A brief answer is the only one that can be given to the fairly newly emergent field of interdisciplinary linguistic study, biolinguistics. According to renowned linguist Noam Chomsky (2004), the first and "most far-reaching" conference on biolinguistics, organized to discuss "the biolinguistic perspective," was held in 1974 and coined "biolinguistics" in the title of the conference, "Biolinguistics." Chomsky asserts that the questions raised at this conference still govern the search for data in today's biolinguistics studies.
As explained by Chomsky, from whom this entire answer will be drawn, biolinguistics considers all aspects of language ("sound, meaning, structure") as being a "state of some component of the mind." Mind is defined as the outcome of a process of the brain, a process of "emergences" that "we do not yet understand," according to Vernon Mountcastle. Biolinguistics is a science that relies upon "Newton's separation" of the mind-body duality, so that "no coherent mind-body problem remains" and so that all things falling under the designation of mental processes may be identified as and examined as what Joseph Priestley said were the result of the "organic structure of the brain."
The thesis in force in biolinguistics is that language, the focus of biolinguistics, is an entirely natural phenomenon "caused by the neurophysiological activities of the brain." This opposes earlier ideas such as those posited by Locke and Alfred Wallace asserting that mental functions--such as cognition, moral judgement, imagination, language, even personality--could not be explained by evolutionary principles alone but required recourse to the existence of an external power, force, or will to provide reasonable explanation: for Locke it was God and a “superadded” faculty, whereas for Wallace it was some unidentified additional universal force along the lines of the nature of gravity or cohesion. Thus biolinguistics represents a controversial (now as well as earlier) and radically new approach to mental "emergences" and linguistics. Present research is greatly aided by technological innovations such as fMRI and PET Scans. This is a brief encapsulized summary of biolinguistics.
Basically, a bio-linguist tries to find out the how, the why, and the functions of the brain necessary for human language to be produced.
Whereas brain research is now in its hey day with so much information becoming available and then the opportunity to merge all this with linguistic data collected overtime there is continuing opportunity to learn more and more about this field of study.
Another aspect of bio-linguistics is the study of how speech and language evolved in humans.
See Chomsky: The biolinguistic perspective views a person’s language in all of its aspects – sound, meaning, structure -- as a state of some component of the mind, understanding “mind” in the sense of 18th century scientists who recognized that after Newton’s demolition of the “mechanical philosophy,” based on the intuitive concept of a material world, no coherent mind-body problem remains, and we can only regard aspects of the world “termed mental,” as the result of “such an organical structure as that of the brain,” as chemist-philosopher Joseph Priestley observed. Thought is a “little agitation of the brain,” David Hume remarked; and as Darwin commented a century later, there is no reason why “thought, being a secretion of the brain,” should be considered “more wonderful than gravity, a property of matter.” By then, the more tempered view of the goals of science that Newton introduced had become scientific common sense: Newton’s reluctant conclusion that we must be satisfied with the fact that universal gravity exists, even if we cannot explain it in terms of the self-evident "mechanical philosophy." As many commentators have observed, this intellectual move "set forth a new view of science" in which the goal is "not to seek ultimate explanations" but to find the best theoretical account we can of the phenomena of experience and experiment