188 | Arik Kershenbaum on What Aliens Will Be Like

Episode Summary

Executive Summary: Sean Carroll and zoologist Arik Kirschenbaum debate how much can be inferred about extraterrestrial life from Earth’s evolutionary history. The conversation argues that while alien life will almost certainly differ in detail, physics, natural selection, and convergence may make complex, animal-like, language-capable, technological life more common than pure speculation suggests—though Carroll remains skeptical about advanced civilizations.

Main Topics: Evolutionary convergence vs contingency (Priority: 5/5): The discussion opens with Stephen Jay Gould’s 'rewind the tape' idea and whether evolution would recreate similar forms. Kirschenbaum argues that physics and repeated selective pressures make some outcomes—like limbs, symmetry, and flight—likely to reappear even if exact histories differ. Life beyond Earth and the prevalence of simple life (Priority: 5/5): Kirschenbaum is optimistic that life exists elsewhere and says most of it will likely be simple, microbial 'slime.' He points to the sheer number of Earth-like planets and the commonality of water and habitable conditions as reasons to expect widespread life. Transitions to complexity: multicellularity, predation, and the Cambrian (Priority: 5/5): The interview treats the emergence of multicellular life as a major bottleneck. Kirschenbaum links the Cambrian explosion to new ecological interactions—especially predation—that created niches for shells, eyes, teeth, and other complex adaptations. Intelligence, language, and technology (Priority: 5/5): Kirschenbaum distinguishes general animal intelligence from human-like intelligence. He argues that language as an unlimited concept-generating system likely emerged from social conflict and coordination, and that technology is closely tied to that linguistic capacity. Alien morphology and communication (Priority: 4/5): The pair discuss likely alien body plans: bilateral symmetry, limbs, and perhaps recognizable animal-like organization. Communication channels are tied to environment, with sound, light, or electric fields favored depending on medium and constraints. Alien sociability, friendliness, and contact risks (Priority: 4/5): The final section asks whether advanced aliens would be cooperative or dangerous. Kirschenbaum argues interstellar colonialism is unlikely to motivate star-faring beings, while Carroll remains cautious and notes the uncertainty of whether advanced civilizations are common at all.

Key Arguments: Physics sharply constrains biological form, making repeated evolution of solutions like limbs, bilateral symmetry, and flight plausible across planets. Most extraterrestrial life, if found, will probably be simple microbial life because complex life took most of Earth’s history to emerge. The Cambrian explosion suggests that once predation and ecological interactions appear, complexity can rapidly diversify through natural selection. Human-like intelligence is likely rooted in social competition, alliance-making, and language rather than intelligence in a broad generic sense. Language should be defined as the ability to communicate an unlimited number of concepts; that capacity appears uniquely human on Earth. Technology likely requires both language and manipulable anatomy, but opposable thumbs are not strictly necessary; different body plans could still build tools. Communication modes will depend on the environment: sound in dense atmospheres, light in transparent media, electric signals in water or special contexts. Advanced alien societies, if they exist, may not be hostile because interstellar travel would imply such abundance that conquest would be unnecessary. There may be no federation of advanced civilizations because the search effort has been limited and advanced life may be rare or short-lived.

Data Points: Earth-like planets in the galaxy: 10 to 40 billion - Kirschenbaum cites current estimates to argue that habitable worlds are abundant. Time life existed on Earth before complex multicellular organisms: Most of Earth’s history - Used to support the claim that microbial life should be far more common than complex life. Estimated delay to multicellularity: A couple hundred million years - Kirschenbaum says early multicellular life took a very long time to become recognizable complex life. Cambrian explosion date: 540 million years ago - Referenced as the period when major body plans and ecological complexity rapidly diversified. Times flight evolved on Earth: At least four times - Birds, bats, pterosaurs, and insects are given as examples of convergent evolution. Human-like social intelligence duration: About 800 million years - Kirschenbaum claims animals have had intelligence since they existed, roughly this long. Duration of deliberate radio leakage: 100 years - Used in the argument that technologically advanced civilizations would already know Earth exists.

Pivotal Quotes: "Sooner or later, someone's going to take a bite out of someone else, and then all bets are off." — Arik Kirschenbaum: He uses this to summarize why predation drives ecological complexity. "I don't know what you mean by intelligence, but animals have been intelligent ever since they've existed." — Arik Kirschenbaum: A key definition shift away from human exceptionalism toward broader animal cognition. "If you can travel from one star to another, you can make as much stuff as you want, you can make as much food as you want." — Arik Kirschenbaum: Part of his argument that interstellar colonialism is unlikely to be a major alien motive.

Implications: Listeners should expect alien life, if found, to be mostly microbial at first, but not dismiss the possibility of convergent animal-like forms, social intelligence, and even technology. The big uncertainty remains how often biology crosses the rare thresholds to complexity and civilization.