We were microbes before humans: what is LUCA?

From a microbe in the testicles to a person: LUCA's long journey

Every human being was once a single-celled organism swimming in fluid. This is not literary license: the spermatozoon is a cell with a flagellum that moves, consumes its reserves, and dies if it doesn't find its partner. From here begins a discussion that has been open for years and always leads to the same uncomfortable question: if we share an ancestor with cows, rats, and chimpanzees, what remains of the narrative that places us at the center of everything?

What is LUCA and why is it repeated in every generation

The acronym comes from the English last universal common ancestor. The thesis defended is that all known life descends from a single bacterium and that this process is not a remote episode: it is reproduced every time an egg and a sperm fuse. Whoever defends it goes further, maintaining that bodies are "walking ecosystems to protect the genome," with the ovary as the center and food as mere fuel to maintain the temperature of that ancestral sea.

The formulation is provocative, but the skeleton is the standard of evolutionary biology. What is striking is the packaging: the idea that we are still a worm, a tube of flesh with an entrance and an exit hole, not as an insult but as an anatomical description. If someone is bothered by it, the problem is not with the tube.

"Chance is not a force of nature": the current that rejects the lottery of evolution

Here the real sustancia ilegal opens. Faced with the orthodox Darwinian reading—random mutation plus natural selection—some argue in the thread that chance is not a force of nature, but a name for our ignorance. The universe would function like a chessboard: only moves permitted by the rules from the start are possible, and none are casual, because the possibility was already contained within the board itself.

The argument is supported by an old name, St. Augustine, and his rationes seminales: invisible germs of things that are already potentially made and develop—or not—according to the environment. Quantum physics would function as modern backing. And here the suspicion arises, pointed out by another intervention: replacing "the properties that govern matter" with the word God is changing the label, not the content. The discussion doesn't advance, it circles.

The leap from one cell to 30 trillion

An argument that is repeated against Darwinian orthodoxy is that of complexity: it is said that there is no proof that a single unicellular organism derives through natural selection and mutations into the 30 trillion perfectly organized cells of a human body. The objection is not absurd in its formulation—no one has filmed that specific leap—but it confuses the absence of a complete record with the absence of a mechanism. It is the classic appeal to the gap.

Do animals have their own civilizations?

Another line of the subject is that which maintains that we call a landscape what are actually societies. Ecosystems have been functioning for millions of years without veterinarians, ecologists, and humans. It is argued that each species communicates in its own universe and that what we perceive in captivity—the animal eating, defecating, and fleeing—is the behavior of a prisoner, not that of a free being in its environment.

This is the most debated part and the one that provides the least evidence. The proliferation of recordings with mobile phones is cited as evidence, although the leap from "complex behavior" to "civilization" remains an act of faith, not a fact.

Creationism, on the ropes

For the creationist faction, evolution is not science but "a mental absurdity," and their star argument is that a house does not descend from bricks just because it is made of them. The answer is always the same: genetics and the fossil record do not ask if the origin is pretty, they just describe what is there. And there is a phrase that summarizes the struggle: "We came from a fish that came out of the water and didn't die."

In the end, any of the more radical stances return to the same point: we are still a tube of flesh with an entrance and an exit hole. The only thing that changes is what we decide to believe happens in between.