תשובה חלקית מצאתי במילות הסיכום מאמר
על המיפוי הראשוני של גנום השימפנזה:
http://www.nature.com/nature/journal/v437/n7055/full/nature04072.html
ברמה המולקולרית הנושא אכן סבוך ואפילו שאלה תמימה למראה הופכת לאתגר לא פשוט. ברוב תמימותי חשבתי שהפיצול הרב למינים רבים בענף המוביל לאדם הם אינדיקציה ברורה ללחץ הסלקטיבי שהוביל לאדם.
(את זה אתה תאהב משום הדגש על השפעתו של הסחף הגנטי):
The hardest such question is: what makes us human? The challenge lies in the fact that most evolutionary change is due to neutral drift. Adaptive changes comprise only a small minority of the total genetic variation between two species. As a result, the extent of phenotypic variation between organisms is not strictly related to the degree of sequence variation. For example, gross phenotypic variation between human and chimpanzee is much greater than between the mouse species Mus musculus and Mus spretus, although the sequence difference in the two cases is similar. On the other hand, dogs show considerable phenotypic variation despite having little overall sequence variation (~0.15%). Genomic comparison markedly narrows the search for the functionally important differences between species, but specific biological insights will be needed to sift the still-large list of candidates to separate adaptive changes from neutral background.
ועוד:
Our comparative analysis suggests that the patterns of molecular evolution in the hominids are typical of a broader class of mammals in many ways, but distinctive in certain respects. As with the murids, the most rapidly evolving gene families are those involved in reproduction and host defence. In contrast to the murids, however, hominids appear to experience substantially weaker negative selection; this probably reflects their smaller population size. Consequently, hominids accumulate deleterious mutations that would be eliminated by purifying selection in murids. This may be both an advantage and a disadvantage. Although decreased purifying selection may tend to erode overall fitness, it may also allow hominids to ‘explore’ larger regions of the fitness landscape and thereby achieve evolutionary adaptations that can only be reached by passing through intermediate states of inferior fitness
ומסר חינוכי של החוקרים לשימור השימפנזים:
Our close biological relatedness to chimpanzees not only allows unique insights into human biology, it also creates ethical obligations. Although the genome sequence was acquired without harm to chimpanzees, the availability of the sequence may increase pressure to use chimpanzees in experimentation.
