Question: What did the Mexican Tetra lose during it's evolution?
About the article "Evolution", section "Applications".

Candidate passages:
Summer, 2000.
Eleven year old Yusuke and his classmates are camping in a woods when suddenly they see a bright light streak over the treetops and into the woods.
The boys take off into the woods towards the light.
There in the ground, growing, they find a small round metallic object.
Just as Yusuke reaches to touch it, the mysterious object up pops a set of eyes and the object says;"I am Tetra, I meet Yusuke".
Startled Yusuke replies "Your name is Tetra?
Cool!
"Tetra is kept from adult eyes in Yusuke's closet.
Tetra creates wonderful gadgets using "never-seen-before" technology.
It would appear Tetra was designed with artificial intelligence.
But where did Tetra come from and what is its purpose?
As the relationship grows between Yusuke and Tatra, these questions are answered. 
Artevea (formerly, Simoco Digital UK Limited), initially originated from the Pye Telecommunications and Philips business operations, which from its foundation in Cambridge during the 20th century initiated the TETRA Digital evolution during its development in the 90’s as Simoco. 
The blind form of the Mexican tetra is different from the surface-dwelling form in a number of ways, including having unpigmented skin, having a better olfactory sense by having taste buds all over its head, and by being able to store four times more energy as fat, allowing it to deal with irregular food supplies more effectively.
However, its lack of eyes has been at the center of discussion of the Mexican cave tetras among creationists.
Darwin said of sightless fish:Modern genetics has made clear that the lack of use does not, in itself, necessitate a feature's disappearance.
[http://www.findarticles.com/p/articles/mi_m1134/is_5_114/ai_n13811128] In this context, the positive genetic benefits have to be considered, i.e., what advantages are obtained by cave-dwelling tetras by losing their eyes?
Possible explanations include: Not developing eyes allows the individual more energy for growth and reproduction.
[http://www.daylightatheism.org/2006/02/evolved-minds.html] There remains less chance of accidental damage and infection, since the previously useless and exposed organ is sealed with a flap of protective skin.
Another likely explanation for the loss of its eyes is that of selective neutrality and genetic drift; in the dark environment of the cave, the eyes are neither advantageous nor disadvantageous and thus any genetic factors that might impair the eyes (or their development) can take hold with no consequence on the individual or species.
Because there is no selection pressure for sight in this environment, any number of genetic abnormalities that give rise to the damage or loss of eyes could proliferate among the population with no effect on the fitness of the population.
Among some creationists, the cave tetra is seen as evidence 'against' evolution.
One argument claims this is an instance of "devolution"—showing an evolutionary trend of decreasing complexity.
But evolution is a nondirectional process, and while increased complexity is a common effect, there is no reason why evolution cannot tend towards simplicity if that makes an organism better suited to its environment.
Research by MIT biology professor Susan Lindquist shows that inhibition of the HSP90 protein has a dramatic effect in the development of the blind tetra.
This research is seen by creationists as evidence of "built-in adaptability, not slow and gradual evolution."
"A. mexicanus" is famous for its blind cave form, which is known by such names as blind cave tetra, blind tetra, and blind cavefish.
These forms have lost their sight and even their eyes.
These fish can still, however, find their way around by means of their lateral lines, which are highly sensitive to fluctuating water pressure.
Currently, 29 cave populations are known, dispersed over three geographically distinct areas in a karst region of northeastern Mexico.
Recent studies suggest at least two distinct genetic lineages occur among the blind populations, and the current distribution of populations arose by at least five independent invasions.
The eyed and eyeless forms of "A. mexicanus," being members of the same species, are closely related and can interbreed making this species an excellent model organism for examining convergent and parallel evolution, regressive evolution in cave animals, and the genetic basis of regressive traits.
"Astyanax jordani", another blind cave fish, is sometimes confused with the cave form of "A.
mexicanus."