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Being a giraffe
is not easy. To pump blood two meters up from the chest to the
brain calls for a turbo-charged heart and twice the blood
pressure of other mammals. Giraffes also need special safety
valves to let them bend down for a drink and raise their heads
again without fainting.
The animals' unique body configuration has long been a puzzle
for biologists, including Charles Darwin.
Now, by comparing the genome of the giraffe with its closest
relative, the short-necked okapi, scientists have unpicked part
of the puzzle by pinpointing changes in a small number of genes
responsible both for regulating body shape and circulation.
This suggests that the development of a long neck and a powerful
heart went hand in hand, driven by a relatively small number of
genetic changes.
"There are many theories about how the giraffe's neck lengthened
but it does seem that the development of the cardiovascular
system evolved in parallel with the development of the skeletal
system," said Morris Agaba of the African Institute for Science
and Technology in Tanzania.
He and colleagues published their findings in the journal Nature
Communications on Tuesday.
The unraveling of the genetic factors behind the giraffe's
remarkable cardiovascular system could also be instructive for
human health, since the animals appear to avoid the kind of
organ damage often found in people with high blood pressure.
The more fundamental question of why giraffes evolved their long
necks remains open, however.
The apparently self-evident idea that it was to reach
ever-higher food supplies has been challenged in the past 20
years by a competing hypothesis that is it is actually due to
sexual selection and competition among fighting males for mates.
Unlike long-necked birds, which have additional vertebrae,
giraffes have the same seven vertebrae found in all mammals,
although theirs are greatly extended.
(Reporting by Ben Hirschler; Editing by Andrew Heavens)
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