5 sci-fi aliens - and the likelihood they could actually exist

"The diversity of life on our planet is amazing, especially considering it all begins with essentially the same ingredients - every cellular organism that has ever existed, from bacteria and birch trees to dinosaurs and humans, is built on DNA-based biochemistry. But how much more diverse might life be on other worlds? Planets with different geology and chemistry, orbiting different types of stars, could yield an endless variety of life-forms."

"You can immediately tell that E.T., the Na'vi people in Avatar, and most of the gang at the Star Wars cantina are not from Earth, but they still have recognizably human features: two arms, two legs, two eyes, and faces that convey familiar emotions. The only obvious difference between Mr. Spock - the Vulcan science officer from Star Trek - and your next-door neighbor is that the former has pointy ears and eyebrows that suggest a constant state of surprise."

"In reality, a human-like form is probably the least likely for an extraterrestrial. Even if evolution started over here on Earth, we wouldn't necessarily end up with the exact same intelligent bipedal primates (us) at the top of the food chain. In fact, no particular body plan seems to be favored by biology, though most animals are anatomically symmetrical. The evolutionary reason for that, according to a 2022 study, is that symmetry requires less information for DNA to encode and allows more flexibility for developing"

Life on Earth exhibits remarkable diversity yet is universally based on DNA biochemistry across cellular organisms. Planets with different geology, chemistry, and stellar environments could foster very different biochemistries and morphologies, producing an enormous range of life-forms. Science fiction often portrays humanoid aliens with familiar limbs and faces for relatability, but human-like body plans are probably unlikely elsewhere. Even if evolution occurred on Earth independently, it would not necessarily produce the same bipedal primates. Most animals display anatomical symmetry because symmetry requires less genetic information to encode and provides greater flexibility during development, according to a 2022 study.

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