When people speculate about what alien life forms might look like, most experts think it is extremely unlikely that they will be anything like humans. Neil deGrasse Tyson has critiqued Star Trek for its “lack of imagination” by making all their alien species somewhat humanoid in form with only slight cosmetic differences (although that was probably more due to lack of finances rather than lack of imagination). Regardless, I think experts like NDT are wrong. Intelligent aliens, if they exist, will probably look somewhat similar to humans, as Star Trek portrayed.

The experts believe aliens will look vastly different because of the vastly different environmental conditions that would exist on other planets. It is therefore inevitable that life would evolve in a drastically different way, so that the resultant alien life forms would look drastically different. And that is true…to an extent. The process of evolution on planet Earth resulted in life forms that look vastly different, such as a worm, a frog, a tiger, an octopus, an eagle, and an elephant. These creatures are indeed drastically different, and they’re only a microcosm of the biodiversity on the planet.

On alien planets, we would no doubt see similar biodiversity of wildly different creatures evolving in the various environmental habitats on those planets. But on Earth, only one of the billions of species evolved into an intelligent life form that invented a technological civilization. When we talk about searching for alien life, that is what we are really searching for—an intelligent life form capable of creating a technological civilization. Not just life, but human-like life that is sapient.

There could exist alien planets similar to Earth before humans existed—alien planets full of life forms like dinosaurs. That would be quite interesting to study from a scientific perspective, just as we study animals on Earth. But that wouldn’t really change anything about what it means to be human. It would only make humans more special in the grand scheme of the universe.

The search for extraterrestrial life is really a search for intelligent alien life. It’s a search for technological civilizations built by life forms as smart or smarter than humans. If such alien life forms exist, I would surmise that they do look somewhat similar to humans. Because of convergent evolution.

It was the unique evolutionary adaptations of homo sapiens that enabled us to create a technological civilization. Those adaptations include bipedalism, opposable thumbs, larger brains, mouths and vocal cords to speak and create language, and living on land to create fire. All those prerequisites were needed to create technology—and we were the only species on Earth to have them all. Perhaps other hominid species could have done the same, but we sapiens outcompeted them. Regardless, no other life form on Earth, despite all their diversity, has been able to come anywhere near the technological capacity of human beings. We are the only Terran species with a space program to potentially contact alien species.

For alien life forms to do the same, they would need to meet those same evolutionary prerequisites. If life exists on alien planets, it is likely that evolution would converge toward a humanoid species. Or rather, it is not inevitable that a humanoid species will evolve (as one did not on Earth for millions of years during the reign of dinosaurs), but it is inevitable that if an intelligent life form capable of inventing a technological civilization evolves, then that species would likely be humanoid. Not that they would be the same species as us, but as in Star Trek, they would have a general humanoid appearance: being bipedal, with arms, legs, a head, mouth, eyes, ears, and mouth.