Again, touching the question of Heredity, Darwin concluded, on what is now generally regarded as insufficient evidence, that acquired characters are transmissible; and in order to show how this might be possible he promulgated what he termed a "provisional hypothesis of Pangenesis". But it is now recognised that the problems of Heredity still remain unsolved and that its laws have yet to be discovered. The transmissability of acquired characters has been called in question and is totally denied by a great number of leading biologists at the present day.
Darwin took Variation and Heredity as his basis and upon these two pillars he built up his theory of the origin of species and the evolution of organic forms. Biologists are now pushing their enquiries further back; they are not content to take Variation and Heredity as facts which require no further explanation. It is now realised that the causes of Variation must be understood and the laws of Heredity discovered before the problem of development can be fully solved. It is by the observation of what takes place at the earth's surface to-day, or that has taken place recently,that geologists have found the clue by means of which they can unravel the origin and history of the rocks which make up the crust. The present is always found to be the key to the past. It is only by employing a similar method that biologists can hope to attack successfully the problems of Variation and Heredity. By actual observation and experiment they must seek to determine how species are being
