Why Do We Have More Boys Than Girls?

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Created by Henry Reich
Production and Writing Team: Alex Reich, Peter Reich, Emily Elert, Ever Salazar, Kate Yoshida, and Henry Reich
Music by Nathaniel Schroeder:
Narrated by: Emily Elert
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MinuteEarth provides an energetic and entertaining view of trends in earth's environment -- in just a few minutes!
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References
Cameron, E.Z. (2004). Facultative adjustment of mammalian sex ratios in support of the Trivers-Willard hypothesis: evidence for a mechanism. Proceedings of the Royal Society of London Series B 271:1723–1728.
Chahnazarian, A. (1988). Determinants of the sex ratio at birth: Review of recent literature. Social Biology 35 (3–4): 214–235.
Coale, A.J. (1991). Excess female mortality and the balance of the sexes in the population: An estimate of the number of "missing females." Population and Development Review 17(3): 517-523.
Clutton-Brock, T. H., Albon, S. D., and Guinness, F. E. (1986). Great expectations: dominance, breeding success and offspring sex ratios in red deer. Animal Behavior 34: 460-471.
Kalben B. (2000). Why men die younger: causes of mortality differences by sex. North American Actuarial Journal 4(4): 83–111.
Schnettler, S. (2013). Revisiting a Sample of U.S. Billionaires: How Sample Selection and Timing of Maternal Condition Influence Findings on the Trivers-Willard Effect. PLoS ONE 8(2): e57446.
Song, S. (2012). Does famine influence sex ratio at birth? Evidence from the 1959–1961 Great Leap Forward Famine in China. Proceedings of the Royal Society B 279(1739):2883-2890.
Thogerson C.M., Brady, C.M., Howard, R.D., Mason, G.J., Pajor, E.A., Vicino, G.A., and Garner, J.P. (2013) Winning the genetic lottery: biasing birth sex ratio results in more grandchildren. PLoS One 8(7):e67867.
Trivers, R.L., and Willard, D.E. (1973). Natural selection of parental ability to vary the sex ratio of offspring. Science 179: 90-92.
Photo credits:
Elephant Seal 1
Photo by: Roy Mangersnes
Elephant Seal 2
Photo by: Mike Baird
White tailed deer
Photo by: Public Domain
Key Deer
Photo by: IanarÈ SÈvi
Male Lion
Photo by: Wikimedia user Robek
Baby Lion
Photo by: Flickr user fortherock
Brad Pitt
Photo by: Foreign and Commonwealth Office
Kids
Photo by: Barbara Hobbs