The Indo-European languages are a language family of several hundred related languages and dialects. There are about 445 living Indo-European languages, according to the estimate by Ethnologue, with over two-thirds of them belonging to the Indo-Iranian branch. The most widely spoken Indo-European languages by native speakers are Spanish, English, Hindustani (Hindi and Urdu), Portuguese, Bengali, Russian, and Punjabi, each with over 100 million speakers. Today, 46% of the human population speaks an Indo-European language as a first language, by far the highest of any language family. The Indo-European family includes most of the modern languages of Europe, and parts of Western, Central, and South Asia. All Indo-European languages are descendants of a single prehistoric language, reconstructed as Proto-Indo-European, spoken sometime in the Neolithic era. Languages of the Indo-European family are classified as either centum languages or satem languages according to how the dorsal consonants (sounds of "K" and "G" type) of the reconstructed Proto-Indo-European language (PIE) developed. The canonical centum languages of the Indo-European family are the "western" branches: Hellenic, Celtic, Italic and Germanic.