The giraffe genome

Is believed to have been the changes from extensive forests to more open habitats, which began 8 mya.[11] During this time, tropical plants disappeared and were replaced by arid C4 plants, and a dry savannah emerged across eastern and northern Africa and western India.[16][17] Some researchers have hypothesised that this new habitat coupled with a different diet, including acacia species, may have exposed giraffe ancestors to toxins that caused higher mutation rates and a higher rate of evolution.[18] The coat patterns of modern giraffes may also have coincided with these habitat changes. Asian giraffes are hypothesised to have had more okapi-like colourations.[11]

The giraffe genome is around 2.9 billion base pairs in length compared to the 3.3 billion base pairs of the okapi. Of the proteins in giraffe and okapi genes, 19.4% are identical. The two species are equally distantly related to cattle, suggesting the giraffe’s unique characteristics are not because of faster evolution. The divergence of giraffe and okapi lineages dates to around 11.5 mya. A small group of regulatory genes in the giraffe appear to be responsible for the animal’s stature and associated circulatory adaptations.[19]

Species and subspecies

“Approximate geographic ranges, fur patterns, and phylogenetic relationships between some giraffe subspecies based on mitochondrial DNA sequences. Colored dots on the map represent sampling localities. The phylogenetic tree is a maximum-likelihood phylogram based on samples from 266 giraffes. Asterisks along branches correspond to node values of more than 90% bootstrap support. Stars at branch tips identify paraphyletic haplotypes found in Maasai and reticulated giraffes”.[20]
The IUCN and most giraffe scientists currently recognise only one species of giraffe with nine subspecies.[21][22] During the 1900s, various taxonomies with 2 or 3 species were proposed.[23] In 2001, a two-species taxonomy was proposed.[24] A 2007 study on the genetics of giraffes, suggested six species.[20] A 2011 study using detailed analyses of the morphology of giraffes, and application of the phylogenetic species concept, described eight species of living giraffes.[25] A 2016 study also concluded that living giraffes consist of multiple species. The researchers suggested the existence of four species, which have not exchanged genetic information between each other for 1 to 2 million years.[26] Since then, a response to this publication has been published, highlighting seven problems in data interpretation, and concludes “the conclusions should not be accepted unconditionally”.[27]