Do Self-Replicating Protocells Undermine the Evolutionary Theory?
It’s remarkable to think that two people can examine the same facts and arrive at vastly different conclusions, yet this is what’s happening as people interpret advances in synthetic biology. Researchers are striving to create protocells—chemical supersystems with the properties of life—and many conclude that if scientists can produce cell-like entities in the lab, then they will be that much closer to understanding how evolutionary processes generated the first life-forms. But will this development actually benefit evolutionary theory?
A team of Japanese researchers has created protocells with the capacity to self-replicate continuously for multiple generations, mimicking the behavior of biological cells.1 Specifically, these scientists formed vesicles that they could stimulate to grow and divide. More impressively, they were able to couple the replication of DNA in the vesicles’ internal compartment to the growth and division process. They even devised a way to replenish the daughter vesicles with nutrients after cell division took place so that these newly formed entities, in turn, could grow and divide. These researchers concluded that their work “demonstrates how collaborative dynamics emerged from nonliving matter under certain circumstances.”2 In other words, these scientists see their work as supporting an evolutionary explanation for the origin of life. In their report, the Japanese scientists even go so far as to assert that a system such as the one they devised in the laboratory could have emerged near hydrothermal vents on early Earth.
Yet I interpret the results of this study very differently than the Japanese scientists and many others in the scientific community. In my view, their work undermines the evolutionary paradigm. It provides empirical evidence that an intelligent agent must play a crucial role in the transformation of nonliving material into cell-like entities.
To produce protocells with the capacity for multigenerational self-replication, the researchers had to devise a sophisticated strategy that required extremely knowledgeable and skilled scientists to execute the experiment under highly controlled conditions in the laboratory. For example, the researchers had to carefully select the right types of phospholipids (PL)—the molecules that play a key role in forming cell membranes—to form stable vesicles. They also designed and manufactured two synthetic, nonbiological lipids with specialized properties. These lipids played a key role in coupling DNA replication to vesicle growth and division. One of these lipids, dubbed a catalyst (C), was added to the two PL species used to form the initial vesicle population. The researchers had to carefully adjust the initial PL and C compositions to form stable vesicles that would then be capable of growing, dividing, and becoming tied to DNA replication.
Next, the scientists encapsulated (1) nucleotides (dNTPs, the building blocks of DNA); (2) single-stranded DNA; (3) carefully designed DNA primers; and (4) a special type of DNA polymerase (an enzyme that replicates DNA) into the vesicles’ interior compartment. This encapsulation process required the researchers to implement an exacting laboratory protocol that involved drying the lipids so that they formed a film and then rehydrating the film (with a solution containing the dNTPs, single-stranded DNA, DNA primers, and DNA polymerase), followed by incubation under a precise set of conditions.
Once the materials for DNA replication were encapsulated, the researchers carefully heated the vesicles, triggering DNA replication. Once produced by the replication process, the newly formed DNA molecules were automatically absorbed into the interior walls of the vesicles. This binding took place because the lipid catalyst (C) was designed to possess a positive charge, triggering its interaction with negatively charged DNA.
After cooling down the system, the researchers added another carefully designed synthetic lipid (V) to the vesicles. The C reacted with the V, converting it into a derivative material that caused the vesicles to grow and become destabilized. The destabilization caused the vesicles to fissure into two daughter vesicles.
In the next step, the researchers replenished the newly formed daughter vesicles with dNTPs so that the next round of DNA replication could take place. They accomplished this feat by encapsulating the dNTPs in vesicles dubbed conveyor vesicles. The lipid composition of these vesicles had to be carefully adjusted so that they possessed a negative charge on their surface. The negative charge made it possible for the conveyor vesicles to fuse with the daughter vesicles, which were designed to possess a positively charged surface. The fusion events were triggered by a dramatic change in solution pH, orchestrated by the researchers. The researchers also had to carefully adjust the amount of the C in the conveyor vesicles so that when they fused with the daughter vesicles, the newly formed DNA would bind to the membrane wall of the daughter vesicles, allowing the cycle of growth and division to repeat.
As a biochemist, I can’t help but to be impressed with the ingenuity of their work. This study exemplifies science at its very best. But does it explain how life originated?
Even though the Japanese scientists see their research efforts as providing support for a chemical evolutionary origin of life, their own description of the work betrays their convictions. They write: “To achieve this goal, we selected well-defined suitable lipids and macromolecules, including newly designed ones, and constructed a giant vesicle (GV)-based model protocell that links self-replication of information molecules (RNA/DNA) with the self-reproduction of a compartment (GV)” (italics added).3 These scientists can’t avoid using design language because the self-replicating protocells they produced were intelligently designed.
It is hard to envision how a system such as the one the Japanese scientists devised could have ever emerged on early Earth through unguided evolutionary processes. And in light of this work and other studies in synthetic biology, it is also difficult to imagine how anyone could conclude that life emerged via chemical evolution. But they do. Still, in my view, the facts speak for themselves: work in synthetic biology affirms the case for intelligent design.
- For a more in-depth look at my views on the quest to produce artificial life, please read Creating Life in the Lab.
- Kensuke Kurihara et al., “A Recursive Vesicle-Based Model Protocell with a Primitive Model Cell Cycle,” Nature Communications 6 (September 2015), doi:10.1038/ncomms9352.