Why have we not discovered intergalactic alien life yet?

Enrico Fermi posited that a series of events need to occur for such advanced civilizations to emerge. Life must exist, Life must evolve to sufficiently complex organisms without going extinct, those complex organisms must form a civilization, that civilization must become sufficiently complex without going extinct, and so on.

When we multiply the products of these probabilities, we get the probability of any given planet having a civilization of that threshold level of complexity. There is an astronomically large number of planets in the universe, yet we have not encountered any extraterrestrial life, raising the possibility that perhaps one of these probabilities is a pinch point in the ascent of civilizations.

Here we sit, chatting on the internet as a civilization of hominids that spans the globe and has advanced technology capable of sending signals to the stars. Yet, there is no indisputable evidence of extraterrestrial life, and so while we wait for reassurance that civilizations can be made sustainable with high probability, it’s worth evaluating our own world for possible weaknesses.

Nuclear weapons seem like one such weakness. After we advanced science to the point of splitting atoms and releasing extremely large amounts of energy in nuclear reactions, our world of primates did what primates tend to do: we made weapons. We hominids are notoriously tribal – it’s a blessing and a curse. Tribalism is a blessing as our tribalism helped us form groups that formed societies, but it is also a curse in that at some level we inevitably seek differences, draw lines in the continental or social sand, and succumb to our proclivity towards distrusting people on the other side of the line. Countries developed nuclear weapons and pointed them at each other in an act of deterrence, letting other countries know of their mutually assured destruction in the event somebody crosses the wrong line.

Nuclear weapons have been around for a brief 80 years, and thankfully we seem to understand their consequences well enough to be sufficiently deterred from using them. These remain a significant threat to human civilization, but it’s possible they are not the answer to the Fermi paradox.

Another possible answer is less operatic, more tragic: disease.

In nature, all populations of all organisms everywhere are finite and bounded by common constraints that ecologists know and study well. Some organisms deplete their resources or pollute their environment, resulting in an inhibition of conspecifics that limits their population sizes. Famine. Others, especially top predators like lions and wolves, are competing over resources but often that competition is more brutally lethal and animals die in acts of intraspecific aggression. War. Lastly, some organisms have abundant resources and relatively little aggression towards conspecifics, but as they become numerically abundant so too do their pathogens. Pestilence.

Trees in the tropics are an example of a community whose populations are believed to be regulated by disease. If find an old growth tree in a tropical rainforest, look around your feet. Below is an old kapok tree that my friend Jacob Socolar and I stumbled upon while running vegetation transects in remote stretches of the Peruvian Amazon.

An old kapok tree like the one above has probably been alive for hundreds of years, and each year the tree reproduces and drops a rain of seeds onto the forest floor below. When you look at the floor, you can find a carpet of seedlings – tiny, baby kapok trees that are attempting to grow larger and reach the canopy. However, almost none of these seedlings are likely to survive. Why not?

It turns out, the old tree harbors an entire assemblage of species-specific arthropods and fungal pathogens. As the seeds rain down from the canopy so too do the species-specific arthropods and pathogens. While the parent tree might have discovered productive soils or aspects of a hill to which the species is well-adapted, seedlings of the same species of tree face an uphill battle as they try to reach the canopy while being bombarded with pathogens from their parents.

This article was written by  from the Alex WashburneBrownstone Institute