According to the Biogenetic Law, or Recapitulation Theory, animals in their individual development pass through the stages experienced in the evolution of the race to which they belong. This scientific theory was arrived at through the study of comparative embryology and the larval stages of insects and crustacea. In the Crustacea, which includes the lobsters and crabs, certain species pass through larval stages which resemble more primitive Crustacea. Most insects undergo a change, or metamorphosis, passing from egg to larva to pupa to adult. The caterpillar changing into a butterfly is perhaps the best example of this amazing life cycle. Both Crustacea and insects molt, shedding their skins with each change, and undergoing their growth immediately before the new skin hardens.
Among the vertebrates, these different stages of growth are hidden away in the embryo, which undergoes a series of changes in its development from ovum to the time of birth, during which it recapitulates the forms of a series of lower organisms. For instance, at one stage of embryonic growth gill slits appear. In the amphibians, birds and mammals these gill slits are modified or disappear, but in the fishes they continue to the adult stage. The development of the flounder is a striking illustration of one instance where the law of recapitulation is carried on after birth. The flounder, when young, swims upright as fish commonly do, and it has an eye on each side of its head. Being a flat fish, the flounder rapidly develops the habit of turning on its side, and the eye on the then under side slowly migrates over the top of the head to join its companion on the upper side.
The Law of Recapitulation has been used by evolutionists to support the evolutionary theory, and has been advanced as evidence to prove that all life has developed from simple to complex in a long, end-on-end evolution. This is contrary to our Theosophical teachings. We say that the various stocks of life are distinct; that they do not pass one into the other, although the reimbodying monads overshadowing the organisms do so, up to a certain point after which the door is closed. To the Theosophist, recapitulation is much more important than science yet knows; it is the law of analogy; it applies to the entire life cycle, not to a mere portion of it.
As G. de Purucker states in his book, Man in Evolution:
Nature repeats herself everywhere. She follows grooves of action that have already been made; she follows the line of least resistance in all cases and everywhere, and it is upon this repetitive action of our great Mother, Universal Nature, that is founded the Theosophical doctrine of the law of cycles, which is the enacting of things which have been before.
To quote one of our great geologists, Dr. L. Snyder:
Each group of organisms has a life time — a birth, a youth, a maturity, a death — as do the individuals composing it. In fact, one of the most fundamental principles of organic evolution is the fact that each individual repeats in brief, or recapitulates, the history of the race to which it belongs.
Reproduction of the amoeba is by means of single cell division whereby the single cell becomes two individuals. At times, when the vitality is running low, instead of dying two individuals will come in contact and in some mysterious way renew their vital energy. With the amoeba, death is an accident.
In another of the protozoa, the Euglena, we find a specialized appendage for locomotion in the form of a long, slender, whip-like flagellum, which threshes about and propels the owner through the water. At the anterior end is a small, red spot which is supposed to be sensitive to light. A number of flat, circular plates are found in the body of the Euglena, which contain chlorophyll and manufacture food by photosynthesis, after the manner of a plant. However, this creature eats also after the manner of an animal, by means of a permanent food vacuole. Reproduction occurs in the Euglena by longitudinal division.
The flagellates of which Euglena is a member are a very common type of protozoa and, as might be suspected, are claimed by both zoologists and botanists.
So far, we have considered two single-celled organisms. In one — the amoeba — any part of the protoplasm is able to perform all functions. In the other, the Euglena, certain portions of the protoplasm have specialized, definite functions.
We now approach a definite step in evolution, in which we find hundreds, or thousands, of single-celled organisms living in clusters to form a hollow globe, so that each cell is in contact with the water and at the same time joined to its fellow. The best representative of this stage of development is the Volvox, a plant according to some, an animal according to others. In the Volvox each of the many cells possesses an eye spot, chlorophyll plates, a contractile vacuole and two flagella, and acts independently of its neighbor cells. Here, however, we have specialization, for certain cells increase in size and perform the function of reproduction for the colony. As yet, the association is not sufficiently dominated by the embodying entity to be classed as a many-celled organism. The association is but loosely knit together. Still, one feels that there is a foreshadowing of organization.
We have briefly examined two examples of the protozoa, and I may say in passing that 15,000 species are recognized by the zoologists, besides a host of bacteria, desmids, and microscopic algae belonging to the plant world.
I like to feel that the increasing complexity found in the plant and animal kingdom is due to the progressive descent and imbodiment of a consciousness, of a conscious entity seeking experience and a vehicle in our physical world. Slowly at first, then more and more completely, the cells submit to a purposeful if elementary will, first by uniting in colonial order (yet each cell independent of the others), then certain cells specializing, developing organs for certain functions, so that more and more we see all cell personality subordinated to organism individuality, as in greater and still greater degree the descending conscious entity becomes identified with its body, simple though that body may be.
Passing over a number of the simpler forms of life, we now pause at the hydra, a simple type abundant in both fresh and salt water, and related to the jellyfish, sea anemone, and coral. The hydra egg develops by subdivision into a hollow ball, which then infolds to form a two-celled wall about a hollow interior. The interior wall occupies about two-thirds of the body wall, and is digestive and secretory in function. Many cells possess a number of flagella, which create a current in the water, and pseudopodia or protrusions of the cell substance project and capture solid food particles swimming in the hollow stalk.
Among the cells of the hydra's outer wall, or ectoderm, are many stinging cells, which discharge a barbed thread able to paralyze any small creature or even kill it by a poison contained in the barbs. The tentacle is able to seize prey and force it into the body cavity.
Strangely, the hydra is able to move, after the fashion of a measuring worm, by bending forward, attaching itself by its tentacles, releasing its base, and advancing it for a new hold. Another method is to stand upside down and walk on its tentacles.
The hydra, by budding, often forms a colony, as is the case with our common coral.
In studying the hydra, we come to what is known as an alternation of generations, for the hydra produces not another hydra, but multitudes of small jelly-fish. These are free-swimming forms, and they lay quantities of eggs which develop into minute, free-swimming larvae. These larvae soon settle down, become fixed to the rocks and, by budding, produce a hydroid colony, thus completing a life cycle of which, unless we knew the whole story, we might well consider each stage as separate forms unrelated to one another.
In both the plant and animal kingdoms we find this alternation of forms appearing again and again.
There is a primitive land plant which I wish to mention here, the slime mold. In its early stages the slime mold resembles a small, flat mass of jelly, and moves about in dark, moist places in the woods, seeking and capturing bits of food after the manner of an amoeba. Later, it becomes fixed, erects a stalk crowned with a beautiful capsule in which spores develop.
Why, one may ask, should the early part of a plant's life be so active, and not the latter? We say it recapitulates, repeats the time when the plant kingdom was dominant, and much more active than at present.
A study of plant or animal life leads one to believe that we have a series of cycles, each repeating the same theme, yet ever on a higher order. Now one portion of the cycle is dominant, now another, as different facets of the life are brought to the fore, but over and behind all, one senses the grand rhythm of the composition.
Geologic history shows plant and animal life rising in wave after wave as the climatic cycles, large and small, come and go. Each life wave suddenly develops, reaches its climax, and declines, while at about its peak another wave appears. That which we see in the world today consists in every case of but thin streams of life, each of which once had its day in the sun, during which time it was the dominant life of the globe.
The gray, creeping club-moss under our feet once formed great forests; the scouring rush along the highway once grew a hundred feet high in Carboniferous swamps. The ancient past lives for us today in the life we so lightly consider as scarcely to notice it. The flowering plants and mammals reached their peak in numbers and variety during Miocene times, millions of years ago, and have been declining ever since.
The eucalyptus tree flourished in northern Greenland in Cretaceous times. Seven fossil species of eucalyptus have been found in Massachusetts. Native now in Australia and New Zealand, and brought to America by man's aid, what a story this tree alone could tell — what an energy of life, to last so long. A tree is not the form we see: it is a stream of life, embodying and reimbodying through untold ages.
But species grow old and die, as individuals do, and the life of a species is as the life of an individual: both pass through their childhood, maturity, and old age.
When an individual specializes it requires certain foods, special conditions to exist, or it soon ceases to survive as an embodied being. The same is as true of a species as of a race, and the strata of the geologic past are full of fossil remains of types which were unable to change with the changing environment and so passed out. These were all specializations of one kind or another, departures from the evolutionary current, or main trunk, of the stock or class.
If we study the geological history of our earth, we find long periods of warm or subtropical climate, during which the polar regions were free from ice and resembled rather a subtropical jungle. During these times a new order of plant and animal life sprang into sudden dominance, starting in the north and slowly sweeping to the southward.
At periodic times this, the normal climate of the world, was brought to a sudden end by what are quite properly called revolutions — periods of sudden cold, glaciation, and mountain buildings. At these times, all life is put to the test, and either undergoes rapid evolution or faces extinction. We are at present emerging from such a revolution, and have a new future before us.
A single cycle of this kind constitutes an era. Thus we have the Paleozoic, the age of fishes and coal forests; the Mesozoic, the age of reptiles and coniferous forests; the Cenozoic, the age of flowering plants and mammals. Within each era are a number of periods which, repeating the cycle of an era on a lesser scale, bring to the fore various lesser forms of life while retarding others.
Considering large groups of related organisms as a class or stock, and using the coniferous trees as an example, we find the earliest forms such as the monkey tree, star pine, etc., rigidly geometric in pattern, while the later pines have lost much of their design and their pollen is dependent upon wind and insects for its distribution. In the earliest representatives of the gymnosperms, the cycad and gingko, the sperm cells are motile if moisture is present, somewhat as is the case with the seaweeds.
Returning to the evergreens. The cretaceous fossil beds of northern Greenland contain the earliest types, which are later to be found in the Southern Hemisphere, while the later pines and spruces are confined to the Northern Hemisphere, forming a green belt around the earth.
We may study the Gymnosperms" life wave, which produced in turn the gingko, the monkey puzzle tree, the yew, the sequoia, the cedar, the pine, and the Ephedra or lowly desert tea, last of a great and noble line.
Consider the trees and their cousins, the shrubs and chaparral, as unfolding from a central idea, a central theme, each having its day and decline and long, slender line of surviving descendants.
Consider again the pines of the southwest — the great sugar pines and the yellow pines, tall and straight. These came to our southern mountains — the San Gabriels, the San Bernardinos, the Lagunas — during the last ice age, perhaps a million years ago, when the climate of California was similar to the climate of the Pacific Northwest today.
Then turn to the low, scrubby, brush-like, and exceedingly fragrant pinons. These pines arrived much, much earlier — during the Eocene — and have seen the San Gabriel Range worn to the level of the sea, and raised and worn again to a line of low islands, and raised again to the present levels.
Or, we might study the elephant race, as described in Professor Osborn's great work, The Proboscidians, starting with the first, a little creature two feet high, seeing the expansion in variety, in size, in specialization of trunk, tusk, and ear, seeing their decline, for all but two have now vanished from the earth. Here, again, we see the unfolding from a central focus, the expanding of a great race in great variety of form and then its contraction and near extinction.
Professor Snyder states that new forms are thrown off when a race is at its peak of vitality, and never at its close. This is true of the race, as of the individual. This, also, is true of the races of men, as explained in our Theosophical teachings.
Theosophy teaches that the current of life which is now man has been the leading force since the first formation of the ethereal earth. This current of life, moving through successive cycles of activity, has laid the pattern which all plant and animal life follow in both their individual and racial life cycles, though only the mammalian life has its origin in this Round. The other great stocks of life (birds, fishes, insects, Crustacea — all, excepting the animals and the true mammals) have arisen at different times in the far past and have only reawakened to new activity during the present life cycle of the earth, which we know as beginning with the Cambrian period.
No missing links between the larger groups have been found and none ever will be found, for there are none. For each type of life repeats after its own fashion what its predecessor did, yet it was not derived from that predecessor. Thus, to use an illustration, the fishes produced a flying fish. The reptiles produced flying, swimming, and walking species. The mammals produced the whale, the bat, and a host of land animals. Many birds are flightless; some are confined to the sea, scarcely able to waddle on land.
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