The brain's four lobes are the frontal lobe, temporal lobe, parietal lobe, and occipital lobe. Each lobe exists in a distinct part of the cerebral cortex and serves a different primary function. The frontal lobe is located toward the front of the brain, directlly behind the forehead, and is used to process higher level thinking such as conscious thought. The temporal lobe is located toward the outside of the head, behind the temple and ears, and is responsible for auditory processing. The parietal lobe is located superior to (above) the temporal lobe at the top of the head and is primarily responsible for processing motor and sensory functions. The occipital lobe is located at the back of the head and processes visual signals.

The corpus callosum is a thick band of nerve fibers that connects the left and right hemispheres of the cerebal cortex. Its main purpose is to facilitate communication between the two hemispheres.

The precentral gyrus and central sulcus are topical features of the brain (a ridge and a groove, respectively) that separate the frontal and parietal lobes.

The cerebellum, located in the rear of the brainstem, helps coordinate our voluntary movements and helps us maintain balance.

The medulla oblongata controls our breathing and heart rate. It is located at the base of the brainstem. Note that most structures in the brainstem are associated with essential, involuntary functions.

The frontal lobe, specifically the prefrontal cortex, is involved in complex decision-making and making goal-oriented plans. 

Natural selection is the theory that certain traits become more or less common in a population based on its reproductive success in a group of organisms. Evolutionary (sometimes called Darwinian) psychology studies human thought in the context of Darwinian evolution.

Chromosomes are complex structures that contain a molecule of DNA and a protein. DNA strands contain genetic information. 

Darwin's principle of natural selection holds that the genes most likely to increase the chance of survival and reproduction are also the most likely to be passed on. Survival and reproduction are the fundamental basis of Darwin's principles.

There are many dimensions that make the human species united as well as many that differentiate humans from one another One factor that unites humans is the imperative to use language, a trait that has evolved over time to help us communicate and coexist with one another. Other common factors among humans are biological heritage, brain architecture, and social behavior. The ability to eat dairy products and experience empathy are not common to all people, as some people are lactose intolerant, and some are psychopathic, and largely incapable of empathy and sympathy. While a nurturing instinct is extremely common, it is not considered a universally common human trait.

The human species is united on many fronts, namely our social bonding tendencies, inherited mental structures, biological origins, and the predisposition to acquire language. Of course there are exceptions to this, as a variety of disorders may affect our abilities to acquire language, bond socially, or the development of our cognitive functions. These traits are, however, widely observable in the majority of the human species.

The dimensions that make most of us different from one another, both at the individual and societal level, have to do with our personalities, familial upbringing, cultures, and personal interests.