Giraffes (G. camelopardalis) are known for their distinct long necks and there are two main hypotheses that claim to explain their evolution. One hypothesis states that giraffes developed long necks to allow them to browse high in tree canopies (Wilkinson & Ruxton, 2012). Another suggests a ‘necks-for- sex’ hypothesis, in which the origin is due to sexual selection in competing male giraffes (Simmons & Altwegg, 2010). Wilkinson & Ruxton (2012) examine these hypotheses by first repudiating Simmons & Altwegg’s (2010) argument. Simmons & Altwegg (2010) argue that if sexual selection contributed to the evolution of giraffes, there would be differences in head mass between the sexes. Conversely, Simmons & Altwegg (2010) also state that if competition in food resources is the only reason for elongated necks, then there should be no expected difference in head mass between sexes. Mitchell et al. (2009) viewed Simmons & Altwegg’s (2010) argument and examined growth patterns of male and female giraffes. Badlangana et al., (2009) also observed neck length and focuses on examining vertebral columns of giraffes to determine their evolution, in relation to the hypothesis of sexual selection. While the more commonly known and accepted argument is that giraffe necks elongated for reaching nutritional resources, the more rejected yet controversial argument of giraffe neck evolution as a result of sexual selection has enough justification to be plausible.

Mitchell et al. (2009) measured body mass (kg), total length (cm), total height (cm), foreleg length (cm), neck length (cm), neck length: foreleg length ratio (NL:FLL), head and neck mass (kg), and cervical vertebrae mass (kg) and found no significant differences between sexes. Data analyses for these measurements were made by developing log equations for each variable with respect to body mass. Mitchell et al. (2009) state that head mass was the same for both sexes, and mean head mass for males and females constituted 2.9% of the mean body and 2.5% of the mean body, respectively. Mitchell et al.’s (2009) data also show that the proportion of neck mass that was bone mass declined slightly during growth from birth to maturity from 14% to 10%. On the other hand, in females the contribution of vertebrae was more uniform, staying at 10% of neck mass both at birth and at maturity. Simmons & Altwegg (2010) analyzed all the presented information and continued to refute it.

Simmons & Altwegg (2010) argue that sexual selection does not directly predict longer necks, but more powerful ones for males. Simmons & Altwegg (2010) state that female necks can be just as long as male necks, but are ineffective for clubbing because sparring of necks combines neck length and neck size to produce momentum in the neck to club rivals. Simmons & Altwegg (2010) also state that differentiating the muscle to bone components in the neck indeed show that the mass difference is due to muscle mass and not due to bone density. For same-length skulls, male skulls were actually found to be about four times heavier than female skulls (Simmons & Altwegg 2010) and while both sexes continued to grow, males grew more by depositing 14.8 kg superficial bone over their skulls compared to females who only had 3.0 kg. Simmons & Altwegg’s data compared to Mitchell et al.’s (2009) focuses more on the weight of giraffe heads which is necessary for neck sparring, while Mitchell et al. (2009) focuses on the actual neck length and uses that to show that there is little difference between the genders. Even with the given information it is still difficult to fully explain which of the hypotheses is correct.