The (Not So) Universal Genetic Code: Evidence for Evolution (Part 7)

“All forms of life use the same genetic language of DNA and RNA,” pointed out my first-year biology textbook, “and the genetic code is essentially universal. Thus, it is likely that all species descended from common ancestors who used this code.”1

Well, thought my first-year self. That sounds reasonable. If all living things evolved from one ancestor, they surely would share similar blueprints and building blocks. According to my textbook, they do. Does this mean Genesis, which teaches that God created living things “according to their kinds” and fashioned humans in His image, must be wrong?

God’s word is infallible, so the short answer is no.2 But a little critical thinking reveals why. To find out how, it’s essential to first understand the way genetic language works.

A Bit of Background Science

How does DNA encode information to build and maintain all living things? The secret lies in the arrangement of nucleotide “letters” along a DNA strand. Two strands wind together to create a double helix which looks like a twisted ladder, with paired nucleotides comprising the ladder’s “rungs.” The four nucleotides, A, T, G, and C, always pair up as A with T and G with C.

Genes, which are like messages written in nucleotides, encode proteins—molecules responsible for almost all the work in the cell. Amazingly, one nucleotide sequence can contain information for multiple genes, depending on which sections of information are copied and spliced together. To make proteins from genes, an array of other proteins works together to produce messenger RNA (mRNA) composed of nucleotides complementary to the template gene’s nucleotides.

Each set of three nucleotides along an mRNA strand is called a codon. Individual codons code for specific amino acids, which are the building blocks of proteins. Other molecules called tRNA “read” codons to add amino acids in the right sequence to build a specified protein. “Stop” codons, meanwhile, tell certain tRNAs where to stop adding amino acids. (Sophisticated, hey?)

Most—but not all—living things use the same codons to code for specific amino acids or “stop” signals. That’s what’s meant by “universal genetic code.”

Breaking Down Arguments

With this background in mind, we can think through the “universal code” argument using Critical Thinking Check 6.

1. Identify the Observational Science

The facts we can observe in the present are that DNA encodes all known life forms’ genetic information, and most living things use the same genetic code. But certain bacteria, protists, yeast, algae, and the mitochondria in your cells use typical stop codons to code for amino acids or show other differences to the usual code.3 There are additional exceptions as well, which is why my textbook didn’t call the code completely universal.

2. Identify the Historical Science

The story my textbook constructed about the past says all living things descended from common ancestors who used the standard code. Many evolutionists still say, “a single common ancestor.” But other researchers such as Dr. Craig Venter, lead inventor of a synthetic bacterial genome, challenge the notion of one evolutionary “tree of life.”4 That’s because the genetic code is not universal, as evolutionists once predicted. One evolutionary research team explained,

At present, there are known considerable numbers of departures from the “universal” code in the nuclear as well as the mitochondrial codes…It is therefore misleading to think that “the genetic code is strikingly (or nearly) universal, but there exist some exceptions”. Such a description may be found in many textbooks. In reality, the genetic code is obviously not universal, and the deviant codes should not be treated as mere exceptions.5

As other researchers pointed out, “Any change in the genetic code alters the meaning of a codon, which, analogous to reassigning a key on a keyboard, would introduce errors into every translated message.”6 In other words, changes like reassigning stop codons to code for amino acids would affect the entire organism, adding deleterious mutations all throughout its genome.

Furthermore, how would a stop codon become reassigned? You’d have to not only change the relevant tRNA but also somehow replace all the reassigned stop codons with recognized ones. As some have pointed out, experiments which try to replicate these steps require researcher intervention and foresight—in other words, intelligent design. So, changing the genetic code even once doesn’t fit what we know from observational science.

3. Identify the Assumptions

Whether people suggest the code evolved once or multiple times, what other assumptions lurk behind these historical science interpretations? Besides assuming evolution can transform one kind of creature into another, these explanations suppose functional, interpretable, informative codes can emerge from unguided processes. (For more about the problems with these assumptions, check out articles on information theory, life’s origins, mutation, and natural selection.)

4. Identify Alternative Explanations

Given the issues with evolutionary assumptions, what’s another explanation for most living things’ common genetic language? They have the same Designer. We wouldn’t expect that Designer to invent separate codes for different creatures any more than we’d expect authors to create new languages for every book they write or software engineers to develop new coding systems for each computer program.

Because the Designer engineered living things to interact with each other, it’s also understandable why different life forms contain the same building blocks. Plant DNA, for instance, encodes information to help plants manufacture the sugars and proteins our cells need for energy and amino acids.

5. Identify the Rest of the Story

What other facts support a different explanation from the textbook’s? Besides the fact that evolution doesn’t predict a non-universal code, the reality that DNA is like a language or coding script points to a Designer. This is especially true because genetic language seems to use about the best code possible for protecting against errors. According to some researchers, the standard genetic code “achieves between 96% and 100% optimisation relative to the best possible code configuration.”7 And it makes sense for a good Designer who designed an optimal code to apply that code to many different organisms.

A Final Check on Logic

Even if the code were universal, Critical Thinking Check #7, Check the Logic, shows the trouble with arguments claiming a “universal code” means evolution is true:

If evolution is true, most life forms should use the same genetic code.
Most life forms do use the same genetic code.
Therefore, evolution is true.

This is a case of Affirming the Consequent, a fallacy we’ve seen in previous arguments. It’s logically invalid because its conclusion doesn’t necessarily follow from the premises. That is, there could be other reasons for a “universal” code besides evolution—like optimal design. And sure enough, a close look at the observational science reveals that neither the genetic code nor its exceptions support an evolutionary explanation. Rather, like Romans 1:20 says, life’s genetic language reveals the attributes of its Creator.

For more on how to think critically about any faith-challenging message, stay tuned for future blog articles and my new video series, CT (Critical Thinking) Scan, available now on the AiG Canada YouTube channel and the AiG Canada Facebook page.