.

One could easily imagine that coloration would be of no consequence to the rock pocket mice, as they are nocturnal, darting about under the desert night sky. But researchers, working early in the last century, released light and dark mice on light and dark backgrounds in an enclosure at night and found that owls, a major predator of mice, could easily spot a mouse on a mismatched background.

Dr. Nachman noted, however, that these early researchers did not use rock pocket mice in their study, but instead used a species in which the dark and light forms were actually much less distinct.

As a result, he said, "we think the owls are discriminating even more strongly in our species." He said tiny bits of rock pocket mouse were often found in pellets at owl roosts.

Dr. Majerus said many kinds of animals showed light and dark forms, from deer mice to squirrels and chipmunks. There are even black ladybugs.

"A lot of the dark forms show an association with a particular type of substrate they're on, or the frequency of burning and charring of the trees in the woodlands," he said, noting that it would be interesting to do genetic studies in other animals, to see how many genetic solutions these other animals have come up with to turn dark.

But while many dark forms are abundant and can be studied at scientists' leisure, Dr. Majerus said that of the peppered moth was slowly disappearing.

So while there is nearly unanimous praise for the increasingly clean air in industrialized regions of the United States and Britain, there may be, at least for some scientists, a downside. "We've got about 15 or 16 years," Dr. Majerus said, "before those black forms, if they continue to disappear at the current rate, disappear completely."

ABIOGENESIS

That slow process by which living organisms were spontaneously generated from non-living matter. This scientific fact should not be confused with the old discredited myth of spontaneous generation by which it was once foolishly believed that living organisms arose from non-living matter. (see Law of Biogenesis).

A.C.L.U.

An organization that zealously protects our American civil liberties by preventing students in public schools from considering scientific evidence that is either consistent with creation or critical of evolution.

BIG BANG

The mechanism, or at least the noise, by which all matter and energy came into existence billions of years ago.

BIOLOGY

The branch of the exact sciences which is exclusively concerned with the evolution of living organisms by means of random mutations and natural selection.

DROSOPHILA

The "guinea pig" of the evolutionist to which we all owe a debt of gratitude for our understanding of the role of mutations in evolution. Trillions of generations of these rapidly breeding little flies have had their wings crumpled and their eyes damaged by strong mutagenic agents to provide us with a genetic insight into how man evolved from the prehominid brutes in a few thousand generations.

EVOLUTION

A truly perfect scientific theory which explaims in detail how everything in the universe came into being -- slowly. The theory of evolutions is so perfect and flexible in its ability to explain virtually all observable phemomena or opinions that it would be impossible to even conceive of an experiment capable of disproving it. (see Law).

GEOLOGIC COLUMN

A precise hierarchy of fossilized animals and plants of known age found in successive layers of stratified rock with the simplest and oldest at the bottom and the most highly evolved, i.e., most recent, at the top. Uninterrupted columns of this type may be found in any book of geology, paleontology or evolution. Bits and pieces of the column may even be found in the stratified rocks of the earth, but since these layers are often out of correct order and very incomplete, one should study the geologic column in books, not nature.

HOPEFUL MONSTER THEORY

A concept first introduced out of necessity by the geneticist, Richard Goldschmidt, which states that evolution occurs by sudden and large changes in the offspring of a species resulting in radically different but well adapted organisms, i.e. "hopeful monsters." After being widely discredited for many years this idea is being reintroduced, out of necessity, as a serious theory. The great leaps forward implicit in this theory entirely account for the absence of the "missing links." (See Punctuated Equilibrium)

INDEX FOSSILS

Fossils of animals whose ages are precisely known from the age of the rocks in which they are found, thus, serving as a means for accurately dating the rocks in which they are found as well as the age of any other fossils that may be contained therein.

LAW

In science, a statement of fact about a sequence or phenomenon that has been invariably observed to occur under known conditions such as, for example, the theory of evolution. (see Evolution).

LAW OF BIOGENESIS

Simply states the obvious...that all life comes from pre-existing life. This law, which was confirmed by Redi and Pasteur, permanently laid to rest the ludicrous idea of the ignorant ancients that living organisms could spring from inanimate matter. It should be emphasized that this law in no way precludes the slow origin of living organisms from inanimate matter through the process of evolution - after all, we are here, aren't we? (see Abiogenesis).

LIFE

The only term in this dictionary that defies definition since it has been said that "the division of matter into living and nonliving is perhaps an arbitrary one. It is a convenient method for distinguishing, for instance, a man from a rock." (quoted verbatim from The Origins of Life, by Cyril Ponnamperuma, 1962, H. P. Dutton, New York, p. 36).

MICROSPHERES

Primitive cells which have been artificially synthesized from simple laboratory reagents. As the name implies, the principal similarity between microspheres and living cells is that both are small and sort of round.

MISSING LINKS

An inconceivably vast assemblage of plants and animals which are intermediate in their evolutionary development between all of the discrete kinds of plants and animals one sees either alive or in the fossil record. Unfortunately as the name implies they are missing.

MUTATIONS

A change in the genetic material (DNA) of the cell induced by hazardous chemicals or radiation which in addition to killing or maiming organisms will, given enough time and enough mutations, inexorably lead some organisms on to an ever more successful and adaptive life.

NATURAL SELECTION

That miraculous process by which incredibly complex and useful structures, such as the eye or brain, are culled out from a vast array of random and purposeless mutations. In the distant past this marvelous natural artificer has produced the whole scope of existence from molecules to man but today it appears to be limiting its activities to such mundane matters as controlling the relative numbers of white and black moths in England.

NEO-DARWINIAN EVOLUTION

An embellishment of the old Darwinian theory of evolution, it states that random changes (mutations) in the genome of an organism will be selected for, and thus contribute to the evolution of the new species, only if they ultimately lead to a greater number of offspring. Thus, an ever-increasing rate of reproduction entirely accounts for the evolution from bacteria to man.

ONTOGENY RECAPITULATES PHYLOGENY

A law first discovered by Ernst Haeckel which if pronounced correctly and with conviction, impresses laymen and students of science in the elementary grades. Simply stated, and thus less convincingly, it means that the embryos of all animals bother to provide a historical review of many stages of their evolution during their embryological development. Although this type of reminiscing is touching and is taught in almost every general science and biology text book, it is no longer accepted by scientists or even evolutionists.

PHYLOGENETIC TREE

A tree that grows mainly in textbooks of biology and which has a variety of both contemporary and fossil animals perched on the tips of its branches. This tree clearly shows how all of these animals branched off from common ancestors a long time ago. For some reason the common ancestors are never shown sitting in the crotches of the tree. Plants presumably grow on different trees which are rather rare.

PILTDOWN MAN

Once known by all true scholars of human evolution to be an ancient ancestor of man. This true "ape man" had the jaw of a modern ape and the skull of a modern man. Today this ape-man is not so well known among true scholars of evolution.

PRIMITIVE

Old, inferior, poorly adapted, less evolved, shoddy, bungling.

PROOF

The assimilation of data in such a way that the desired conclusion seems to be the most plausible hypothesis.

PROTOZOA

As the name implies, these are known to be the first true animals on earth. If these primitive organisms had continued to adapt to their changing environment they might still be with us today.

PUNCTUATED EQUILIBRIUM

An ad hoc hypothesis or alibi that claims the reason there are no known transitional forms in the fossil record is because evolutionary changes occur so quickly and the reason we can't see evolutionary changes in the laboratory is because they occur so slowly. (see Hopeful Monster Theory).

RADIOCARBON DATING

A remarkably precise method of actually measuring the age of any carbon-containing sample. Except for certain spurious (young) dates, radiocarbon, like other methods involving the decay of radionuclides will, given several absolutely safe assumptions, invariably indicate a ripe old age for any specimen consistent with a slow process of evolution.

SECOND LAW OF THERMODYNAMICS

One of the most fundamental laws of science which essentially states that nothing can increase in order, complexity, or information but rather everything form the universe to the one-horse shay will in time fall apart (not assemble). We may be sure, however, that the mind-boggling increase in order, complexity and information accomplished by the evolution of chemicals to man in no way violates this law or it wouldn't have happened.

SELECTIVE PRESSURE

That natural and highly selective pressure that actually forces particularly useful structures such as brains, eyes, legs, wings and long necks on giraffes to evolve by random mutations. Unnecessary structures such as eyelids on your navel fail to evolve by chance because there is no selective pressure for this.

SPECULATION

The single most powerful tool in the hands of the evolutionists.

SURVIVAL OF THE FITTEST

The most important contribution of Darwin to biological thought which states that only those organisms which are fit survive, or in other words, survival is the result of being fit. By this kind of logic it can also be proven that loss of vision is a principal cause of blindness.

THEISTIC EVOLUTION

The belief that the evolutionary account of origins (where everything ascends from a very imperfect state to a more nearly perfect state) and the Biblical account of origins (where everything descends from a perfect state to a very imperfect state) are both true.

TIME

That miracle ingredient which in sufficient quantity can give scientific credibility to any hypothesis no matter how improbable. It is a well- known axiom of science for example, that given enough time virtually anything is possible - indeed you might even say it has to happen.

TREE

That which only evolution can make. (see Phylogenetic Tree).

VESTIGIAL ORGANS

Organs or other body parts, left over from evolutionary ancestors, which are no longer used or needed by an organism that has become more highly evolved by abandoning organs and getting simpler. Seventy years ago man had nearly one hundred vestigial organs such as the parathyroid, tonsils, coccyx, etc., but today he has very few vestigial organs because a good use has been discovered for most of these organs.

XERDEMA PIGMENTOSA

A disease of man in which certain enzymes which normally repair mutations of DNA fail to do so resulting in malignant tumors of the skin which are often fatal. Since it is well known that mutations were essential for the evolution of man from primitive cells, we must assume that too much of even a good thing like mutations is bad for us.

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