Co-adaptation

Abstract

THE remarks on this subject made by Dr. Romanes (NATURE, March 26, p. 489) do not appear to me to present the case in a fair light, and I therefore think it advisable to make some further observations. In the first place, I do not allow that there is any “fortuity” in the supposition that certain variations, A, B, C, D, &c, may arise in the same individual, for every variation, of whatever kind, must of necessity entail numerous structural and functional modifications. If variations in the length of neck or leg or wing, in the strength of certain muscles, or even in colour, arise “fortuitously” (meaning thereby through some unknown cause antecedent to birth), there must be corresponding variations in the length of the bones, nerves, blood-vessels, &c, as well as in the physiological processes upon which depends the supply of nutriment to the parts in question. If any variation survives, or is perpetuated by breeding, it must therefore possess not only the external visible character A, but also all the concomitant and less obvious or altogether undiscoverable modifications, B, C, D, &c. However complex the correlated modifications may be, the mere existence of the variation implies the existence of such modifications, and the survival of the variation implies the survival of these correlated modifications. If, therefore, it is argued that any variation is a simple case of modification in some one character only—as might be inferred from Dr. Romanes's letter—this is an unwarranted assumption entirely opposed to fact.