The thumbs of Ardipithecus ramidus, an early hominin, are almost as robust as in humans, so this may be a primitive trait, while the palms of other extant higher primates are elongated to the extent that some of the thumbs original function has been lost (most notably in highly arboreal primates such as the spider monkey). In humans, the big toe is thus more derived than the thumb.There is a hypothesis suggesting the form of the modern human hand is especially conducive to the formation of a compact fist, presumably for fighting purposes. The fist is compact and thus effective as a weapon. It also provides protection for the fingers. However, this is not widely accepted to be one of the primary selective pressures acting on hand morphology throughout human evolution, with tool use and production being thought to be far more influential. Additional images
See also
References
External links

Hand anatomy (eMedicine)
Film Board of Canada documentary Faces of the Hand
"The Common Hand" article in the May 2012 National Geographic
Authors review the previous pathogenic theories, discuss the link between concentric sclerosis and Liesegangs periodic precipitation phenomenon and propose a new mechanism based on self-organization. Clinical courses
It that the clinical course is primary progressive, but a relapsing-remitting course has been reported. It seems that the course gets better with prednisone therapy, although evidence of this is anecdotal and such conclusions are difficult to accept given that there are cases where patients spontaneously recover whether the patient was on steroid therapy or not.Baló lesions can disappear over time, but it has also been reported that the disease can convert to RRMSThe clinical course of Balo-like lesions also depends to the context in which they appear. Balo-like lesions have been reported in aquaporin-4 seropositive and seronegative NMOSD, and also in children, as part of an ADEM-like presentation

Diagnosis
Lesions under MRI are distinctive due to their natural concentric shape.Under a lumbar puncture CSF test, with Balós concentric sclerosis, as well as patients with pattern III lesions, were recently shown to be mostly negative for CSF-restricted oligoclonal bands. Also pattern III patients tend to be negative under the MRZ-reaction (measles, rubeola and zoster viruses)

Paediatric cases
Balós concentric sclerosis in children has been reported to behave different from adults

Lesions in autopsy and biopsy
A report comparing 1H-magnetic resonance spectroscopy, magnetization transfer and diffusion tensor imaging with histopathology in a patient with Balós concentric sclerosis, found that inflammation was traced by fractional anisotropy and increased lactate.