Valerie Stone
Cognitive & Social Neuroscience
Valerie Stone
Cognitive & Social Neuroscience
The Frontal Lobes & Brain Evolution
"Humans are remarkable among primates for our large brains and complex cognitive skills. Evolutionary approaches to
cognitive neuroscience should explain how humans came to have these unique features. The challenge for evolutionary
cognitive neuroscience is weaving together available information from comparative neuroscience, archaeology,
evolutionary psychology and cognitive neuroscience in a way that illuminates human cognition. Uniquely human
cognition includes recursion, episodic memory/future planning, executive function, language with complex syntax,
and execution of complex action sequences – abilities that depend on the “executive brain” (neocortex + striatum),
particularly frontal and temporal lobes. Both extent of childhood/adolescence and brain size have increased in hominid
evolution. In primates, childhood/adolescence includes specific changes in cortical neuroanatomy: late synaptic growth
and pruning in frontal and temporal lobes, which may take longer for larger brains. This chapter presents evidence
for three key points. 1) In 30 primate species, extent of childhood/adolescence is strongly related to executive
brain size (r-squared=0.90). Extension of childhood/adolescence may have been an important genetic change underlying
hominid brain expansion. 2) Human data lies almost exactly on the regression line for nonhuman primates relating
brain size and development, as does estimated extinct hominid data. 3) Preliminary analyses on 6 species indicate
that extent of childhood/adolescence is most strongly related to size of lateral prefrontal and temporal cortex, which
handle many of our unique abilities. Longer childhood/adolescence in hominids allowed more time for neural development
in these areas. Regression analyses on comparative data are an important source of inferences about
hominid brain evolution." Abstract of Stone, V.E. (2007). The evolution of ontogeny and human
cognitive uniqueness: Selection for extended brain development in the hominid line. In S.M. Platek, J.P. Keenan,
T.K. Shackelford, Eds. Evolutionary Cognitive Neuroscience, MIT Press.
"Western culture has a long history of placing "man" above "beast" and emphasizing the huge gap between our species and
all others, particularly when it comes to our mental capacities. Many people believe we are civilized and refined in our
social behavior, certainly not like our screeching, teeth-baring cousins, the other primates....However, humans are
animals. In particular, we are social animals, adapted to living in groups.... Many of our social behaviors are shared
with our primate cousins, thus so must be many of our social cognitive abilities. However, there are clearly some aspects
of our social cognition that are unique to our species.
.... A key question ... is to what extent brain systems that subserve social behavior are domain-specific, consisting of
neural processes that operate preferentially on social information, and to what extent they are domain-general, and rely
on the same neural processes that subserve multiple areas of cognition....Domain-specific cognitive systems are adaptations,
mechanisms specialized for particular functions and designed by natural selection over millions of generations to have
information-processing features specific to the cognitive problem being solved (Cosmides & Tooby, 1987).... Because
adaptations are so complex, each design feature must evolve layered onto previous features; special design in an
adaptation thus takes a long evolutionary time to emerge (Williams, 1966; Dawkins, 1987). Much of our emotional life,
our social motivations and social intelligence are doubtless shared in common with other primates and mammals who faced
the same adaptive problems. There have been tens or hundreds of millions of years to refine neural adaptations for those
domains of behavior.
Abilities that are recent and unique to the hominid line, however, are not likely to depend solely on domain-specific
systems.... Thus, to understand social intelligence, we must look at how domain-specific systems that we share with other
primates interact with more general cognitive abilities that are uniquely human....Our capacity for executive function,
for embedding and recursion, and for metarepresentation enable not only our complex social cognition, but many of our
other uniquely human abilities as well: symbolic language, syntax, future planning, episodic memory, and tool use just
to name a few (Suddendorf, 1999; Corballis, 2003; Stone & Gerrans, 2006) Yet these domain-general abilities would have
no usefulness in the social world if they could not operate using the output of several more ancient domain-specific
social abilities." The frontal lobes are ideally situated, in connectivity, to combine the output of several
domain-specific computations.
.... Over the past 6-7 millions years, the frontal and temporal lobes were increasing in size and developmental
complexity (Semendeferi et al., 2001; Lieberman et al., 2002; Stone, 2007). Uniquely human aspects of language, for
example, depend on recursion (Hauser et al., 2002; Corballis, 2003), and such complex syntactic abilities seem to
involve areas in left temporal-parietal cortex and inferior frontal regions (Cooke et al., 2001; Caplan et al., 2002).
Executive function involves lateral prefrontal cortex. Thus, these brain regions may be the seat of the domain-general
abilities that are the hallmark of Homo sapiens sapiens." Excerpted from
Stone, V.E. (in press). An evolutionary perspective on domain-specificity in social intelligence.
In P. Winkielman & E. Harmon-Jones, Eds. Social Cognitive Neuroscience, Guilford Press.