This method measures "intelligence directly with a battery of cognitive tests rather than relying on proxies like relative brain size.
For example, apes, humans, and cetaceans most likely had a common ancestor with high levels of cognition, and as these species diverged they all possessed this trait.
It is hypothesized that higher cognitive function evolved to mitigate the negative effects of living in social groups.
Animals that form pair bonds and share parental responsibilities produce offspring that are more likely to survive and reproduce, which increases the fitness of these individuals.
The cognitive requirements for this type of mating include the ability the differentiate individuals from their group and resolve social conflicts.
For example, the genetic mutation for color vision allowed for a greatly increased efficiency in finding and foraging fruit.
[22] Some supporters of this hypothesis suggest that higher cognitive processes require a large brain to body ratio.
For example, sea otters have been observed using a rock to break open snail shells, while primates and New Caledonian crows have demonstrated an ability to fashion a new tool for a specific use.
The researchers witnessed one female, named Imo, realize that by washing potatoes in the nearby river you could remove much more sand and dirt then by simply wiping it off.