And false, 6x mass does NOT mean 6 times gravity.
The radius is indeed proportional to the cube root of the mass so if r = r_earth * M^(1/3). Then, g will be g_earth * M / (M^(1/3))^2 = g_earth*M^(1/3) and everyone will be 1.91 times heavier.
You might be able to walk for a little bit before... ROFL
"Before fainting, he mentions yawning and feeling "sleepy and cold". Chronic hypergravity tests on rats, mice, dogs and monkeys (between 1.25g and 2.5g) have shown an effect on circadian rhythms: decreased locomotor activity (perhaps indicating drowsiness) and a drop in core body temperature, a "centrifuge-induced hypothermic response"."
http://jap.physiology.org/content/95/3/1266.full
But lifeforms very well could have evolved to what we would know as extra gravity.