sapiens
Explanation
The Joke
A child asks an adult why humans are called "Homo sapiens sapiens" (the full trinomial name for modern humans). The adult explains that when he was a kid, it was just "Homo sapiens," which means "wise man." The child then asks why the second "sapiens" was added. The adult's answer: "To make it clear that the first one was ironic." The final panel shows the child saying "Ahhh" in understanding, with both figures shown in silhouette against a night sky.
The Humor
The joke is a sardonic commentary on human nature. "Homo sapiens" literally translates to "wise man" in Latin, and our species' taxonomic name essentially flatters us by calling us the wise ones. The comic suggests that humanity's track record has so thoroughly disproven this self-congratulatory label that a second "sapiens" was needed -- not to emphasize our wisdom, but to signal that the whole thing is sarcastic. In reality, the subspecies name "Homo sapiens sapiens" was introduced to distinguish anatomically modern humans from other subspecies like Homo sapiens neanderthalensis, but the comic's explanation is far funnier. The gag taps into a long tradition of misanthropic humor about how poorly humanity lives up to its billing as the "rational" or "wise" species.
References
"Homo sapiens" is the binomial name given to modern humans by Carl Linnaeus in 1758. The trinomial "Homo sapiens sapiens" is used in some taxonomic frameworks to distinguish anatomically modern humans from archaic human subspecies. The word "sapiens" derives from Latin "sapere," meaning "to be wise" or "to have sense."