Vietnam or Thailand ? Vote for the TOP Country of the Week !
Updated: May 4, 2025
Variability in the same parts of the organisation has generally been taken advantage of in giving secondary sexual differences to the sexes of the same species, and specific differences to the several species of the same genus.
It may be possible that the lack of horns makes it more difficult to break a zebra's neck because of the corresponding lack of leverage when its head hits the ground sidewise; the instances I have noted may have been those in which the lion's spring landed too far back to throw the victim properly; or perhaps they were merely examples of the great variability in the habits of felis leo.
This greater variability in mongrels than in hybrids does not seem at all surprising. The slight variability of hybrids in the first generation, in contrast with that in the succeeding generations, is a curious fact and deserves attention.
But the variability, which we almost universally meet with in our domestic productions is not directly produced, as Hooker and Asa Gray have well remarked, by man; he can neither originate varieties nor prevent their occurrence; he can only preserve and accumulate such as do occur.
A high degree of variability is obviously favourable, as freely giving the materials for selection to work on; not that mere individual differences are not amply sufficient, with extreme care, to allow of the accumulation of a large amount of modification in almost any desired direction.
We see, also, that any important change in treatment and surroundings, if not sufficient to kill, would and does tend to produce not only variability but sterility, as part of the same story and for the same reason namely, default of memory; this default will be of every degree of intensity, from total failure, to a slight disturbance of memory as affecting some one particular organ only; that is to say, from total sterility, to a slight variation in an unimportant part.
Thus, comets whose fires are formed of different materials, each take and preserve a color which is peculiar to them." Instead of being a cause of fear and terror, the variety and variability of the aspect of comets ought rather to indicate to us the harmlessness of their nature. The track of the eclipse lay south of the equator, but north of Tahiti.
In the long run selection gains the day, and we do not expect to fail so far as to breed a bird as coarse as a common tumbler from a good short-faced strain. But as long as selection is rapidly going on, there may always be expected to be much variability in the structure undergoing modification.
I cannot make out that it applies to plants, and this would seriously have shaken my belief in its truth, had not the great variability in plants made it particularly difficult to compare their relative degrees of variability.
Thousands of seeds with perhaps wide circles of variability are ripened each year, but only those that belong to the existing old narrow circles survive. How different would Nature appear to us if she were free to evolve all her potentialities! Darwin himself was struck with this lack of harmony between common observations and the probable real state of things.
Word Of The Day
Others Looking