Adaptability—the capacity to manage change is an invaluable trait in today’s ever-changing work environment. Adaptable workers are resilient, curious, and resourceful. They are willing to experiment and to risk failure. Most importantly, they understand the big picture, always keeping it at the forefront of everything they do. Some people are innately adaptable; others aren’t. Still, those who aren’t adaptable by nature can develop the qualities that help them to thrive on the job.
Adaptability is also a valuable quality in biology. In fact, many biologists believe that adaptability is one of the universally descriptive features of life. Organisms are exquisitely suited for their environments. Yet the environment changes. And like adaptable employees who can navigate workplace changes, organisms have the means to adapt to a shifting landscape. Those organisms that respond to change will persist; those that can’t will disappear.
Biologists have discovered a variety of mechanisms that operate at a population level that enable species to adapt to: (1) changes in the environment, (2) predatory pressure, and (3) fluctuating resources. The mechanism list includes: (1) natural selection, (2) sexual selection, and (3) genetic drift.
Recently, a large team of collaborators, headed by researchers from the University of California, Santa Cruz, highlighted another mechanism that they think contributes to organisms’ ability to adapt: introgression—the introduction of genetic material into the gene pool of another species through interbreeding or hybridization.1 Insights like this one are often viewed as prima facia evidence for life’s evolutionary history. But this discovery can also be viewed legitimately from a creation model standpoint, where adaptability reflects God’s providential care for his creation. In other words, God has designed the world so that populations of organisms have the innate capacity to adapt and ensure that they will survive and thrive.
Polar Bear and Brown Bear Introgression More evidence for the connection between introgression and adaptability became available when the UC Santa Cruz-led team examined the genome of a polar bear fossil specimen that age-dates between 70 and 110 thousand years ago. This specimen consists of a jawbone recovered from the beach near the Beaufort Sea by Port McLeod in Arctic Alaska.
From the ancient DNA extracted from one of the polar bear’s fossilized teeth, the team reconstructed high-quality sequences for the nuclear and mitochondrial genomes. The sequence data indicates that this specimen was indeed a polar bear but its genetic fingerprint falls outside the genetic diversity range for extant polar bears.
Comparison of this ancient polar bear genome with the genomes of extant brown bears indicates that the population to which the polar bear belonged interbred with a group of brown bears, around 100,000 years ago. As it turns out, these ancient recipients of the polar bear genetic material became ancestral to all brown bears living today. In fact, about 10% of the contemporary brown bear genome comes from this ancient introgression.
This discovery isn’t the first time that researchers have detected interbreeding between polar and brown bear populations. Around 15,000 years ago, an introgression event introduced polar bear DNA into brown bear populations in Alaska, resulting in a 6 to 8% contribution. The local population of brown bears found in Ireland harbors about 20% polar bear genetic material in their genomes, thanks to hybridization. However, these hybridizations only impacted local brown bear populations.
The most recently discovered hybridization event impacted all living brown bear populations (again, because it took place in a population of brown bears that gave rise to all brown bear groups extant today). Apart from having this newly sequenced paleogenome, researchers would not have known that this hybridization event took place. Instead, they merely assumed that the newly recognized polar bear contribution in current-day brown bear genomes was endemic to brown bears.
Interestingly, life scientists have only observed the flow of genetic material in a single direction during polar and brown bear hybridization: from polar bears to brown bears. The difference between lifestyles of these two bear species provides a way to rationalize this observation. Brown bears occupy a wide range of environments and consume a variety of foodstuffs. In fact, the biogeographical distribution of brown bears is one of the most expansive of any mammal species. On the other hand, polar bears live under a highly specific set of conditions among the arctic sea ice and consume a diet limited to other arctic sea mammals.
I suspect that the diverse lifestyle of brown bears makes their gene pool much more receptive to the introgression of new genetic information than the polar bear gene pool. The specialized nature of the polar bear lifestyle makes their gene pool much more resistant to the introduction of new genetic material, which, if it occurred, would, in principle, reduce the fitness of the polar bear population because they’re already exquisitely adapted to their surroundings.
The researchers note that this recently discovered hybridization took place at a time of climatic instability due to warming of the earth, resulting in rising sea levels. These changing conditions likely forced the geographical ranges for polar and brown bear populations to overlap, creating opportunities for introgression.
Under these changing conditions, the introgression of polar bear genetic material into the brown bear gene pool likely offered a fitness advantage for brown bears as they encroached on polar bear territories. In other words, the introduction of genetic material through introgression helped brown bears to adapt to a new environment.
Introgression and Adaptation One of Charles Darwin’s most important scientific accomplishments was to identify a mechanism to account for the origin of species. In the process, he demonstrated that species aren’t fixed entities but can change through natural and sexual selection.
These two mechanisms, along with genetic drift, allow populations of organisms to adapt. This adaptation can occur in one of two ways: (1) through changes in standing genetic variation in the population with the frequency of the alleles in the population changing in the response to environmental changes, or (2) through mutations that introduce new alleles altogether. The former mechanism leads to rapid response to environmental changes; the latter mechanism requires much more time to effect change.
Based on the recent work by the UC Santa Cruz-led investigators (along with other studies), introgression can be added to the list of mechanisms that serve as drivers for adaptive change.2 Adaptive introgression can rapidly introduce a large amount of new genetic information into a population across multiple genetic loci. The result is a response to environmental changes that’s more rapid than mutations afford and a more comprehensive response to environmental changes than is offered by changes in the frequency of already existing alleles.
Given that we appear to be in the early stages of significant worldwide climate change, adaptive introgression may become an even more important driver of adaptation, allowing organisms to not only survive but even thrive in a rapidly changing world. As climate change intensifies, it will undoubtedly alter the habitat range for many species—bringing populations of closely related species into close contact with one another and creating opportunities for introgression to take place. As a result, species populations that lack the innate genetic information to adapt to a rapidly changing climate can get a boost by the introgression of the genetic material of closely related species that are inherently suited to the emerging environmental conditions—in the same way that an employee not innately inclined to be adaptable can learn skills to manage change in the workplace.
Research team member Beth Shapiro states, “We shouldn’t be surprised to see admixture happening again today as the climate changes and these species are overlapping and encountering each other again in the wild . . . Climate change allows gene flow to occur between what we think of as different species.”3
Evolutionary Adaptation and God’s Providence From a creation model perspective, the adaptability of organisms is understood as part of the design God ordained in the biological realm. In line with Christian theology, the RTB model maintains that God not only created the world, but he also actively and continually preserves and governs all that he has made. God’s governance of the creation includes the natural processes he instituted when he brought the universe into existence. It is through these processes that he sustains the universe and everything in it.
For Christians, given what life scientists have learned about how these mechanisms provide the means for organisms to adapt to their surroundings, it makes sense to include evolutionary processes in the list of the natural processes that God providentially uses to sustain life on Earth.
Evolutionary Adaptation Is Not Evidence for the Evolutionary Paradigm On the other hand, just because one embraces organisms’ ability to adapt through evolutionary processes, it doesn’t mean they are obligated to accept the totality of the evolutionary paradigm. I don’t.
While abundant evidence exists for microevolution and adaptation (driven by natural and sexual selection, genetic drift, and, now, introgression), it isn’t clear that merely extrapolating these mechanisms over vast time periods can explain large-scale evolutionary change (macroevolution). To put it another way, it isn’t clear if natural and sexual selection, genetic drift, and even adaptive introgression can account for biological novelty and innovation—particularly when life transitions from one regime of complexity to another.
Biologists Doug Erwin and James Valentine make this point (with respect to the origin of body plans). They write, “One important concern has been whether the microevolutionary patterns commonly studied in modern organisms by evolutionary biologists are sufficient to understand and explain the events of the Cambrian or whether evolutionary theory needs to be expanded to include a more diverse set of macroevolutionary processes. We strongly hold to the latter position . . . The move from micro to macro forms a discontinuity.”4
These concerns have prompted some biologists to call for an extended evolutionary synthesis, acknowledging that current evolutionary theory is incomplete.5 While these calls don’t necessarily invalidate the evolutionary paradigm (which some creationists and ID proponents claim), they do mean that we currently don’t have valid mechanistic explanations for macroevolution and the origin of biological innovation and novelty.
These issues also mean that life scientists cannot legitimately enlist the sound and well-evidenced explanations for microevolution and adaptation in support of macroevolution. They also justify the skepticism that some ID proponents and creationists express about the capacity of evolutionary mechanisms to fully account for the origin, design, and history of life.
I wonder if modern-day biology will be adaptable enough to make a place at the table for ID and creation models—particularly in the face of the shortcomings of current evolutionary theory.
Ming-Shan Wang et al. “A Polar Bear Paleogenome Reveals Extensive Ancient Gene Flow from Polar Bears into Brown Bears,” Nature Ecology and Evolution 6 (June 16, 2022): 936–944, doi:10.1038/s41559-022-01753-8.
For example, see Philip W. Hedrick, “Adaptive Introgression in Animals: Examples and Comparison to New Mutation and Standing Variation as a Source of Adaptive Variation,” Molecular Ecology 22, no. 18 (September 2013): 4606–4618, doi:10.1111/mec.12415.
Paleontologists observe multiple “transitional forms” for whales in the fossil record. At first glance this evidence seems like a point in favor of the...
