Among the forms of life we perceive on this Earth, humanity is gifted with exceptional mental powers. Specifically, our power of thought - the ability to negotiate possible futures through the abstract vehicle of symbols (words, pictures, formulas, etc.) - has made us masters of this kingdom.
Why is thought important? Let's consider evolutionary theory.
Darwin was not the only proponent of evolution. Lamarck also offered a theory that proposed competition as the driving force of species development. Darwin noticed, however, that in the animal kingdom at large, individual improvements were transmitted only through procreation. If an animal developed improvements during its life - for example, larger muscles due to exertion - these could not be transferred to its progeny.
Lamarck had the opposite philosophy. He held that an herbivore feasting on leaves, if forced to stretch its neck because overpopulation caused depletion of leaves on lower branches, would pass the predisposition for a longer neck on to its progeny. Lamarck preferred this hypothesis because it meant that species could evolve far more rapidly. Rather than only at the moment of conception, every moment of contact between an adult and a child was an opportunity to transmit the benefits of experience.
Darwin, of course, has been preferred. Lamarck was rejected because he appeared to subscribe to magical thinking: he could not specify a mechanism for transmittal of characteristics developed during life to an animal's offspring. Darwin, on the other hand, had the work of Mendel with peas, which showed that plant characteristics where transmitted through seeds. Today, we know that the specific mechanism of transmittal is DNA (deoxyribonucleic acid).
Unfortunately, in one specific realm, Darwin's ideas have been misapplied. Social competition is engaged almost entirely in the domain of thought. The capacities present in a baby when it leaves the womb are completely unsatisfactory for his survival in the world of adults. Obviously, improved motor skills and physical strength are critical to survival in an adult world, and the limits of those capacities are defined genetically. In the modern world, however, machinery reduces the significance of those differences. Far more important are the social and productive thought processes originating from his elders. To the degree that his teachers have improved the skills passed on to them from their predecessors, the child will also benefit.
Human beings, to a degree unique among living creatures, benefit from Lamarckian evolution. (Bacteria, which exchange DNA plasmids, may also be thought of as participants in Lamarckian evolution. However, this method is not significantly more efficient than normal genetics.) The manifestation of thought means that we adapt to our environment far faster than other species. Furthermore, we are capable, through thought, of conceiving of and constructing man-made environments, to the degree that we have succeeded in redefining the nature of existence in almost every corner of our world.