To define the term Alpha Male in human terms we need an understanding of both behavioral and biological Science.
Over the past 100 years anthropologists, sociologists and psychologists have studied the nature of socialization in animals, primates and Man and concluded that we are following a pattern that has evolved from hundreds of millions of years of successful adaptations. Animals of many species tend to form small groups of 5-20 individuals. This small group, socialization or culture is referred to as the "Tribal Model" and is found throughout the animal kingdom. The survival of many species is inextricably linked to the functioning of these social groups.
During the 1930's the mechanisms of genetics were discovered and explored, and over the past 20 years, Medical science has begun to develop an accurate idea of the mechanics and details of the electro-chemical functions of the brain itself. Research in these fields has advanced our understanding of how we think and react emotionally and why we behave the way we do.
As amazing as the cognitive functions of the human brain are, it is not Reasoning, Organization, Analysis, or Memory, that are responsible for Happiness. The joy of being alive, Self-awareness, Pleasure, and Pain, Contentment, Belonging, in fact, nearly all the emotional content of life originates and is experienced within a group of organs and nerves called the Limbic System. These primitive, structures have existed for millions of years in vertebrate animals and have no memory or cognitive ability. This "Old Brain" is reactive, emotional, and intuitive. It lies between the raw senses and the cognitive, thinking brain. The Limbic systen attaches emotional urgency to any stimulus and thus controls attention. It serves to filter, sort, and evaluate the information streaming into the nervous system from the senses before they even reach the thinking part of the brain, the Neo-cortex "NEW BRAIN."
One major obstacle to peace, comfort and happiness that all social animals face, is weak leadership. The majority of the members of any socialized species will seek and bond to a strong leader to assure their survival. There are only a small percentage of individuals born with the natural qualities of leadership, intellect and strength that convey an advantage to any group.
These natural born leaders, especially in primates, are almost always male, and are referred to as the "Dominant" or "Alpha" male. The "Alpha" male has evolved for millions of generations and the genetic adaptations are quite profound. The Human Alpha Male evolved from these early animal and "Hominid" ancesters. He is gifted with many adaptations that predispose Him to leaderhip. He is usually, large, strong, intelligent, attractive, and possesses a charismatic ability to generate trust, foster calm, and promote cooperation within His group. Quite often He has a similar but less profound effect on others outside His immediate sphere of influence.
Recent studies have shown that even at the level of basic brain function there are differences between Alpha and other Males. A true Alpha shows significantly higher levels of a critical brain chemical, Serotonin. A precurser to several polypeptide neurotransmitters, Serotonin is secreted within the limbic system at elevated levels when He has responsibilities and is actively Dominant.
Another Male will ascend to the dominant role in the absence of a true genetic Alpha, but his serotonin level will not rise to reflect his position within the group, and should a genetic, Alpha arrive upon the scene, He will quickly recognize Him and relinquish the leaders role.
A true Alpha Male is rarely challenged by any other male even while he is young and weak, and females recognize Him as an ideal mate. He is often quite gentle, within his group, but will rise to their defense with vigor and ferocity, when the group is threatened.
The desire to locate and mate with such a Man is at the heart of much Male Dom/fem sub behavior. The female senses she will find safety, comfort, excitement, and emotional fulfillment, with an Alpha, and she finds Him very compelling. Most females will readily display the signs of submission and willingness to mate even before reaching sexual maturity.
These non-verbal signals are recognised and understood, instinctively, by modern humans and exist in the common flirting gestures and postures that can be seen in any social setting where there is interaction between the sexes.