satisfactorily explains the method in which species have been produced by evolution from other previously existing forms. No naturalist at the present day, it may safely be said, doubts that the theory of the origin of species by means of natural selection is true so far as it goes, and that it satisfactorily explains the principal difficulties which it can be legitimately called upon to explain. 'Natural Selection' is, in other words, universally recognised as a vera causa. The chief point that can be said now to be at issue among naturalists is not whether it be a genuinely active cause, but only as to the extent to which it can be applied-some regarding it as the sole factor in the production of 'species,' while others look upon it as being only one of many concurrent factors.

Darwin's life need only be referred to here in the briefest way, and only for the purpose of showing how thoroughly it qualified him for the task of elaborating and establishing his great theory. Charles Darwin was born at Shrewsbury, on the 12th of February 1809. His father was Dr Robert Waring Darwin, a physician of Shrewsbury, and his grandfather was the celebrated Dr Erasmus Darwin, whose life and writings have been previously noticed. At sixteen years of age, Charles Darwin went to Edinburgh to study medicine; but he soon made up his mind that the pursuit of medicine as a profession would not be in accordance with his tastes, and he accordingly betook himself in 1828 to Cambridge, with a view to studying theology. The influences of the place, however, combined, we may presume, with his own unconscious bent and aptitudes,

soon had the effect of so far awakening his early love of nature, that he ultimately threw himself almost entirely into scientific studies. This result was also in large part due to the intercourse which he enjoyed with Professor Henslow, the well-known botanist.

In 1831, Darwin graduated as Bachelor of Arts, and in the autumn of the same year his final life-course was determined for him by his appointment to the unpaid post of naturalist to the Beagle, a ten-gun brig, commanded by Captain (afterwards Admiral) Fitzroy, and then under orders to proceed on a long surveying voyage round the world. This cruise occupied five years of Darwin's life, and constituted the real great university in which he studied nature, and read for his degree.'* During this memorable voyage, he not only collected a vast amount of scientific material of all kinds, but he accumulated an endless store of observations which might, and ultimately did, serve as the groundwork for his magnum opus on the Origin of Species.

The

In October 1836, Darwin landed at Falmouth, after his long and profitable cruise in the Beagle. next three years were spent by him in London, his hands being fully occupied with preparing his journals for publication, and in making the needful editorial arrangements for the description of the great scientific collections which he had brought home with him. By the advice

* Grant Allen, 'Life of Charles Darwin.'

+ Darwin's 'Journal of Researches into the Geology and Natural History of the various Countries visited by H.M.S. Beagle' was published in 1839. The descriptions of the scientific collections were ultimately published in 'The Zoology of H.M.S. Beagle,' which appeared in 1840-44. In this magnificent work, the fossil mammals were described by Owen, the living mammals by Waterhouse, the birds by Gould, the fishes by Jenyns, and the reptiles by Bell.

of his friend Sir Charles Lyell-advice which his freedom from pecuniary necessities fortunately enabled him to take-Darwin, on his return home, sought no official scientific appointment. In 1839, he married his cousin, Miss Emma Wedgewood, and finally established himself at Down House, near Orpington, in Kent, which continued to be his home to the end of his life.

After his long voyage in the Beagle, Darwin never left England again, not even to pay a brief visit to the Continent. From his settlement at Down in 1839 onwards, he lived a quiet unostentatious life in his own home, unremittingly occupied with his scientific pursuits. On the 18th of April 1882, the great naturalist was attacked by sudden illness, and at four o'clock in the afternoon of the next day he breathed his last. He was buried in Westminster Abbey, in the presence of most of the foremost representatives of science in Britain; and his death deprived the scientific world of the most prominent figure that this generation has

seen.

With regard to the vast mass of scientific work which Darwin produced, nothing further can be attempted here than merely to mention the titles of his larger works. His 'Journal' of researches made in the voyage of the Beagle was, as we have seen, published in 1839. Other fruits of the long series of observations which he made on the same voyage were published later under the names of 'The Structure and Distribution of CoralReefs' (1842), 'Geological Observations on Volcanic Islands' (1844), and 'Geological Observations on South America' (1846). Many of Darwin's geological observa

tions (such as those on cleavage and foliation, on the structure of the 'pampas' of South America, and on volcanic islands) are of the highest importance and of permanent value; and his theory of the Origin of Coralreefs obtained a world-wide reputation. Darwin, as previously mentioned, also edited the 'Zoology of the Voyage of the Beagle.' Subsequently to his return to England, he engaged in special zoological researches, and published his classical 'Monograph of the Cirripedia,' printed by the Ray Society in 1853; with a companion volume on the fossil species of the same group, which appeared under the auspices of the Palæontographical Society. In 1859 appeared the first edition of the 'Origin of Species by means of Natural Selection,' which rendered his name at once famous over the whole civilised world, and which gave rise to more discussion than perhaps has ever been produced by any other scientific book whatever. This work has been translated into almost all European languages, and the English edition now generally used is the sixth, published in 1872. Among the works which proceeded from the pen of Dr Darwin during his later years may be enumerated 'The Fertilisation of Orchids' (1862); the 'Variations of Animals and Plants under Domestication' (1867); 'The Descent of Man and Selection in Relation to Sex' (1871); and 'The Expression of the Emotions in Man and Animals' (1873).

The great principle which Darwin established in connection with the highly complex problem of the Origin of Species, is what is known as 'the Theory of Natural Selection, or the Preservation of Favoured Races in the

Struggle for Life.' Mr Alfred Russell Wallace has a conjoint claim to the discovery of this principle, as he published similar views to those of Mr Darwin in a memoir entitled 'On the Tendency of Varieties to depart indefinitely from the Original Type,' which appeared in the Journal of the Linnean Society in 1859, in the same year as the first edition of the 'Origin of Species' was given to the world. It is, as has been seen, an error to regard Mr Darwin as the originator of the theory of Evolution, as applied to animals and plants. It is the 'Theory of Natural Selection'-a theory which explains how evolution has taken place-with which his name will be always associated; and it is this theory alone of which we propose here to give a general outline.

The bases of the Theory of Natural Selection' may be laid down in the following propositions :

(1) The first proposition in the Theory of Natural Selection embraces what has been called the 'Malthusian law of increase'-the law, namely, that all living beings tend to increase more rapidly than their means of subsistence. The tendency of living beings, in fact, is to increase in a geometrical ratio, and this is true not only of all animals but also of all plants. In support of this law it is not necessary to take the cases of animals so prolific as the cod, the female of which produces annually about ten millions of ova; for the same law is exemplified quite as well by the elephant, which is considered to be the slowest breeder of all animals. Upon this point Darwin has made an interesting calculation. The elephant begins to bear young