An interesting development is taking place in the biological and anthropological sciences today that has its roots in a decades-old discussion. Whispers in the halls of scientific faculties and hushed conversations in laboratories have solidified into outright dialogue and debate in top scientific journals. Scientists from across the various evolutionary disciplines have locked horns over the accepted mechanisms of standard evolutionary theory (SET) and the significance that ought to be afforded to each mechanism. Let me be clear upfront, the core of Darwinian evolution itself is NOT being questioned. Indeed, as Dobzhansky, echoing Teilhard de Chardin, asserted decades ago, “nothing in biology makes sense except in the light of evolution.” It is uncontested that variation occurs in populations and is subsequently winnowed by natural selection, generating biological change over time. SET contends biological diversity is mostly explained by natural selection, defined as the confluence of random phenotypic variation, genetic inheritance, and differential reproductive success. However, some scientists (proponents of the “extended evolutionary synthesis,” or EES) are challenging the tenet that phenotypic variation is entirely random and that natural selection is entirely driven by genetic inheritance. The dialogue focuses on the processes within evolution, where to put causal emphases, and sometimes just what to call things. These scientists are working to hone our understanding of evolutionary theory at present—even if they disagree on the severity of this honing process. The controversy helps highlight the sheer breadth and intricacy of modern evolutionary theory, which cuts across many interdisciplinary lines.
The topic of these conversations even made their way into our recent symposium on Christian doctrine and evolutionary theory. It came up when our team was deciding what kind of evolutionary scientists it would be important to invite to the symposium. Should we invite mostly evolutionary biologists? Geneticists? Paleontologists? Even psychologists and culture experts? Evolutionary theory plays a significant role for so many scientists today. A complete picture of evolutionary theory would not be possible without referencing how it functions in each of these areas, yet scientists are divided on how to parse out the significance attributed to each of these areas.
A recent article in Nature elucidates well the growing momentum of this conversation, as seen by its provocative title: “Does Evolutionary Theory Need a Rethink?” In the article, two teams of scientists respond to this question. Kevin Laland and colleagues think evolutionary theory does need to be reassessed, while Gregory A. Wray, Hopi E. Hoekstra, and colleagues agree evolutionary theory is fine as it is.
Laland et al. argue that new scientific developments in genomics, epigenetics, developmental biology, social science, and ecology are altering the prevailing, gene-centric view of evolution. They contend that organisms are not simply genetically programmed from birth to fit into a prior environment but instead can “co-construct and co-evolve with their environments, in the process changing the structure of ecosystems.” in EES.
Laland et al. explain that phenotypic plasticity is also changing the gene-centered view of evolution. Phenotypic plasticity refers to the way certain organisms can directly alter their morphology, physiology, and behavior in response to an environmental change. What is interesting about these changes is that they occur within the lifetime of the individual organism itself rather than lagging behind in evolutionary time. While plasticity is most drastic with static organisms such as plants (i.e., they cannot move away from their environment and have evolved to adapt directly to their changing environment), it is also visible with insects and animals. As an example, certain grasshoppers, such as Schistocerca gregaria, change from docile, solitary creatures to the well-known, aggressive locusts when surrounded by many others of the same species. They even change color to denote this change in behavior. Laland et al. suggest these immediate phenotypic changes can help prime the genetic pump by helping to select organisms that have the advantageous phenotypic trait—paving the way for the subsequent underlying genes. As Laland et al. says “often it is the trait that comes first; genes that cement it follow, sometimes several generations later.”epigenetic markers, but it can also include the transmission of social behavior (i.e., social learning and cultural evolution) and even ecological inheritance (e.g., a beaver passing down his dam to subsequent generations). Epigenetics is one of the most fascinating areas of extra-genetic inheritance and has received a lot of attention in recent years. Epigenetics is the field that looks at “the heritable changes in gene expression (active versus inactive genes) that does not involve changes to the underlying DNA sequence; a change in phenotype without a change in genotype.”can be transmitted to progeny up to two to three generations. This means that our actions today can directly influence the phenotype of our children and grandchildren through these epigenetic markers.
Now, those in the “No” camp (Wray, Hoekstra, and colleagues) agree each of these mechanisms play a role in evolutionary development; however, they contend SET already makes room for these mechanisms, and thus, evolution does not require redefinition. The central point of disagreement, then, is the significance these other mechanisms have to the theory of evolution. Laland et al. clearly want the genetic throne of evolutionary theory shared with other extra-genetic features. However, Wray, Hoekstra, and colleagues are hesitant to allow the genetic core to be dissolved and give equal value to extra-genetic mechanisms. They have two central concerns. First, there has not been enough experimental evidence as of yet to warrant changing SET. To do so would be too hasty. The second concerns the priority of the current genetic basis of evolutionary theory to these other extra-genetic mechanisms. At the heart of the article the naysayers pose a very important and illuminating question: Could these extra-genetic mechanisms “lead” evolution rather than merely fine-tune or hone the existing underlying genetic engine?
It seems to me this is an important question and will largely dictate whether the present theory needs significant overhauling. What would it mean to “lead” evolution? Clearly, Laland et al. would contend that evolution can be “led” by many of these extra-genetic mechanisms. For instance, phenotypic plasticity might help lead evolution by providing an immediate advantageous trait in a given environment, helping to select and funnel the underlying genetic code in a particular direction towards the advantageous trait expressed by phenotypic plasticity. This phenomenon has often been referred to as genetic assimilation, and it has a very under-represented scientific heritage.Laland K, et al. 2014. “Does Evolutionary Theory Need a Rethink?” Nature. 514, no. 7521: 162.[return to body text]
This is a companion discussion topic for the original entry at https://biologos.org/blog/the-changing-face-of-evolutionary-theory