Reptile Activity 
195 
increases the cost of living. Endothermy 
combined with active foraging habits in a 
group with a complete double pump would 
be one powerful set of conditions favoring 
evolutionary “advances” in anatomy and be- 
havior. Hence, it could have been that en- 
dothermy accelerated the (often parallel) 
evolution of the various neurological, loco- 
motory, and masticatory specializations as- 
sociated with “intelligence,” agility, and 
speed in various mammalian groups. 
Selection pressures for endothermy based 
on a high resting metabolic rate may have 
been most intense in small animals. The 
thermal inertia of large bodies damps out 
temperature fluctuations and also facilitates 
the retention of heat generated in muscular 
activity. This recycling of the heat of ac- 
tivity (as in insects and likely also in the 
leatherback turtle) can provide a degree of 
independence from thermal fluctuation dur- 
ing activity to reduce the selection pressures 
for an increase in resting metabolic rate 
among large animals. This line of thought 
suggests that large mammals have a high 
resting metabolic rate primarily because this 
became flxed in the physiology of their small 
ancestors. Also, minimizing selection for a 
great increase in the basal metabolic rate of 
animals approaching the size of giant dino- 
saurs is that high metabolism could com- 
pound heat overloading problems because the 
low surface to mass ratios may present a 
difficulty in dumping heat. 
FORAGING MENTALITIES AND 
BRAIN EVOLUTION 
What differences might we expect in 
mental functions between active foragers 
and sit-and-wait predator lizards ? This ques- 
tion is of interest for understanding factors 
leading to diversification of lizards’ brains, 
and its answer may also give insight into the 
evolution of the mammalian nervous system 
inasmuch as a typical mammal is a more 
active forager than a typical reptile. 
Since large brains are found in warm- 
blooded birds and mammals, some are 
tempted to assume that such nervous sys- 
tems are somehow dependent upon endo- 
thermy (e.g.. Young, 1962). Jerison (1973) 
has argued, rather, that the relationship was 
caused by separate factors in the history 
of each group: flight in birds, and noctur- 
nality in mammals. Heath (1968) argued 
that mammalian brain specializations may 
have begun in response to the locomotor 
shifts from a sprawling to an erect gait. I 
suggest that development of a four-cham- 
bered heart allowed extreme specialization 
in active foraging and that, for this way of 
food gathering, there are great selective ad- 
vantages to be derived from the development 
of enlarged memory capacities and enlarged 
and advanced information-processing capaci- 
ties and systems, especially for terrestrial 
animals. Endothermy is simply another 
adaptation for this same way of life and is 
related to brain enlargement only because, 
once it became established in the physiology 
of any species, for reasons discussed above, 
endothermy would lock individuals into high 
food requirements and hence bias future 
evolution toward progressively refined ac- 
tive forager adaptations, including behaviors 
and mental capacities. Sitting and waiting 
may be expensive (in terms of time wasted) 
for many mammals with their high energetic 
demands. 
Some Operational Assumptions 
Brain Size and “Intelligence” 
There is general agreement that large- 
brained vertebrates are more “intelligent” 
than those with smaller brains, yet the spe- 
cific adaptive significance of brain size has 
not yet been identified (Holloway, 1974; 
Jerison et. al., 1975; Miller and Tallarico, 
1974; Radinsky, 1975). To avoid speculating 
on the significance of brain size or on the 
meaning of “intelligence,” I propose a set 
of deductions about specific mental qualities 
which may be useful in generating verifiable 
predictions about the adaptive functions, 
