Heterochrony

Question 1

What is heterochrony?

Answer 1

Heterochrony is an evolutionary mechanism in which different developmental processes accelerate or retard relative to each other.

1. Neonety: somatic development is retarded; sexual development is normal
2. Paedomorphosis: somatic development is stopped; sexual development is normal
3. Progenesis: reproductive development is normal
4. Peramorphosis: somatic development is accelerated

Question 2

What are some neotenic traits in humans?

Answer 2

1. Skull:
   
   • orthognathic face
   • high vault in skull roof
   • large, rounded eye socket
   • slight torus supraorbitalis
   • light gabella
   • thin skull bone
   • small jaw
     The neonety of the skull is stronger in female, probably due to sexual preference, which caused sexual dismorphism.
2. Brain:
   
   • postponement brain maturation
   • extension of juvinile period
   • presence of parents to learn from
   • flexibility and learning
   • no instinctual behaviour
   • no developmental canalization of behaviour
3. Life cycle:
   
   • total lifespan and juvinile period extended
4. Nakedness:
   
   • partner preference
   • less parasitic load
   • acquatic ape
   • energy
   • loss of keratin genes