Q: Do species which have a closer common ancestor to humans tend to be more intelligent?

Our closest living relative, the chimpanzee, seems to be regarded as intelligent:

Chimpanzees make tools and use them to acquire foods and for social displays; they have sophisticated hunting strategies requiring cooperation, influence and rank; they are status conscious, manipulative and capable of deception; they can learn to use symbols and understand aspects of human language including some relational syntax, concepts of number and numerical sequence; and they are capable of spontaneous planning for a future state or event.

Does this hold in general? And, if so, how strong is the correlation?

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    $\begingroup$ humans being more intelligent than other animals is a hotly debated topic :-D huffingtonpost.com/2013/12/11/… $\endgroup$ – The Last Word Jul 9 '14 at 5:15
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    $\begingroup$ I agree with point 1 in Remi.b's answer; what do you mean by intelligence? Generally though, no it doesn't. Crows have tools, octopuses and goldfish solve puzzles, dogs respond to human voices, whales have language. There are too many exceptions to say that 'generally' the closer to humans the more "intelligent" the species. And who said we're top of the "clever test"? Could you do this? independent.co.uk/news/science/… $\endgroup$ – James Jul 9 '14 at 15:41
  • $\begingroup$ Probably not. Ravens can solve multistep problems, showing some level of premeditation. Border Collies have been shown to associate over 1000 human words with specific objects. Dogs are one of the only animals able to interpret pointing by humans, and their brain responses in fMRIs to photographs of strangers to owners (Loved ones), shows pretty much the same patterns as humans exhibit. Pigs are believed to be one of the only animals other than humans that have self recognition when looking at their reflections in a mirror. Dolphins and whales probable have language. Gorillas do sign language. $\endgroup$ – AMR Jan 1 '16 at 15:32

Several issues here that make your question unanswerable:

  1. Intelligence is not defined. How would you define it?
  2. What kind of relationship are you exactly looking for? Comparing average intelligence between groups or trying to fit a regression with intelligence on the Y-axis and relatedness to human on the X-axis?
  3. The general issue hidden behind methods of species comparison is "How do you define a species?"

If you want to compare average intelligence between groups, meaning that you want to compare average intelligence of a group of closely related species of human to the average intelligence of all animals? Then the answer to your question will probably be "Yes" as primates seem in average to be more intelligent than the average animal and mammals tend to be in average more intelligent than the average animal. I'd expect too that vertebrates are probably on average more intelligent than the average animal. Let's not forget that some animals have no brain (e.g. Sponge).

But now if you want to fit a regression between intelligence and relatedness to human for all animals, you will probably have some trend (a regression with a significant slope (positive correlation)), but you will have many group of points that will not fit on your line. Many birds for example may be considered as much more intelligent than humans depending on your definition. Many invertebrates such as octopuses are very intelligent, too. If you allow for a broad definition of intelligence, then you may also consider the intelligence of social insects which may be surprising. Some aquatic mammals are very intelligent although other, more seemingly stupid mammals, are closer to humans than aquatic mammals.

In short, keep in mind that intelligence is not easy to define, and depending on the definition, the answer will be different. Typically, if you use a very human-like definition of intelligence, you will probably find that intelligent species are more closely related to human. There is a correlation between intelligence and phylogeny (=tree of life), therefore yes, closely related species to humans may have some tendency to be fairly intelligent, but there are many other clades (groups of species on a phylogeny) that show some impressive intelligence, especially in insects, in mollusca, in birds, the carnivora and the cetacea.


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