Letter from Cuba: "What you see here," visitors approaching the entrance the Zapata Swamp National Park in southwestern Cuba are told by a large billboard, "is the work of REVOLUTION."
This bald announcement must puzzle many of the foreign birdwatchers who travel here to see three species, a wren, a sparrow and a rail, which are endemic to the Zapata peninsula - that is, they are found nowhere else on Earth.
These creatures, the birdwatchers might say, are surely the work of revolution's infinitely more patient sister, evolution.
Tropical and subtropical islands - think Galapagos, think Hawaii - produce exceptionally large numbers of endemic plants, animals and birds. In isolation, new species find niches safe from predators and competitors which would have not allowed them to come into existence elsewhere.
Cuba is rich in endemics, with perhaps 4,500 plants and at least 23 birds unique to the island. The Cuban trogon, an exquisite, noisy and most approachable bird, had the perspicacity to evolve in the red, white and blue colours of the Cuban national flag, so that only the boldest of poachers would take a pot-shot at it today.
But the Marxist copywriters who created the billboard have a point, which is hammered home by further messages all along the drive through the park to the cobalt Caribbean seascapes at Playa Larga and Playa Girón.
Cuba's political revolution was also endemic and has remained more flexible, inventive and genuinely popular than the Soviet model to which it long looked for support. The Zapata peninsula has indeed witnessed that revolution at work, in several striking ways.
Firstly, it transformed the lives of the inhabitants, mostly charcoal-burners, whose poverty was miserable even by the appalling standards of pre-revolutionary Cuba. The poor greeted Fidel Castro's rebels as liberators from the hated Batista dictatorship, backed (until the last moment) by Washington and by the Mafia. Within two years of Castro's victory in 1959, illiteracy had been almost eradicated and a health service the envy of Latin America had been put in place.
These achievements help to explain the conclusion to the dramatic events on the Zapata peninsula in April 1961, when hundreds of heavily armed Cubans hostile to Castro swarmed on to Playa Larga and Playa Girón from the Bay of Pigs.
They had been transported from CIA training camps in Nicaragua and Guatemala, with the blessing of John F. Kennedy.
"This is where we stopped the mercenaries," another billboard tells drivers leaving the tiny village of Pálpite, just a few kilometres inland from Playa Larga. This sign is accompanied by one of many dramatic photographs from the 72-hour battle.
More can be seen at the impressive - though highly partisan - museum at Playa Girón. Castro's militias drove the invaders back to the sea, though at a very great cost in human life, touchingly illustrated by a little girl's shattered dancing shoes. Not for the last time, the CIA had disastrously miscalculated the level of popular support for a leftist government.
Every few hundred metres between Pálpite and Playa Larga, gleaming white pillars still exhort drivers to remember a revolutionary decalogue that sometimes seems to owe more to Christian than to Marxist morality: "never lie or violate ethical principles"; "modesty, selfishness, altruism, solidarity and heroism".
Whether such principles still carry much weight is impossible to assess, at least on a brief visit to a society which remains authoritarian. Cubans are understandably shy about speaking openly to foreigners about such matters.
What changes may come when the ailing Castro finally departs this life remains a mystery.
What is beyond doubt is that outrages like the Bay of Pigs invasion and the US economic blockade, which still causes such hardship in Cuba today, only serve to close ranks on the island against diktats from Washington or anywhere else. Cubans are genuinely proud of their leader's defiance of the imperious gringos.
Many non-Marxist Latin-Americans admire them for that, as I found in the unlikely context of a symposium on ecological restoration earlier in my visit.
At the Zapata swamp, the revolution's contribution to the conservation of a unique ecosystem is highly impressive. Even the rather conservative Smithsonian magazine has recognised Cuba's record in this field as the best in the Caribbean. In a market economy, the pressure from unscrupulous tourism operators on the peninsula's near-pristine beaches would be hard to resist.
Ironically, however, the swamp is today the victim of another kind of invasion. Alien plants like melaleuca are advancing far more successfully than the 1960s mercenaries and threatening the survival of the priceless flora and fauna.
Florida shares similar problems and there is cautious co-operation between dedicated scientists in both regions to solve the problem. In such joint efforts, perhaps, lies a hint of hope for a better future.