What the title says, how can a biped human-like species evolve with decreased sexual dimorphism without compromising their survivability over the span of time?
- The species inhabit a planet with conditions, environment and biosphere similar to Earth.
- Technologically, they are on same level as humans.
- No magic, no aliens, no miracles.
Similarity (to humans):
- Evolutionary line (evolved from primates)
- Biped, similar internal anatomy.
- Dioecious (seperate sexes)
Same height, nearly equivalent weight, androgynic features
Less pronounced voice box (adam's apple) in males
Males with less broad shoulder (or opposite, with females having naturally broader shoulder) and less muscular overall.
Males with slightly wider pelvic region (decresing pelvic girth can be fatal for female, though why would it increase in males, escapes me.)
Secondary sexual characters less pronounced:
- smaller sized breast being average,
- more high pitch voice in males,
- overall, little to non-existent facial and sparse body hair in males and females
Note: The species in not wholly without sexual dimorphism but they are as minimium as they can get. (as one can see from aforementioned soft limits).
Sexual dimorphism in humans is down to many factors and in many cases to cope with survival pressure.
One example, both sexes increased in stature, but females grew disproportionately larger (to an extent decreasing stature dimorphism) because of complex parturition. Tall height of females helped in increasing pelvic size without increasing valgus angle, giving them an opportunity to accommodate heavier babies which is advantageous because of their largely altrical (helpless) nature due to bigger brain size of newborn infant.
Another dissimilarity is in body mass: In a data sample from 129 nations men averaged 14.2 and 12% heavier than women. Women have considerably more fat and men have more lean (and muscle) mass . It is less pronounced in infants and children and increase dramatically with puberty (Lean body mass comprises organ, muscles, bones, etc)
For better understanding, visit this article on sexual dimorphism.
In account of all this, despite some complications, the anatomical and morphological body plan of humans is extremely efficient and had survived various selection pressures.
Taking note, is there any way a human-like species would evolve with decreased sexual dimorphism and more similarity in stature, weight, body structure, facial feature?
If so, how would it effect the behavioral, social aspect of this species?
Edit: I am asking, what would promote minimum/reduced sexual dimorphism in a hominid-like species (such that breast/ penis are only reliable external sex indicator of a person). Would it be fatal? How would it effect us?
(Don't know why the text in 'Edit Summary' section isn't showing up on main page.)