New Insights into the Evolution of Learned Vocalization from the Australian Zebra Finch, Taeniopygia castanotis

Author

Matthew Henry Davenport

Date of Award

2024

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Abstract

The common goal of my thesis is to understand the causative events in evolution that produced a clade of song learning birds from non-song learning ancestors.This information is important for shedding light on the evolution of spoken language in our own human lineage, where evolutionary analyses are technically limited. The most recent common ancestor of humans and chimpanzees was presumably a vocal non-learning African ape, alive ~6 mya. At some point between this ancestor and the emergence of modern humans 0.5 mya we evolved more dexterous hand control, bipedalism, light colored eyes, larger brains, less hair, weaker muscles, higher intelligence, greater eusociality, novel sweat glands, and spoken language; to name a few of the traits which separate us from other apes. As there are no extant species internal to this branch lacking one or more of these human specific phenotypes, it is much more difficult to ascribe observed human genome variation to the evolution of specific traits, especially behavioral traits. Further, neutral mutations cannot be removed by looking for shared variance across species because we are the only extant species of vocal learning primates. Human language is also difficult to isolate from a neuroanatomical perspective. Our current interpretation of the literature is that the neurons responsible for the learned movements of speech are either directly adjacent to or intermixed with those moving the hand and face in all primates, making them more difficult to localize. None of these limitations apply in oscine songbirds. In oscines, the vocal learning brain system is more segregated from non-vocal movements; There are over 4000 oscines, and most if not all are thought to be vocal learners; their suboscine outgroup clade is also species rich and consists of many vocal non-learners. Since oscine vocal learning neural circuits are discrete, potentially causative genes can be identified based upon their specialized expression within these circuits under various conditions. A subset of these genes have been found to have similar specializations in human speech brain regions, and thus these potentially trait-causative genes from songbirds can then be studied in the context of human evolution for the same trait using comparative genomics, as we begin to do here. I hope that these experiments and analyses can serve as the beginnings of a framework for future experiments seeking to understand our own evolution through the study of human-convergent traits in non-human lineages.

Comments

A Thesis Presented to the Faculty of The Rockefeller University in Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy

Recommended Citation

Davenport, Matthew Henry, "New Insights into the Evolution of Learned Vocalization from the Australian Zebra Finch, Taeniopygia castanotis" (2024). Student Theses and Dissertations. 757.
https://digitalcommons.rockefeller.edu/student_theses_and_dissertations/757