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To determine what sorts of genetic changes macroevolution requires, one first needs to be clear on what key feature of biological organisms macroevolution must explain. A biological organism is more than the sum of its individual structures. In discussions of biological evolution, this point is often missed because evolution is thought to proceed by cumulating advantages. But organisms are not just bundles of accumulated advantages. An organism’s ability to function successfully requires an entire adaptational package, that is, a set of structures that are carefully coordinated with one another to help the organism make a living. The challenge for macroevolution is to bring about such adapational packages.
An excellent example of an adaptational package is the giraffe. What impresses people most about the giraffe is its long neck. Darwin himself drew attention to the giraffe’s neck. In the Origin of Species he wrote:
The giraffe, by its lofty stature, much elongated neck, forelegs, head and tongue, has its whole frame beautifully adapted for browsing on the higher branches of trees. It can thus obtain food beyond the reach of the other Ungulata or hoofed animals inhabiting the same country and this must be a great advantage to it….1
The advantage of the giraffe’s long neck for “browsing on the higher branches of trees” is, however, not nearly as obvious as Darwin makes out. Consider that the neck of the female giraffe is two feet shorter, on average, than that of the male. If a longer neck were needed solely to reach above the existing forage line, then the females would have soon starved to death and the giraffe would have become extinct.
Darwin was correct when he called the giraffe “beautifully adapted,” but he did not have enough information to appreciate the full extent and refinement of the adaptations. Observe some giraffes eating and drinking in the zoo and you will notice that they don’t just raise their heads to eat leaves high up in trees but also bend their heads to the ground to eat grass and drink water. Given their long legs, giraffes could be said to need a long neck less to reach up into the trees (which are not the only source of vegetation in many terrains) than to reach the ground to drink water.
The giraffe is an integrated adaptational package whose parts are carefully coordinated with one another. To fit successfully into its environmental niche, the giraffe presumably needed long legs. But in possessing long legs, it also needed a long neck. And to use its long neck, further adaptations were necessary. When a giraffe stands in its normal upright posture, the blood pressure in the neck arteries will be highest at the base of the neck and lowest in the head. The blood pressure generated by the heart must be extremely high to pump blood to the head. This, in turn, requires a very strong heart. But when the giraffe bends its head to the ground it encounters a potentially dangerous situation. By lowering its head between its front legs, it puts a great strain on the blood vessels of the neck and head. The blood pressure together with the weight of the blood in the neck could produce so much pressure in the head that, without safeguards, the blood vessels would burst.
Such safeguards, however, are in place. The giraffe’s adaptational package includes a coordinated system of blood pressure control. Pressure sensors along the neck’s arteries monitor the blood pressure and can signal activation of other mechanisms to counter any increase in pressure as the giraffe drinks or grazes. Contraction of the artery walls, the ability to shunt arterial blood flow bypassing the brain, and a web of small blood vessels between the arteries and the brain (the rete mirabile, or “marvelous net”) all control the blood pressure in the giraffe’s head. The giraffe’s adaptations do not occur in isolation but presuppose other adaptations that all must be carefully coordinated into a single, highly specialized organism.
In short, the giraffe represents not a mere collection of isolated traits but a package of interrelated traits. It exhibits a top-down design that integrates all its parts into a single functional system. How did such an adaptational package arise? According to neo-Darwinian theory, the giraffe evolved to its present form by the accumulation of individual, random genetic changes that were sifted and preserved piecemeal by natural selection. But how could such a piecemeal process, in which mutation and selection act on the spur of the moment with no view to the future benefit of the organism, bring about an adaptational package, especially when the parts that make up the package are useless, or even detrimental, until the whole package is in place? That’s the trouble with integrated packages — they are package deals that offer no benefit until the entire package is in place.
To be sure, random genetic changes might adequately explain changes in a relatively isolated trait, such as an organism’s color. But major changes, such as the evolution of a giraffe from an animal with short legs and short neck, would require an extensive suite of coordinated adaptations. The complex circulatory system of the giraffe must appear at the same time as its long neck or the animal will not survive. If the various elements of the circulatory system appear before the long neck, they are useless or even detrimental. This interdependence of structures strongly suggests a top-down design that is capable of anticipating the total engineering requirements of organisms like the giraffe.
The biological literature is filled with examples of adaptational packages. Some organisms, such as arthropods (a group that includes modern crabs and lobsters), even appeared with their adaptational packages intact during the Cambrian explosion. The Cambrian explosion marks the sudden appearance in the fossil record of numerous multicellular animals exhibiting diverse body plans. For most of these animals, evidence of fossil ancestors is completely lacking (with but one or two exceptions, there are no known Precambrian precursors). And yet these organisms arrive fully formed in the fossil record as integrated adaptational packages.
As always, microevolution is not the issue here. Moth populations that over generations shift in color from light to dark or mosquitoes that exhibit resistance to DDT are often cited as examples of evolution by natural selection. But such examples only illustrate small changes in the gene frequency of populations. A shift in the dominant moth coloring requires no new genetic information because the alleles (variant genes) are already present in the population. In contrast, major changes require major coordinated adaptations, which in turn require impressive amounts of new functional and genetic information. When we fully appreciate the informational requirements for the origin of even a modest new biological structure, much less the origin of a major adaptational package, we can see what a tall order it is for blind mechanisms such as mutation and natural selection to account for them.
According to E.J. Ambrose, selection pressure from the environment is too general for the demands of evolution: “The sort of message which the physical or biological environment can transmit to the organism in the way of new information is an extremely simple one, of the yes or no type such as ‘Can I find food higher up the hill or not?'”2 Simple information like this, however, even when cumulated over time, is not the tightly integrated information needed to coordinate the numerous changes that must occur to build novel complex biological structures and body types. To evolve novel adaptational packages, populations face an information hurdle.
One way to see this hurdle is in the phenomenon of phylogenetic inertia. Phylogenetic inertia denotes the tendency of populations to maintain an average morphology as well as a limited degree of variability around the population average. How can mutations overcome phylogenetic inertia to evolve new adaptational packages? It’s not clear that they can. Chromosome mutation may exchange parts of gene sequences. But there is no evidence that such “new” genes can provide the steady accumulation of novel traits (to say nothing of their coordination) that natural selection needs for Darwinian evolution to be effective. Chromosome mutation merely reshuffles existing genes.
The only known way to introduce genuinely new genetic information into the gene pool is by mutations that alter the nucleotide bases of individual genes. This is different from chromosome mutation, in which sections of DNA are duplicated, inverted, lost, or moved to another place in the DNA molecule. Point mutations do not merely rearrange but fundamentally alter the structure of existing genes. Such mutations typically result from random copying errors of DNA and are intensified through exposure to heat, chemicals, or radiation.
Could chromosome and point mutations working in tandem provide the raw material for macroevolutionary change? As the primary source of evolutionary novelty in the neo-Darwinian theory, mutations have been studied intensively for the past half-century. The fruit fly is a case in point. Its genome is easily manipulated and its short lifespan and reproductive cycle allows scientists to observe and track many generations. As a result, it has been the subject of numerous experiments. By bombarding it with radiation to increase the rate of mutations, scientists now have a pretty clear idea what kind of mutations can occur.
There is no evidence of mutations in fruit flies creating new structures. Mutations merely alter existing structures. For instance, mutations have produced crumpled, oversized, and undersized wings. They have produced double sets of wings (one set of which doesn’t work and thus is deleterious to the organism). But they have not created a new kind of wing. Mutations have also created monstrosities, like fruit flies with legs growing where they should have antennae (a condition known as Antennapedia). But even such monstrosities merely rearrange existing structures, albeit in bizarre ways. Nor have mutations transformed the fruit fly into a new kind of insect. Experiments have simply produced variations of fruit flies.
In conclusion, to generate an adaptational package requires not piecemeal change but integrated, systematic change. Moreover, the source of such change must impart massive amounts of new functional information into an organism. Such information, however, gives no evidence of resulting from the interplay of mutation and selection. Indeed, it gives no evidence of being reducible to matter and energy at all.
As Norbert Wiener, one of the founders of information theory, remarked: “Information is information, not matter or energy. No materialism which does not admit this can survive at the present day.”3 Just as the information on a book’s printed page is distinct from the ink and paper that make up the page, so the information in biological systems is distinct from its material constituents. What is the source of the information needed to build adaptational packages? As with the information in written messages and engineered systems, the only source known to be capable of generating information such as we see in biological systems is intelligence.
(2) E.J. Ambrose, Nature and Origin of the Biological World, 140-41.
(3) Norbert Wiener, Cybernetics: or Control and Communication in the Animal and the Machine, 2nd ed. (Cambridge, Mass.; MIT Press, 1961), 132.