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acquired action adapted adult animals appear become behaviour body brought called cells changes characters chemical chromosomes closely colour combined comparatively complex compounds containing continuous corresponding course crossing Darwin definite depends determined Diagram differentiated directions distribution divergence division effect environment evidence evolution existence experiments fact factors factors of inheritance female fertilization forms gametes give rise groups grow heredity illustrating important increase individuals influence inheritance insects instance isolation kind known later lead less light lines living lower male material matter mean mechanism mental modifications mutation natural natural selection normal nucleus observed occur offspring organisms original parent particular pass plants possible present produced protoplasm races represented reproduction response result selection separate sexual sexual reproduction shown similar species stage steps stimulus structure struggle substance successive take place theory tion transmitted variation varieties various vary whole zygote
Page 107 - Nothing is easier than to admit in words the truth of the universal struggle for life, or more difficult — at least I have found it so — than constantly to bear this conclusion in mind. Yet unless it be thoroughly engrained in the mind, the whole economy of nature, with every fact on distribution, rarity, abundance, extinction, and variation, will be dimly seen or quite misunderstood.
Page 65 - ... same point of view has been developed by Goodrich, who stresses the distinction which has to be drawn between the process of transmission of the internal factors from parent to offspring, and the process of production in the offspring of characters similar to those which were possessed by the parent. 'An organism is moulded as the result of the interaction between the conditions or stimuli which make up its environment and the factors of inheritance. No single part is completely acquired, or...
Page 66 - Modifications are not transmitted as such. In the absence of the stimuli which originally gave rise to them they could only reappear if the new environment produced such a change in the factors of inheritance themselves that, when replaced in the old environment, they continued to respond as if the new stimuli were still present. This is what the Lamarckian theory of evolution demands. We will not say that such a thing is impossible, but it is in the highest degree improbable, and it is very difficult...
Page 89 - ... without. To say that mutations are due to the mixture or reshuffling of pre-existing factors is merely to push the problem a step farther back, for we must still account for their origin and diversity. The same objection applies to the suggestion that the complex of factors alters by the loss of certain of them. To account for the progressive change in the course of evolution of the factors of inheritance and for the building up of the complex it must be supposed that from time to time new factors...
Page 25 - the metabolic process in living matter draws in inorganic substances and force at one end, and parts with it at the other; it is inconceivable that these should, as it were, pass outside of the boundaries of the physicochemical world, out of range of the socalled physico-chemical laws, at one point to reenter them at another.
Page 64 - ... changed environment ; but, as Goodrich (1912) explains, each variety will reproduce its like .in its own locality; but seeds of an alpine plant (he has been speaking of a divided dandelion plant, one-half planted in alpine altitudes, the other half upon the lowlands — each has developed new characters) will produce only the lowland form if sown there, and vice versa; the seeds of the lowland form will grow into the alpine form in the mountains. This change is accomplished by the new growing...
Page 14 - Such is the characteristic cheerfulness in the face of hostile fact : ". . . although far from being able to give a complete scientific explanation of all the phenomena of life, we have made so much progress towards that final goal of the evolutionist that we seem fully justified in believing that the transition from the non-living to the living has indeed occurred.
Page 66 - s ' ' determinants, ' ' are all terms denoting factors, but with somewhat different meanings. More recently Professor "W. Johannsen (" Elemente der exakten Erblichkeitslehre," 1909) has proposed the term " gene " for a factor, " genotype " for the whole assemblage of factors transmitted by a species, and " phenotype " for the characters developed from them. This clear system of nomenclature, although much used in America, has not been generally adopted in this country. propagating substances, subsidiary...
Page 177 - ... imply, still less an epiphenomenon or meaningless by-product as some have held. I am well aware that the view just put forward is rejected by many philosophers, nevertheless it seems to me to be the best and indeed the only working hypothesis the biologist can use in the present state of knowledge. The student of biology, however, is not concerned with the building up of systems of philosophy, though he should realize that the mental series of events lies outside the sphere of natural science.
Page 99 - ... factors of inheritance exist, and the fundamental problem of Biology is, how are the factors of an organism changed, or how does it acquire new factors? In spite of its vast importance, it must be confessed that little advance has been made towards the solution of this problem since the time of Darwin, who considered that variation must ultimately be due to the action of the environment This conclusion is inevitable, since any closed system will reach a state of equilibrium and continue unchanged,...