The reason humans, but no other primates, have been endowed with the ability to generate language is because the alpha motor neurons of the brain stem and spinal cord are innervated directly by neocortical neurons for maximal control over the vocal and handwriting musculature, and a similar control exists for reading via the ocular musculature (Tehovnik, Hasanbegović, and Chen 2025).  Moreover, the telencephalon (a neocortical homologue in vertebrates) is directly connected to brain stem motor neurons that subserve vocalization in songbirds (Schmidt and Wild 2014).  For all vertebrates, it is the alpha motor neurons that are ultimately linked to and put under the direct (or indirect) control of the neocortex/telencephalon to manage the skeletal musculature, and each alpha motor neuron is connected to but one muscle fibre to establish independent regulation of a fibre (but one alpha motor neuron can innervate many muscle fibres, called a motor unit, Sherrington 1906).

The number of alpha motor neurons is somewhat varied across vertebrates: the lamprey has 100,000 (Buchanan 2002; Wadden et al. 1997), the elephant has ~ 1,000,000 (ChatGPT, Nov 30, 2024; Kaufman et al. 2022), and the human has 150,000 to 250,000 (Buchthal 1961; Enoka 1995; McComas et al. 1971; Tehovnik et al. 2025; see Footnote 1).  Thus, the number of alpha motor neurons increases going from simple vertebrates such as the lamprey, which utilizes the neurons for swimming and eating, to elephants and humans, the latter of whom depend on neurons for sophisticated cognitive processes such as speaking, writing, and reading (see Footnote 2). Finally, the direct connectivity between the neocortex and the alpha motor neurons guarantees maximal control over the muscles involved in these processes, which requires a high degree of precision: signing one’s name on a document that one disagrees with can have dire consequences.

Footnotes:

Footnote 1: A cerebellum for the coordination of body movements (Eccles 1967) exists in the lamprey, the elephant, and the human. The size of the cerebellum in the lamprey is barely visible to the eye when dissecting the lamprey brain, whereas in the case of the elephant its cerebellum containing some 260 billion neurons which is about four times greater than the number of neurons in the human cerebellum at 69 billion neurons (Herculano-Houzel 2009; Herculano-Houzel et al. 2014). The augmentation in the size of the elephant cerebellum could be related to the number of alpha motor neurons: 100,000 in the lamprey, 1,000,000 in the elephant, and up to 250,000 in the human.

Footnote 2: For the vocal apparatus (e.g., the larnyx), one alpha motor neuron innervates 5 to 10 muscle fibres; for the fingers this ratio is 1 to 10 - 100, and for the eyes this ratio is 1 to 3 - 10. By comparison the gastrocnemius muscle has a ratio of 1 to 2,000. The lower the value, the more focused control an alpha motor neuron has over the individual elements of a muscle, which is what would be expected for speaking, writing, and reading.