Second Major



Dunsworth, Holly

Advisor Department

Sociology and Anthropology




Taillessness; Tail Loss; Hominoids; Primates; Genetics; Catarrhine


Investigating the Genetic Basis for Hominoid Taillessness:

A Comparative Genetic Approach Across Ten Catarrhine Taxa

Samantha Tickey-McCrane1,2, Johanna E. Wegener2, and Holly Dunsworth1

Honors Thesis Abstract Written by Samantha Tickey-McCrane, Departments of Anthropology & Biology

Advisor: Dr. Holly Dunsworth, Department of Anthropology

How did hominoid tail loss occur? My goals are to test phylogenetic and adaptive hypotheses for tail length variation among macaques, and use those insights to reconstruct the evolution of hominoid taillessness. Further, I aim to ultimately uncover which candidate genes or pathways may be responsible for catarrhine tail loss, and what other traits may be affected by these developmental and genetic pathways.

I explored published catarrhine vertebral counts and phylogenies in the literature. I also collected data from 95 Macaca and Papio individuals in the collections at the American Museum of Natural History, NY. Based on known mechanisms of tail formation in embryos, I identified the genes that might be responsible for the interruption of tail development. I took these candidates to the annotated whole genomes of catarrhine primates and used a comparative approach across 10 taxa. I also focused on cis-regulatory regions 1,000 base pairs upstream of the candidate genes, that may have been involved in gene regulation.

Regarding the skeletal data, there appears to be a pattern where tail length variation is determined by factors of 3-4 caudal vertebrae, suggesting a segmental basis for the genetic factors involved. My preliminary genomic analyses indicate that comparing candidate genes is valuable, but is only a first step because regulatory non-exonic elements associated with these genes are more likely to be involved in taillessness. Investigating the developmental and genetic bases of tail variation among Macaca holds great promise for reconstructing the evolutionary history of hominoid taillessness and its consequences. Future studies continuing to probe whole genomes and the expansion of available primate genomes will make this possible.

If we can discover the underlying genetic mechanisms for taillessness, we can reconstruct the evolution of this significant feature that we share with apes, and that may have been a necessary precursor to bipedalism.


Thank you to Johanna E. Wegener and Dr. Holly Dunsworth of the University of Rhode Island for their continual mentorship in a new area of study for me, collaboration, and support.