The Platypus Terrorizes Evolution

The puzzling platypus was discovered long before Charles Darwin published The Origin of Species. This duck-billed oddity is like a mammal, a bird, and a reptile all in one species.

When the platypus, nicknamed the “watermole,” was first discovered in 1797 by early European settlers near the Hawkesbury River, outside Sydney, it triggered a lasting controversy. The perplexed local governor, Captain John Hunter, sent specimens back to Mother England for study.

The “watermole” was equally mystifying in England. Zoologists George Shaw suggested it was a “freak imposture” sold to gullible seamen by Chinese taxidermists. Suspecting fraud, they tried to pry the “duck’s bill” off of the pelt, leaving marks on the bill that are still visible today at the British Museum in London.

In 1802, an English scientist confirmed that the creature was neither freak nor fraud, and he labeled the specimen “platypus” because of its flat bill and gave it the scientific name Ornithorhynchus anatinus. Since then, the platypus has stood as an iconic conundrum in natural history.

While voyaging on the HMS Beagle in 1836, Charles Darwin recorded his encounter with a platypus, during his travels along Coxs River near the Wolgan Valley in Australia:

In the dusk of the evening I took a stroll along a chain of ponds, which in this dry country represented the course of a river, and had the good fortune to see several of the famous Ornithorhynchus paradoxus. They were diving and playing about the surface of the water, but showed so little of their bodies, that they might easily have been mistaken for water-rats. Mr. Browne shot one.

At the time,  the Platypus official name was Ornithorhynchus paradoxus due to the paradoxical evolutionary status by Johann Blumenbach in 1800 then, later changed to Ornithorhynchus anatinus in 1934 to avoid the evolution controversy.

Not only do these furry animals actually lay eggs like a bird, the young feed on breast milk like a mammal and make venom like a snake. Although the platypus has been an evolutionary conundrum, the structure of the platypus genome has now been deciphered. In comparing the platypus genome with genomes of the human, mouse, dog, opossum, and chicken, researchers found that the platypus shares 82 percent of its genes with these animals.

For egg production, the platypus genome matches for the ZPAX genes that had previously been found only in birds, amphibians, and fish, and it shares with the chicken a gene for a type of egg-yolk protein called “vitellogenin.” For breast milk production, the platypus has genes for the family of milk proteins called caseins, which map together in a cluster matching humans. Lastly, the male platypus has spurs on its hind legs loaded with lethal venom, rising from duplicate reptilian-like genes.

The platypus exemplifies how similar genes in different species produce the same function. The question is how does genetic identification clarify the evolutionary place of the platypus? The answer is it does not.

According to Richard Gibb, Director of the Human Genome Sequencing Center at Baylor College of Medicine in Texas, concluded, “there is nothing quite as enigmatic as a platypus. You have got these reptilian repeat patterns and these more recently evolved milk genes and independent evolution of the venom. It all points to how idiosyncratic evolution is.”

Darwin proposed in The Origin of Species that as new species arise through “successive, slight changes,” there is corresponding extinction. Darwin wrote “extinction and natural selection go hand in hand.” The evidence however points to the conservation, not the extinction of variations.

A team led by Gregory Hannon of Cold Spring Harbor Laboratory in New York sequenced microRNAs, which regulate gene expression, from six platypus tissues, and also found a mix of reptile and mammal similarities, concluding that we “have microRNAs that are shared with chickens and not mammals as well as ones that are shared with mammals, but not chickens.

Classifying the platypus into an evolutionary paradigm has been a challenge. In 1992, Australian biologist, Michael Archer wrote, “Indeed, evolutionary scientists are baffled about the ancestry of the platypus.”

As baffling as the platypus was in 1992, it is even more so today, despite the availability of genomic sequencing. Francis S. Collins, past Director of the National Human Genome Research Institute, concedes: “At first glance, the platypus appears as if it was the result of an evolutionary accident. But as weird as this animal looks, its genome sequence is priceless for understanding how mammalian biological processes evolved.”

In a 2008 BBC interview with Helen Briggs, geneticist Mark Batzer, from Louisiana State University notes: “One big surprise was the patchwork nature of the genome with avian, reptilian, and mammalian features.”

What is missing from Collin’s “priceless for understanding” is how the platypus fits into the Tree of Life sequence as Darwin envisioned. No wonder Darwin struggled with the platypus knowing that it contradicting his theory of natural selection—the Platypus should have become extinct. In a 1860 letter to Charles Lyell,  Darwin explains that the

I quite agree with you on the strange and inexplicable fact of Ornithorhynchus having been preserved.

Even in the context of the gene-centric Modern Synthesis theory, genetics seems to play an array of confounding evolution roles. In the butterfly, similar genes are associated with different forms and functions. In the octopus, different genetics results in similar forms and functions. In the platypus, the same genes in different species are associated with the same functions.

Genes are independent, not sequential. As Richard Gibb points out in the Nature journal, it “all points to how idiosyncratic evolution is.”

In Notebook D, Darwin wonders, “when will Ornithorhynchus come in circle?” noting, “Such difficulties will always occur if animals are thought to have been created.” For Darwin, his theory followed an ideology, not the scientific evidence.

After 150 years since the publication of The Origin of Species, the Platypus continues to strike terror in the evolution industry. Jerry Coyne, the consummate neo-Darwinist, in Why Evolution is True never even mentions the Platypus—for good reasons.

According to Alan Love of the University of Minnesota, in Evolution, The Extended Synthesis, published by The MIT Press, “The vigor of these kinds of controversies has led one researcher [Massimo Pigliucci] to ponder whether an extended evolutionary synthesis is just around the corner or simply an impossible chimera.”

Evolution was once a theory in crisis, now evolution is in a crisis without a theory.

References available upon request

 

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