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Considered the "father of evolutionary theory," Darwin made two contributions of enormous impact to the idea of evolution. First, Darwin marshaled substantial evidence for the theory of descent with modification, a kinematic theory that treats non-causal relations between things—it deals with the pattern of evolution. Secondly, Darwin proposed a mechanism for that observed pattern, the theory of natural selection. This is a dynamic theory that involves mechanisms and causal relationships—it deals with the process of evolution.
Darwin's theory of descent with modification, which is neutral with respect to the process involved, was accepted soon after its introduction, and substantial evidence has been accumulated in its support. In contrast, Darwin's theory of modification through natural selection was, at its core, revolutionary and controversial, positing a process that went against prevailing concepts at the time. It was not well accepted by the scientific community until the middle of the twentieth century. Furthermore, the theory that natural selection serves as the main directive force of large-scale evolutionary changes and new designs (macroevolution) remains controversial in various quarters today.
The abacus is a simple, inexpensive, yet powerful tool for calculation. Although electronic calculators are replacing it for practical reasons, the use of the abacus continues to be taught in technologically advanced countries such as Japan. Just as with popular board games such as chess, shogi, and go, local, regional, and national competitions in abacus use are held for students.