Intelligence Evolved at Least Twice in Vertebrate Animals

Evolution, Fitness, and Intelligence

• Several comments stress that natural selection optimizes “fitness to the current environment,” not raw intelligence; intelligence is costly and only persists when benefits outweigh energy, mass, and developmental tradeoffs.
• There’s debate over whether “survival of the fittest” is trivial or circular versus a useful shorthand for “genes with higher reproductive success become more common.”
• Intelligence is framed as an “endgame” adaptation that doesn’t dominate because many niches are better filled by specialists or brute-force reproduction (e.g., flies).

Bird vs Mammal (and Other) Brains

• A major thread explores why birds achieve high intelligence with much smaller brains:
  • Higher neuron density and shorter neurons (more neurons per volume, faster signaling).
  • Strong selection for light, compact brains due to flight; plus efficient lungs and mitochondria.
• Birds are seen as “die-shrunk” brains relative to mammals; some suggest a human with bird-like neurons would be astonishingly capable.
• Not all birds are smart; generalist, playful, highly social species (corvids, parrots) stand out, paralleling primates and some wasps.
• Octopuses and cephalopods are cited as an independent invertebrate route to complex cognition.

Sociality, Language, and Intelligence

• Many argue runaway intelligence often comes from social arms races: tracking cheating, alliances, deception, and reputations (in birds and humans).
• Others suggest visual demands (especially in flying animals) and complex environments also drive neural complexity.
• Discussion distinguishes rich communication from true language with open-ended compositionality; some think only humans (and maybe a few other hominins, LLMs, and possibly bonobos) clearly cross that threshold, though some bird species may be close.

Breeding and “Uplifting” Animals

• Commenters discuss selective breeding for intelligence in parrots or dogs, noting likely tradeoffs (aggression, fertility, disease) and ethical concerns once animals become more self-aware and short-lived.
• Disagreement arises over whether genetic tradeoffs are inevitable or just common in practice.

Defining and Detecting Intelligence

• One camp uses a pragmatic definition: building internal models to predict and plan.
• Another criticizes neuroscience for “neurobabble,” arguing that terms like intelligence, abstraction, “best,” and “optimal” smuggle in unexamined philosophical assumptions and teleology.

Cosmic and Deep-Time Implications

• Multiple, independent evolutions of complex brains (birds, mammals, cephalopods) are taken by some as evidence that intelligence isn’t vanishingly rare, boosting the “intelligent life” term in the Drake equation.
• Others note uncertainties in fossil inference and timelines, and speculate about past or hypothetical non-human civilizations, but treat these ideas as speculative.