In this series so far, we have explored what is known about the ultimate origins of biological information. Although, we know little about this subject, the facts we do know point to the genetic code—the mechanical basis for encoding and transmitting biological information—as having an origin shaped by chemical interactions. Accordingly, we have seen how these findings undermine the Intelligent Design (ID) argument that the genetic code was designed apart from a natural process.
A second claim commonly found in the ID literature is that—aside from the ultimate origins of biological information—evolution is unable to generate new information, or at least enough new information to produce the variety of life we observe in the present day. Claims of this nature are also commonly encountered in young-earth creationist (YEC) and old-earth creationist (OEC) circles. Given the prevalence of this claim in anti-evolutionary arguments, ID or otherwise, it’s worth delving into the evidence that evolutionary mechanisms do indeed have the ability to generate adequate amounts of new information to drive significant change over time.
Rarely is information truly “new”, and a little change goes a long way
Before discussing the known mechanisms that can produce new information, it may be helpful to provide some context. Two main points are important here: first, “new” biological information is seldom truly new. Secondly, biologists have good evidence that small amounts of new biological information are adequate to accomplish significant evolutionary change. Let’s examine these issues in turn.
Firstly, evolution is a process of descent with modification. This means that evolutionary change is not about producing “new” or “novel” forms, but rather slightly modifying existing forms. Allowing this process to unfold over millions of years can lead to significant change, to be sure—but from generation to generation within that process, the change is small. One excellent analogy for the gradual changes produced by evolution stacking up over time to accumulate major differences is that of language evolution—an analogy I have explored at length before. While Anglo-Saxon of the 10th century and present-day modern English cannot reasonably be called the “same language”, the process that produced the latter from the former was gradual enough that each generation spoke the “same language” as their parents and their children. So too with evolution—“new information” accumulates over time, usually by modifying what was there before. Even so-called “major innovations” in evolution are accomplished gradually—vertebrates are modified descendants of invertebrates; land animals are modified descendants of fish; whales are modified descendants of land animals, and so on. As such, it’s not reasonable to expect that rapid acquisition of large amounts of new information is needed to drive significant evolutionary change over time. Gradual accumulation will do.
Secondly, even a small accumulation of new information is enough to cause major evolutionary changes. One thing that we now know in this era of DNA sequencing is that species that are quite different from each other can nonetheless have very, very similar information content. A prime example is comparing human DNA with that of our closest living relatives, the other great apes. Human genes and chimpanzee genes, for example, are exceedingly close to one another in their information content and structure. We have only subtle differences at the gene level, by whatever measure one chooses—our genes (which are a small subset of our entire genomes, but the vast majority of the information that makes us up) are around 99% identical to each other. Yet these subtle information differences add up to quite significant biological differences. Many of the information differences between us are due to where and when our genes are active during development—subtle tweaks that ultimately lead to the marked differences we see between our species.
One of the ironies of Christian anti-evolutionary apologetics is that it is common to see groups argue both that humans and apes are hugely different from one another, and that evolution cannot produce significant amounts of new information. Well, one cannot have it both ways, now that we know that humans and other apes are so similar at the genetic level. If humans and apes are really that biologically different—and we are, to be sure!—then one is faced with the brute fact that these major biological differences are underwritten by a level of information change that is easily accessible to evolutionary mechanisms.
With these points in mind, let’s turn to discussing how DNA can change over time to produce new information.
Something old, something new
Darwin’s great insight about evolution was not that species shared common ancestors, but rather that species could be shaped, over time, by their environment to become better suited to it. Nature, he reasoned, could act in the same selective way that humans did to shape a species to a particular form. If populations have variation, and those variants do not reproduce at the same frequency in a given environment, then over time those variants best suited for that environment will increase in frequency, while those less suited will decrease in frequency. In this way, the average characteristics of a population could shift over time.
While Darwin understood these principles, he did not have any idea how variation was generated, or even how hereditary information was transmitted from one generation to the next. The discovery of DNA as the hereditary molecule provided the answers: DNA, in that it is faithfully copied from generation to generation, transmits hereditary information. In rare cases where DNA copying is not perfect, then new variation enters the population. DNA replication then, is both the means of maintaining information and introducing change.
While DNA is great at storing and transmitting information, it is lousy at performing the day-to-day biological functions that cells need to do—enzymatic functions, energy processing functions, and so on. These functions are performed by proteins, which are lousy molecules for storing information, but fantastic molecules for getting biological work done. RNA, as we have seen, is the bridge between these two worlds—a gene, made of DNA, is transcribed into a working copy of RNA called a messenger RNA (mRNA), which is then translated by the ribosome into a protein. The information in a gene—a DNA region—can thus be used to specify how a protein is shaped, and where and when it is made during an organism’s development. The gene regions that specify the protein structure are called coding sequence, and the DNA that specifies where, when, and how often a gene should be transcribed (and translated) are called regulatory DNA. For a given gene, some regulatory DNA is outside of the transcribed region, and some is within it. Biologists often talk about genes being “expressed” as a shorthand for a gene being transcribed into mRNA and translated into a protein. Regulatory DNA, then controls the “pattern of expression” for a gene.
As we can now appreciate, there are several ways for the information content of a gene to change. There could be a DNA sequence change (a mutation) in any part of a gene’s DNA sequence. If a change occurs in the coding sequence, there may be a change in the protein sequence—one altered amino acid, for example—perhaps giving rise to a change in function. If a change occurs in regulatory DNA, then the new variant might have one or more of several possible changes: either an increase or decrease in the amount of RNA that is transcribed, the gene being newly transcribed at times or places it was not transcribed before, or the loss of transcription at times or places where it previously was expressed.
More dramatic changes in information state are also possible. Deletion mutations can remove a gene in its entirety; or a duplication mutation could produce two copies of a gene, side by side. An interesting effect of duplication mutations is that the two copies sometimes go on to accumulate differences (in their amino acid sequences or in their regulatory DNA, or both) that lead to them acquiring distinct functions. In this way, new functions may develop over time. There are even cases known when entire chromosome sets of an organism were duplicated at once—a so-called “whole genome duplication” or “WGD” event. For example, there is very good evidence that early vertebrates had two WGD events in their lineage—the effects of which can be seen in all vertebrates living today, including humans. While many of the duplicated genes have been lost, others were retained and, over time, picked up sequence changes and functional changes. This greatly added to the information content of the vertebrate lineage.
One possible twist on the “WGD” theme is the case of hybridization—when two related but distinct species interbreed and form fertile progeny. In this case, two species diverge from a common ancestor, and over time, differences in their genes accumulate. This is also a form of information gain over time, except the gain is distributed between two related species/populations. If these two species later interbreed to form a hybrid, then the offspring will inherit one chromosome set from each species.
This situation may not be ideal, if a significant amount of change has accumulated between the two species. It may be the case that the chromosomes from each species may not readily pair with their “equivalent” chromosomes from the other species for the purposes of cell division. If so, then a WGD event may provide a fix to the less than ideal situation—a WGD event occurring after a new hybrid species forms duplicates every chromosome in the genome—giving each chromosome a new, perfectly matched partner to pair with. The end result is a species that has fully two genomes within it—a full genome from each pre-hybridization species. Moreover, the two genomes are already slightly different from one another, meaning that they are already down the path of picking up slightly different functions.
From this starting point, further changes over time are probable—shifting the information state of both ancestral genomes within the “doubled hybrid” species. A recent scientific paper provides an excellent illustration of exactly this process—the discovery that the frog species Xenopus laevis has two complete genomes from two (now extinct) ancestral species—species that were separate from one another for several million years before hybridizing.
Human genome sequence data has also revealed, in recent years, that the lineage leading to modern humans also hybridized with related hominin species in the past—species such as Neanderthals, the Denisovans, and likely others. While modern humans do not retain much of the DNA we picked up from these species, we do nonetheless retain some, and some of it is likely of functional significance for some human groups. We too have shifted our information state by this means.
It’s important to keep in mind that all of these changes in information state are based on well-known and understood mechanisms. We can observe these mechanisms occurring in the present day, and we know—from comparing the DNA of related species to each other—that a small amount of genetic change can bring about significant morphological change. As such, the claim that evolution is incapable of generating the new information needed to drive species change over time is not supported by the evidence, but rather is in stark contrast to it.
Still, one might say—these forms of information change over time merely modify existing information. Even if evolution can get a reasonable amount accomplished with modification, is it the case that evolution cannot create something truly new? As we will see in the next post in this series, evolutionary mechanisms—despite ID claims to the contrary—can and do produce genuinely new information as well.