The onward march of evolving consciousness from one species to another proceeds step-by-step and very rarely by leaps. But the diverse steps in onward evolution must not be rigidly construed. If a particular species is extinct its spiritual purpose can be served by some other kindred species, or by added births in some complementary species, or by deficient and partial expressions through a slightly higher species. In short, evolution takes advantage of innumerable alternatives available to it. It can never be frustrated by minor gaps constituted by extinct species or missing links.
Even if the kangaroos, whooping cranes or any other species of plants or animals become extinct, it will neither arrest nor hamper the advancing life-stream. Nor will it frustrate the real purpose of evolution, which is to arrive at full consciousness. Even if there were a hundred missing links, the advancing life stream can either forge new suitable species or make use of existing species.
However, an interesting fact which needs special mention is that at the transition from one species to another species, there is for every such transition a sub-species or a form which is double-faced. It can, as it were, not only look in two opposite directions but also move in two opposite directions. With equal facility it can retain its contact both with the species from which it is disengaging and with the new species into which it is becoming moulded. This intermediate form has to be able to move backwards and forwards. It is absolutely necessary for transitions from one species into another.
– Beam, p20