The cells and fibers of the brain must carry some kind of individual identification tags, presumably cytochemical in nature, by which they are distinguished one from another almost, in many regions, to the level of the single neurons.

Where people worry is when you get to the brain, the germ cells and the sentinel features that help people recognize what is a person, as opposed to a rat or a rabbit. Things like skin texture, facial shape, speech, replacing brain cells with human cells, allowing the development of human germ cells in animals. And particularly where there is any possibility of fertilisation within an animal.

The scientific basis for separating neocortical from limbic brain matter rests on solid neuroanatomical, cellular, and empirical grounds. As viewed through the microscope, limbic areas exhibit a far more primitive cellular organization than their neocortical counterparts. Certain radiographic dyes selectively stain limbic structures, thus painting the molecular dissimilarity between the two brains in clean, vivid strokes. One researcher made an antibody that binds to cells of the hippocampus — a limbic component — and found that those same fluorescent markers stuck to all parts of the limbic brain, lighting it up like a biological Christmas tree, without coloring the neocortex at all. Large doses of some medications destroy limbic tissue while leaving the neocortex unscathed, a sharp-shooting feat enabled by evolutionary divergence in the chemical composition of limbic and neocortical cell membranes.

The linear size of a neuron varies widely from one nerve cell to the other, since some of these cells are contained in closely integrated large aggregates and have, therefore, very short axons, while others conduct pulses between rather remote parts of the body and may, therefore, have linear extensions comparable to those of the entire human body.

We are no more alike under the skin than we are on top of it.

some types of neurons may be found only in specific species.

There are approximately two billion cells in the nervous system of a human being. The process of thinking in any individual is partly dependent upon the variable arrangement of these cells. Therefore no person can think exactly as another, any more than he can change his facial features to duplicate the facial features of another. If people would remember this fact and regulate their attitudes towards others to conform to it, it would encourage the exercise of tolerance, the human attribute most needed today.

Cell differentiation can turn neurons into everything from clocks that control circadian rhythms to photoreceptors that convert light into electrical-chemical impulses or decision makers that tally votes and decide courses of action. In the retina (often used as a case study because it can be directly and naturally stimulated), there are at least fifty different kinds of neurons specialized to different tasks, such as looking for motion, recognizing colors, detecting objects in low light, and measuring brightness and contrast. In the brain as a whole, there may be as many as 10,000 different kinds of neurons, each contributing to a different aspect of mental life.

The firing of individual nerve cells involved in perceptual and motor processing is modified by attention and decision making.

By differentiation we mean the differences in cognitive and emotional orientation among managers in different units and the differences in formal structure among units.

For decades, biology has been dominated by information—the power of genes. ...[Y]et there is no difference in the information content of a living protozoon and one that died ...The difference between alive and dead lies in energy flow ...the ability of cells to continually regenerate themselves from simpler building blocks.

Perhaps you think that the crucial difference between a fly and a human blastocyst is to be found in the latter's potential to become a fully developed human being. But almost every cell in your body is a potential human being, given our recent advances in genetic engineering. Every time you scratch your nose, you have committed a Holocaust of potential human beings. This is a fact. The argument from a cell's potential gets you absolutely nowhere.

Minds differ still more than faces.

It is the story that owns and directs us. It is the thing that makes us different from cattle; it is the mark on the face that sets one people apart from their neighbors.