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Different types of cells have different lifespans, e.g.: we shed our skin cells about every 35 days red blood cells live about 120 days, platelets 6 days and white cells less than a day most of the adult skeleton is replaced about every 10 years the average age of a fat cell seems to be about 10 years a 25-year-old…
Many species of terrestrial plants, including the skunk cabbage that sprouts in February in the woods of Princeton, New Jersey, where I live, are warm-blooded to a limited extent. For about two weeks the skunk cabbage maintains a warm temperature by rapidly metabolizing starch stored inside the part of its anatomy…
Careful and reproducible observations and measurements in the bbiosciences have similarly forced us to repeatedly refine our traditional ideas about what life itself is and when it begins. Is a human being first a life when it emerges from the birth canal? Does it have any legal rights is as a person before then? Or…
It is an old saying, abundantly justified, that where sciences meet there growth occurs. It is true moreover to say that in scientific borderlands not only are facts gathered that [are] often new in kind, but it is in these regions that wholly new concepts arise. It is my own faith that just as the older biology from…
Muscles are in a most intimate and peculiar sense the organs of the will. They have built all the roads, cities and machines in the world, written all the books, spoken all the words, and, in fact done everything that man has accomplished with matter. Character might be a sense defined as a plexus of motor habits.
We know that nature invariably uses the same materials in its operations. Its ingeniousness is displayed only in the variation of form. Indeed, as if nature had voluntarily confined itself to using only a few basic units, we observe that it generally causes the same elements to reappear, in the same number, in the…
It will be noticed that the fundamental theorem proved above bears some remarkable resemblances to the second law of thermodynamics. Both are properties of populations, or aggregates, true irrespective of the nature of the units which compose them; both are statistical laws; each requires the constant increase of a…
A vital phenomenon can only be regarded as explained if it has been proven that it appears as the result of the material components of living organisms interacting according to the laws which those same components follow in their interactions outside of living systems.
A man in twenty-four hours converts as much as seven ounces of carbon into carbonic acid; a milch cow will convert seventy ounces, and a horse seventy-nine ounces, solely by the act of respiration. That is, the horse in twenty-four hours burns seventy-nine ounces of charcoal, or carbon, in his organs of respiration to…
What we call man is a mechanism made up of … uncrystallized matter … all the colloid matter of his mechanism is concentrated in a countless number of small cells. … [T]hese cells [are] dwelling places, communes, a walled town within which are many citizens. ... [T]hese are the units of life and when they pass out into…
Each nerve cell receives connections from other nerve cells at six sites called synapses. But here is an astonishing fact—there are about one million billion connections in the cortical sheet. If you were to count them, one connection (or synapse) per second, you would finish counting some thirty-two million years…
A living organism must be studied from two distinct aspects. One of these is the causal-analytic aspect which is so fruitfully applicable to ontogeny. The other is the historical descriptive aspect which is unravelling lines of phylogeny with ever-increasing precision. Each of these aspects may make suggestions…
From thus meditating on the great similarity of the structure of the warm-blooded animals, and at the same time of the great changes they undergo both before and after their nativity; and by considering in how minute a portion of time many of the changes of animals above described have been produced; would it be too…
From the time of Aristotle it had been said that man is a social animal: that human beings naturally form communities. I couldn't accept it. The whole of history and pre-history is against it. The two dreadful world wars we have recently been through, and the gearing of our entire economy today for defensive war belie…
A large proportion of mankind, like pigeons and partridges, on reaching maturity, having passed through a period of playfulness or promiscuity, establish what they hope and expect will be a permanent and fertile mating relationship. This we call marriage.
We are now witnessing, after the slow fermentation of fifty years, a concentration of technical power aimed at the essential determinants of heredity, development and disease. This concentration is made possible by the common function of nucleic acids as the molecular midwife of all reproductive particles. Indeed it…
I took biology in high school and didn't like it at all. It was focused on memorization. ... I didn't appreciate that biology also had principles and logic ... [rather than dealing with a] messy thing called life. It just wasn't organized, and I wanted to stick with the nice pristine sciences of chemistry and physics…
If we examine the accomplishments of man in his most advanced endeavors, in theory and in practice, we find that the cell has done all this long before him, with greater resourcefulness and much greater efficiency.
I came to biochemistry through chemistry; I came to chemistry, partly by the labyrinthine routes that I have related, and partly through the youthful romantic notion that the natural sciences had something to do with nature. What I liked about chemistry was its clarity surrounded by darkness; what attracted me, slowly…
There is a strange disparity between the sciences of inert matter and those of life. Astronomy, mechanics, and physics are based on concepts which can be expressed, tersely and elegantly, in mathematical language. They have built up a universe as harmonious as the monuments of ancient Greece. They weave about it a…