But it is also hard to suppose that in any actual case is the matter so simple as it appears to our limited comprehension. To take for instance the above example of the giraffe. It is very well to have a neck that will reach high-branches of a tree,--but this is not everything. For the mere prolongation of life, much else is required, fleet limbs to distance lions, and keen senses, sight, hearing, and smell, to give warning of the approach of human or other hunters, to say nothing of the extra strengthening of muscles and bones which increased size and weight demands. Unless, however, improvements in all these respects happened casually to concur in the same individual, which could scarcely happen, it is clear that each would militate against the others, for the survival of an individual beneficially developed in one respect, would tend to the extinction of other beneficial developments, possessed by individuals whom he overcame in the struggle for life. Even the case of the insular insects is by no means so plain as might at first sight appear. There can be no doubt that wings are of _some_ advantage, or on no system could they be supposed to exist. Nor do their advantages cease because disadvantages outweigh them. If some insects are blown out to sea when flying, others will doubtless perish in one way or another because they cannot fly. It may even be that those which can fly _best_ will survive, as being able to make head against a breeze which overpowers others. Natural Selection will thus have many arrows in its quiver, some of which must reach the wrong objects. Still more clearly does this appear in the case of complex structures in which, if they were produced as Mr. Darwin supposes, variation must have hit simultaneously upon independent contrivances, without each of which all the others would be useless and confer no benefit at all. In the eye, for example, to mention but one or two of innumerable similar points, it would be of no avail to have a retina, even such as has been described, without a lens to throw an image upon it, set just at the proper distance, and provided with muscles to alter its shape according to the distance of the object. How can Natural Selection be even conceived to have set to work on such a task as this?