m**c
发帖数: 7349 | 1 The giraffe and the okapi's common ancestor had an intermediate neck length,
implying that when they split off about 11.5 millions years ago, the okapi
evolved to have shorter necks, Dr. Cavener tells the Monitor. As they
evolved separately, the giraffe's key regulatory proteins genes underwent
several modifications, promoting extended growth in the cervical vertebrae
and the cardiovascular system, allowing the giraffe's heart to pump blood
all the way up to its head.
Making that six-and-a-half foot journey upward has "evolved a turbocharged
heart" and a vascular system adapted to handle twice the blood pressure as
in other animals, the researchers write.
But it is modification, not a question of "new genes," responsible for the
evolution of the giraffe's neck, Cavener tells the Monitor. "The message is
that novelty is not created from scratch, but rather from building on
solutions that have evolved over time. The giraffe's long neck and legs are
kind of a good example. | m**c
发帖数: 7349 | |
|
