Well scientifically speaking probably the Extrovert. Introversion is more linked with blood flow towards our neo cortex.
Edit- Copied from wiki
One study found that introverts have more blood flow in the frontal lobes of their brain and the anterior or frontal thalamus, which are areas dealing with internal processing, such as planning and problem solving. Extraverts have more blood flow in the anterior cingulate gyrus, temporal lobes, and posterior thalamus, which are involved in sensory and emotional experience.[SUP][/SUP] This study and other research indicates that introversion-extraversion is related to individual differences in brain function.
Extraversion has also been linked to physiological factors such as respiration, through its association with surgency
There was no first extrovert or introvert human. We descended from our ancestors, who were populations of animals that bred over many generations. Let's go back in the ancestor timeline millions of years, before the archaic Homo Sapien, the Neandertal, the Homo Erectus, Snookie, and so on. Along this journey (like 280 millions years back), way before the hominids, our ancestors would seem very strange to us, very fish-like indeed.
This makes me wonder.... Do animals other than humans have introverted and extroverted tendencies? I've seen a few studies on the lifespan of gorillas/bonobos in relation to extroversion. Maybe there were hominids, too, who chilled back in the cave and munched on some berries, while the grunting wild-haired leader looked for meat. I'm sure that both the I-and-E have their values in the animal kingdom.