It's easy to assume that every trait - including stubby arms on a terrifying predator - must be beneficial, but the forces of evolution don't really work like that.

If you liked this week’s video, we think you might also like: The BrainScoop on Sue the T. Rex: https://www.youtube.com/watch?v=HHhI4eqYGdk

Thanks to the University of Minnesota for sponsoring this video! http://twin-cities.umn.edu/ Thanks also to our supporters on https://www.patreon.com/MinuteEarth

LEARN MORE

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To learn more about this topic, start your googling with these keywords:

• Evolutionary Mechanisms: Forces that change the frequency of genes in populations.
• Natural Selection: The process whereby traits that make animals more likely to survive and reproduce take hold in a population.
• Vestigiality: The process by which a genetically-determined structure loses some or all of its functionality.
• Genetic Drift: A change in the frequency of an allele due to random sampling.

CREDITS

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Script Writer: David Goldenberg Script Editor: Kate Yoshida Video Illustrator: Qingyang Chen Video Director: Emily Elert Video Narrator: Kate Yoshida With Contributions From: Henry Reich, Alex Reich, Ever Salazar, Peter Reich Music by: Nathaniel Schroeder

MinuteEarth is produced by Neptune Studios LLC https://neptunestudios.info

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REFERENCES

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Switek, B. (2013). Paleontology: The Truth about the T. Rex 502 (424-426). Retrieved from: http://www.nature.com/news/palaeontology-the-truth-about-t-rex-1.13988

E. Snively, A. P. Russell, G. L. Powell, J. M. Theodor & M.J.Ryan (2014). The role of the neck in the feeding behaviour of the Tyrannosauridae: inference based on kinematics and muscle function of extant avians. Journal of Zoology 292 (290-303). Retrieved from: http://onlinelibrary.wiley.com/doi/10.1111/jzo.12109/abstract

Middleton, K., and Gatesy, S. (2000) Theropod forelimb design and evolution. Zoological Journal of the Linnean Society 128 (149-187). Retrieved from: http://onlinelibrary.wiley.com/doi/10.1111/j.1096-3642.2000.tb00160.x/abstract

Lynch, M., Ackerman, M., Gout, J., Long, H., Sung, W., Thomas, W., and Foster, P. (2016). Genetic drift, selection and the evolution of the mutation rate. Nature Reviews: Genetics 17 (704-715). Retrieved from: http://www.nature.com/nrg/journal/v17/n11/full/nrg.2016.104.html