Predrag Slijepcevic from Brunel University in London and Nalin Chandra Wickramasinghe from Buckingham University on whether microbes such as bacteria can be the rulers of cosmic life
Are we alone in the universe? The famous Seti (Search for Extraterrestrial Intelligence) program has been trying to answer this question since 1959. American astronomer Carl Sagan, and many others, believed that other human-like civilizations must exist and that we could communicate with them . But skeptics are not convinced, arguing that the lack of evidence of such civilizations suggests they are extremely rare.
But if it is unlikely that other human-like civilizations exist, could there be other forms of life – perhaps better suited than us to spread across the cosmos? And would it be possible for such life forms to communicate with each other (non-human Seti)? Our new study, published in Biosystems, suggests he would. Microbes, such as bacteria, can be the rulers of cosmic life – and they are much smarter than we attribute to them. Indeed, we show how microbes could mimic the Seti program without human interference.
To understand germs, we need to challenge our anthropocentric biases. While many of us think of microbes as single-celled organisms that cause disease, the reality is different. Microbes are loosely organized multicellular entities. Bacteria, for example, live as member societies of several billion – colonies capable of “thinking” and making decisions.
A typical bacterial colony is a cybernetic entity – a “superbrain” that solves environmental problems. More importantly, all of the bacterial colonies on Earth are interconnected into a global bacterial supersystem called the bacteriosphere. This World-wide-web of genetic information has regulated the flow of organic elements on Earth over the past three billion years, in a way that will forever remain beyond human capacities. For example, they recycle important nutrients such as carbon, nitrogen and sulfur.
Even today bacteria are the most dominant living things on Earth. Remove bacteria from the biosphere and life will gradually collapse. Bacteria may therefore be much more suited to cosmic travel and communication than we are. A recent study discovered that terrestrial bacteria can survive in space for at least three years, possibly longer. Add to this the fact that bacteria can exist in a dormant state for millions of years, and it is clear that microbes are very resistant.
Indeed, different versions of the panspermia hypothesis – which declares that microbial life exists and travels throughout the universe – supports this notion. Recent mathematical models have supported this by showing that microbial travel may be possible not only in our solar system, but throughout the galaxy.
How could the microbial Seti work? We believe that the bacteriosphere could potentially mimic all of the known stages of human Seti. The first step in human Seti is the ability to read information on a cosmic scale. For example, using radio telescopes, we can analyze distant habitable planets. The second step is to develop technology and knowledge to assess whether habitable planets contain life. The third step is to announce our presence on Earth to intelligent aliens and attempt to establish contact with them if they respond to the initial signals.
Our version of microbial Seti is pictured below. Microbes have a limited ability to read information on a cosmic scale. For example, cyanobacteria can read the part of the electromagnetic spectrum coming from the Sun as visible light (first step). This biological phenomenon is called phototropism and occurs, for example, when a plant looks towards or away from the Sun or another source of light.
The second stage was crucial for the development of life on Earth. Cyanobacteria has developed biotechnology in the form of photosynthesis (which converts water, sunlight and carbon dioxide into oxygen and nutrients). This transformed the dead planet into a living planet, or the bacteriosphere, over a long period of evolution. Microbial life then became more complex, creating plants and animals over the past 600 million years. Yet bacteria remain the most dominant life form on the planet. Photosynthesis, as a form of bacterial technology, has always fueled life on Earth.
The third step concerns the attraction and communication between microbes with similar chemistries. Alien microbes should be able to integrate seamlessly into Earth’s bacteriosphere if they share carbon-based chemistry and metabolism, including DNA, proteins, and other biomolecules. The reverse process is also possible. Microbes from Earth could travel to space on asteroids and sow life elsewhere in the cosmos. Alternatively, humans, as future cosmic travelers, could act as microbial vectors under the human microbiome.
To appreciate the microbial Seti, we need to understand the concept of intelligence in the evolutionary sense. This will allow us to better assess bacterial intelligence, and its capabilities in the context of human and microbial Seti. Some biologists claim that human intelligence is just a fragment of a broad spectrum of natural intelligence that includes microbes and plants.
We also need to reassess technological signatures as signs of intelligent civilizations. Technologically advanced civilizations, according to the physicist Freeman Dyson, must have enormous energy needs. These demands can be met by building cosmic mega-infrastructures, called Dyson spheres, around their planets that can harness the energy of their host star. Searching for such spheres by looking to see if starlight is blocked could therefore be one way to find them.
But, if human-type civilizations are indeed rare, there is no point in search for such structures. Instead, it may be more appropriate to look for biosignatures as signs of microbial life on habitable planets.
The way forward in the search for extraterrestrial life may be to seek gases in atmospheres planets that signify life, such as oxygen, methane or phosphine, all of which are produced by microbes. The discovery of phosphine in the atmosphere of Venus was a promising lead, but now seems doubtful, as a new study suggests the signal could have been sulfur dioxide rather than phosphine. Yet we have no choice but to keep trying. Fortunately, the James Webb Space Telescope should be able to scan the atmosphere of planets orbiting stars other than our Sun when it launches later this year.