M Database Inspector (cheetah)
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|OriginOfSpecies - 475 Rows|
|02 - Variations Under Nature||02-04 - Wide-ranging, much diffused, and common Species vary most||30||
With respect to the number of individuals or commonness of species, the comparison of course relates only to the members of the same group.
One of the higher plants may be said to be dominant if it be more numerous in individuals and more widely diffused than the other plants of the same country, which live under nearly the same conditions.
A plant of this kind is not the less dominant because some conferva inhabiting the water or some parasitic fungus is infinitely more numerous in individuals and more widely diffused.
But if the conferva or parasitic fungus exceeds its allies in the above respects, it will then be dominant within its own class.
|07 - Instinct||07-03 - Aphides and ants||30||
as in the case of corporeal structure, and conformably with my theory, the instinct of each species is good for itself, but has never, as far as we can judge, been produced for the exclusive good of others.
One of the strongest instances of an animal apparently performing an action for the sole good of another, with which I am acquainted, is that of aphides voluntarily yielding their sweet excretion to ants: that they do so voluntarily, the following facts show.
I removed all the ants from a group of about a dozen aphides on a dock-plant, and prevented their attendance during several hours.
After this interval, I felt sure that the aphides would want to excrete.
I watched them for some time through a lens, but not one excreted; I then tickled and stroked them with a hair in the same manner, as well as I could, as the ants do with their antennae; but not one excreted.
Afterwards I allowed an ant to visit them, and it immediately seemed, by its eager way of running about, to be well aware what a rich flock it had discovered; it then began to play with its antennae on the abdomen first of one aphis and then of another; and each aphis, as soon as it felt the antennae, immediately lifted up its abdomen and excreted a limpid drop of sweet juice, which was eagerly devoured by the ant.
Even the quite young aphides behaved in this manner, showing that the action was instinctive, and not the result of experience.
But as the excretion is extremely viscid, it is probably a convenience to the aphides to have it removed; and therefore probably the aphides do not instinctively excrete for the sole good of the ants.
Although I do not believe that any animal in the world performs an action for the exclusive good of another of a distinct species, yet each species tries to take advantage of the instincts of others, as each takes advantage of the weaker bodily structure of others.
So again, in some few cases, certain instincts cannot be considered as absolutely perfect; but as details on this and other such points are not indispensable, they may be here passed over.
|14 - Recapitulation and Conclusion||14-05 - Effects of its adoption on the study of Natural history||30||
A new variety raised by man will be a far more important and interesting subject for study than one more species added to the infinitude of already recorded species.
Our classifications will come to be, as far as they can be so made, genealogies; and will then truly give what may be called the plan of creation.
The rules for classifying will no doubt become simpler when we have a definite object in view.
We possess no pedigrees or armorial bearings; and we have to discover and trace the many diverging lines of descent in our natural genealogies, by characters of any kind which have long been inherited.
Rudimentary organs will speak infallibly with respect to the nature of long-lost structures.
Species and groups of species, which are called aberrant, and which may fancifully be called living fossils, will aid us in forming a picture of the ancient forms of life.
|12 - Geographical Distribution -- continued||12-40 - On the relations of the inhabitants of islands to those of the nearest mainland||30||
All the foregoing remarks on the inhabitants of oceanic islands, namely, the scarcity of kinds -- the richness in endemic forms in particular classes or sections of classes, the absence of whole groups, as of batrachians, and of terrestrial mammals notwithstanding the presence of aerial bats, the singular proportions of certain orders of plants, herbaceous forms having been developed into trees, &c., seem to me to accord better with the view of occasional means of transport having been largely efficient in the long course of time, than with the view of all our oceanic islands having been formerly connected by continuous land with the nearest continent; for on this latter view the migration would probably have been more complete; and if modification be admitted, all the forms of life would have been more equally modified, in accordance with the paramount importance of the relation of organism to organism.
I do not deny that there are many and grave difficulties in understanding how several of the inhabitants of the more remote islands, whether still retaining the same specific form or modified since their arrival, could have reached their present homes.
But the probability of many islands having existed as halting-places, of which not a wreck now remains, must not be overlooked.
I will here give a single instance of one of the cases of difficulty.
Almost all oceanic islands, even the most isolated and smallest, are inhabited by land-shells, generally by endemic species, but sometimes by species found elsewhere.
Dr. Aug. A. Gould has given several interesting cases in regard to the land-shells of the islands of the Pacific.
Now it is notorious that land-shells are very easily killed by salt; their eggs, at least such as I have tried, sink in sea-water and are killed by it.
Yet there must be, on my view, some unknown, but highly efficient means for their transportal.
Would the just-hatched young occasionally crawl on and adhere to the feet of birds roosting on the ground, and thus get transported? It occurred to me that land-shells, when hybernating and having a membranous diaphragm over the mouth of the shell, might be floated in chinks of drifted timber across moderately wide arms of the sea.
And I found that several species did in this state withstand uninjured an immersion in sea-water during seven days: one of these shells was the Helix pomatia, and after it had again hybernated I put it in sea-water for twenty days, and it perfectly recovered.
As this species has a thick calcareous operculum, I removed it, and when it had formed a new membranous one, I immersed it for fourteen days in sea-water, and it recovered and crawled away: but more experiments are wanted on this head.