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Why did numerical taxonomy use large numbers of observable traits?

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A diagram showing the hierarchy of animal classification in taxonomy, with colored boxes arranged from broadest to most specific: domain, kingdom, phylum, class, order, family, genus, and species. — taxonomy Animals and other organisms are classified within a succession of nested groups that ranges from the general to the particular.

Numerical taxonomy, also known as phenetics, utilized large numbers of observable phenotypic characteristics primarily in the name of objectivity. By counting as many characters as possible and giving them equal weight, proponents sought to classify organisms based strictly on overall similarity rather than evolutionary history.12

In this approach, the classification was determined by the total number of shared traits: the more characteristics two organisms had in common, the more closely they were classified together. This method intentionally disregarded ancestry, as pheneticists believed that focusing on a broad, quantified set of observable features would provide a more neutral and reproducible basis for taxonomy than subjective interpretations of evolutionary relationships. However, because the selection and definition of these traits often required subjective decisions, the method eventually faced criticism regarding its scientific credibility, leading many taxonomists to move toward cladistics instead.13