BEIJING, Nov. 21 (Xinhuanet) -- A team of scientists
thinks our ancient predecessors developed vertebrae and a backbone to stiffen
their bodies so they could swim more powerfully and has developed robot tadpoles
to help prove the theory.
The far-distant forebearers of humans and other
vertebrates were much softer than their descendants. Instead of backbones they
had flexible rods know as notochords. By evolving vertebrae the attached muscles
could generate more force.
"The fossil record shows vertebrae evolved
independently at least four separate times. That shows they must really be
functionally important," said vertebrate physiologist John Long at Vassar
College in Poughkeepsie, N.Y.
To test this idea, Long and his colleagues built
robot fish with backbones of varying strength to simulate extinct animals. They
then "mated" the best swimmers to see how generations of "offspring" evolved to
The robots -- "Tadros" -- were modeled after the
larvae of marine animals known as sea squirts, swimming creatures that still
Each Tadro had a single electronic eye, a motor, a
computerized brain that controlled its motions, and tails made of gelatin of
different lengths and stiffness. The robots had bodies between six and seven
inches long, with tails two to four inches long, and swam along the surface.
The scientists raced three robots in
eight-foot-diameter fish tanks, each swimming to and around a light hanging
above the tank.
After seeing which fish swam best, the research team
"mated" them using computer simulations that modeled the genetic mixing that
occurs during sex to produce the next generation of Tadro tails. The best
swimmer was given the greatest mating success and opportunity to pass along its
traits, while poorer swimmers were less fortunate.
After 10 generations, Long and his colleagues found
that as swimming performances improved, stiffer tails evolved.
"One thing vertebrates really brought to scene were
large, fast, active animals, and this part of the anatomy has a direct
connection with that," Long said.
But Long said that only 40 percent of the increased
swimming efficiency could be related to stiffer tails, which meant other factors
were involved, including how easily the tail turns.
"We plan to investigate what that next 60 percent
is," Long said.
The research team intends to add a "predator" into
the tank during the next swimming competition to see how Tadro tails evolve
then. This hunter will try to collide with the robots, while the Tadros will try
to avoid it.
This next generation of Tadros will detect the
predator using infrared sensors that mimic the pressure-sensitive organs of
fish, known as lateral lines.
"We also plan not just on making the backbone
stiffer, but on putting in vertebrae, to make them bend, to have joints, and see
how that changes things," Long said.
Long and his colleagues reported their findings
online Nov. 17 in the Journal of Experimental Biology.