I've never heard of this gene, so I wasn't sure about the veracity of this claim…until the students and I started looking into it!
Student Responses
Almost all of the student responses cited the same manuscript, Suenaga et al. (2014). Others found subsequent manuscripts citing Suenaga et al. - and it seems that National Geographic had done the same, and made the same inaccurate interpretation of the original manuscript. You see…
Suenaga et al. mention in their abstract that "The NCYM gene is evolutionally conserved only in the taxonomic group containing humans and chimpanzees." However, this does not mean that it is found only in humans and chimpanzees, for two reasons. First, the interpretation of this quote depends on which "taxonomic group containing humans and chimpanzees" is being considered. This requires a little background on the relationships between primate species:
The closest related species to humans (genus Homo) is the chimpanzee (genus Pan). As shown above, these two genera (plural of genus) are the only two members of the tribe called Hominini. Thus, Hominini is one "taxonomic group containing humans and chimpanzees." However, if we go back farther in time, to the Homininae subfamily, then the "taxonomic group containing humans and chimpanzees" also includes the gorilla. Going farther back in time, to the Hominidae, we then include the orangutan. And so on.
Put bluntly, the authors did not write "in the taxonomic group only containing humans and chimpanzees" (which would indicate Hominini). Thus, other groups of species containing humans and chimps also exist.
To this point, some students noted that the same study later noted the following: they "identified orthologs for a probable NCYM protein in olive baboons, chimpanzees and pigmy chimpanzees. From here on, we focused on the NCYM gene of the hominidae to investigate the function of the protein product." So, they spent the rest of their analysis on Hominidae…and this group (see above) includes orangutans, gorillas, chimpanzee, and humans.
The authors just mentioned they identified orthologs (versions of the same gene) in baboons and chimpanzees. They did not say they found this gene in orangutans and gorillas (which, other than chimps and humans, are the only other species in the Hominidae). Thus, it is perfectly acceptable that they "focused on the NCYM gene of the hominidae" (which they only found evidence for in humans and chimps). This also explicitly ignores the fact that the authors themselves also said they found evidence for this gene in baboons, which (as shown above) are even less distantly related to humans than gibbons!
Put bluntly, there are two take-away lessons:
1) The authors have not deceived us, but we might deceive ourselves if we don't fully understand the terminology being used by the authors! and
2) Absence of evidence is not evidence of absence. This is one of my favorite quotes. It means that there are several potential reasons why the authors didn't detect the NCYM gene in closer relatives of humans than baboons. For example, it could be that the genome sequences of closer relatives (gorillas, orangutan) weren't of sufficient quality to identify the presence of this gene by computational methods. That wouldn't mean those species don't actually have the gene in question - it would just mean that we weren't yet able to find it!
Student Decision: Fact or Fiction?Fiction
Literature Cited
- Suenaga et al. (2014) "NCYM, a Cis-Antisense Gene of MYCN, Encodes a De Novo Evolved Protein That Inhibits GSK3b Resulting in the Stabilization of MYCN in Human Neuroblastomas" PLoS Genetics 10(1):e1003996.
