Today’s New Reason To Believe

Ancient DNA Analysis Sheds Insight into the Micro-Evolutionary Origin of Lactase Persistence

It’s hard to imagine a refrigerator (at least in the U.S.) that doesn’t have a gallon or two of milk in it. Milk is a staple in the diet of humans—young and old—around the world.

But it wasn’t always that way. For much of human history, people lacked the ability to digest milk as adults. Humans suffered from this deficiency because they stopped producing the digestive enzyme for the milk sugar, lactose, as they grew out of infancy.

The enzyme lactase (which breaks down lactose) is produced in all mammals (including humans) at an early age. Normally, the gene for this enzyme is not expressed as mammals mature. In some human adults, however, the gene for lactase is expressed into adulthood. This condition, referred to as lactase persistence, appears to have evolved in humans when animal domestication became widespread about 10,000 years ago as part of the Neolithic revolution.

Lactase persistence is commonplace in Northern and Central European populations and occurs to a lesser extent in people groups from Southern and Eastern Europe. The ability to digest milk sugar into adulthood varies for Middle Eastern and African populations, correlating with pastoralist lifestyles. Interestingly, recent work indicates that lactase persistence evolved independently in European and African people groups.¹ In European people groups, lactase persistence stems from a single change (or mutation) in the part of the DNA sequence that controls expression of the gene that encodes lactase. A different mutation yielded lactase persistence in African populations.

Evolutionary biologists propose two models to explain the origin of lactase persistence. The lead hypothesis argues that the mutation that led to lactase persistence occurred recently after animal domestication took place. (Most studies support this idea.) The ability to digest nutrient-rich animal milk offered an obvious advantage and consequently took hold and spread quickly among human populations. The other model—a reverse-cause hypothesis—asserts that the mutation for lactase persistence was present in humans well before the Neolithic revolution. This model maintains that only those humans with the ability to digest lactose domesticated animals. Those who couldn’t didn’t pursue that particular lifestyle.

A recent study, which explored the natural history of lactase persistence, directly evaluated these two models.² Researchers analyzed ancient DNA isolated from the fossil remains of eight humans found in several sites in Europe for the DNA mutation that imparts lactase persistence. These human fossils dated between 7,000 and 8,000 years in age. The analysis revealed no evidence for lactase persistence in any of the human remains. There is no reason to believe that lactase persistence existed prior to the Neolithic revolution. It appears that humans recently evolved the ability to digest milk sugar in adulthood after animals were first domesticated.

Is evidence that humans evolved evidence for human evolution (the notion that humans emerged from an ape-like creature over the span of 6-7 million years through a series of transitional forms)? Not necessarily. (There are many reasons—see Who Was Adam?—to be skeptical of evolutionary explanations for the origin of humanity.) The emergence of lactase persistence is simply an example of a microevolutionary change—variation within a species—in which a single mutation, in this case, alters the expression of a single gene, allowing humans to persist in their ability to digest milk sugar into adulthood. In fact, it could be argued from a creationist perspective that the ability of humans (and other creatures) to adapt through microevolutionary change is evidence for God’s provision and providence.

The evolution of lactase persistence falls into the same category as: (1) the acquisition of antibiotic resistance by bacteria; (2) the development of pesticide and herbicide resistance by insects and plants, respectively; (3) the change in wing color of the peppered moth; and (4) the variation in beak shape by the finches on the Galapagos Islands. These common examples of evolutionary changes are often cited as evidence for biological evolution. Microevolutionary changes, however, don’t necessarily extend to support macroevolutionary changes (the creation of biological novelty through undirected evolutionary processes).

Microevolution is a fact. On the other hand, there are plenty of reasons to be skeptical of macroevolution.

¹ Sarah A. Tishkoff et al., “Convergent Adaptation of Human Lactase Persistence in Africa and Europe,” Nature Genetics 39 (2006): 31-40.
² J. Burger et al., “Absence of the Lactase-Persistence-Associated Allele in Early Neolithic Europeans,” Proceedings of the National Academy of Sciences, USA 104 (2007): 3736-41.

Since joining RTB in August 2005, I have devoted a fair bit of time trying to understand the latest ideas on the multiverse and how it impacts our apologetic arguments. I find it fascinating and complex and worthy of the effort to begin understanding the important issues—especially since the multiverse garners a lot of publicity.

Because of its popularity and its impact on RTB’s apologetics, I decided to devote one TNRTB a month to articulating and examining the multiverse idea. My intent is to lay out what I believe to be the most exciting, difficult to understand, and apologetically impactful issues in a clear and concise way. While I believe there are significant issues in multiverse models (described in coming articles), they are not inherently antibiblical. While it certainly affects the advancement of various arguments, the multiverse concept dramatically expands our view of reality and, I will argue, ultimately strengthens the case for the God of the Bible as Creator.

It would be hopeless to try covering all aspects of this complex topic in one sitting. So to get the ball rolling, some terminology is critical. The term “universe” describes all the space-time that exists whether—in principle—we could ever see it. In contrast, the “observable universe” contains only those regions of the universe where emitted radiation can reach some specified location—typically Earth. With a universe about 14 billion years old and our best measurements of its expansion history, our observable universe presently spans about 50 billion light-years. Inflation currently conceives of our universe existing within an inflating bubble of an “überspace.” If other bubbles exist containing other universes, these I will refer to as “bubble universes.” For most people, the “multiverse” refers to the ensemble of all bubble universes, although scientists use the term more broadly.

With this terminology, Max Tegmark’s multiverse overview provides a nice framework for further discussion. He organizes all multiverse models into four different levels, with higher-numbered levels being more speculative than lower-numbered levels.

Level I: There exist regions, beyond our observable universe but similar in size, which exhibit the same laws of physics but start with different initial conditions. Basically, this affirms that the universe does not end just beyond the most distant regions we can observe. The only controversial issue at this level pertains to the size of the region beyond our observable universe. If the universe is closed, the geometry of the observable universe (very close to flat) provides a minimum size for the whole universe of a few thousand times our observable universe. However, if the current formulations of how inflation works contain any truth, these models generically predict that the spatial extent of the universe is infinite.

Level II: There exist other bubble universes that obey the same equations of physics but with different fundamental constants, particles, and dimensionality. This level differs from Level I in that many universes (not just the one where we reside) actually exist inside their own inflating bubbles. Whereas all the regions outside our observable universe in Level I obey the same laws of physics with the same fundamental constants, each Level II bubble universe obeys the same laws of physics but the fundamental constants assume different values than those from our universe.

Level III: This level corresponds to the many-worlds interpretation of quantum mechanics put forth by Hugh Everett. The relevant feature of this level pertains to the physical basis for quantum events. When determining what happens at the quantum level, the best one can do is assign a probability for each of multiple different outcomes. Basically, the many-worlds interpretation says that for each quantum event, a “history” or “world” actually exists where each of the possible outcomes is realized.

Level IV: This level posits that any mathematically coherent structure defines a physical reality. Obviously, this leads to universes with completely different laws of physics. No Level V can exist because Level IV encompasses all possibilities.

Most of the scientifically and apologetically pertinent points arise in the Level I and Level II multiverses, so the bulk of what I discuss here will generally center on these two levels. Next time I will focus on how a Level I multiverse impacts probability-based apologetic arguments.

Through the centuries Christian thinkers have taken different positions on the controversial subject of war. Three broad theories concerning the morality of war for the Christian can be identified: activism, pacifism, and selectivism. Activism asserts that it is virtually always right to participate in war. Strict pacifism insists that it is never morally right to partake in war. Selectivism argues that it is sometimes right to take part in war.

Just war theory is a type of selectivism contending that while war is always tragic and often evil, it is sometimes morally right, just, and practically necessary. Some leading Christian advocates of just war theory have included Augustine of Hippo (354-430), Thomas Aquinas (1225-1274), and Francisco Suarez (1548-1617). Just war theory involves two main moral categories of evaluation.

1. Jus ad bellum (Justness of War)
   Concerning the moral justness of waging war, a just war must conform to the following moral considerations:

   A Just War will

   • Be waged by a legitimate authority (government or state, not private individuals)
   • Reflect moral deliberation (last resort after sincere diplomacy)
   • Have probability of success (reasonable belief that victory can be achieved)
   • Have a just cause (e.g., defense of innocents and freedom against direct aggression)
   • Be just in intent (establish peace, freedom, justice; not unlimited destruction of the enemy)
      

2. Jus in bello (Justice in war)
   Concerning the conduct of war, strategy and tactics must be just:

   A Just War will be conducted

   • With proper proportionality (sufficient, but not excessive force will be used; good should outweigh evil)
   • With proper discrimination (noncombatants [civilians or innocents] should not be targeted)

Just war theory has been criticized for various reasons through the years (e.g., by failing to appreciate the benefits of a preemptive strike, being unrealistic in its moral expectations, being practically unworkable), yet it nevertheless remains the most commonly accepted position among Christian thinkers when it comes to evaluating the moral considerations of waging war.

For further study on the ethics of war, see John Jefferson Davis, Evangelical Ethics, 3rd ed. (P&R Publishing, 2004) and J. P. Moreland and Norman L. Geisler, The Life and Death Debate (Praeger, 1990).