Frietson Galis

Analysing vertebral columns of mammals

Our research focuses on innovations and mechanisms that facilitate or constrain evolutionary changes of body plans . We want to understand questions such as: Why do we have two eyes, two lungs, four limbs and seven neck vertebrae. To understand this, we study both why such traits can hardly ever change in evolution and why, exceptionally, changes are possible. Our data have implications for biodiversity, human morbidity and lethality.


Body plan evolution, developmental constraints, phylotypic stage, vertebral column, digits, human evolution, Evo-Devo, regeneration, parthenogenesis, cichlids, phenotypic plasticity, cognitive science


Dr. Frietson Galis

Senior researcher
Endless Forms
+31 (0)648814360


  • Conservation of phylotypic stages
  • Conservation of the number of seven neck vertebrae in mammals
  • Why is the number of trunk vertebrae variable in slow mammals, but conserved in fast ones, including humans
  • Evolution of digit numbers
  • Developmental constraints against parthenogenesis

Why do almost all mammals have seven cervical vertebrae? The mammalian vertebral column is highly variable, reflecting adaptations to a wide range of lifestyles. However, the number of neck vertebrae is surprizingly constant. Variations occur within humans, but almost only in individuals that die before birth or as neonate (~90% is dead around birth). The number variations themselves are usually not problematic, but they are strongly associated with harmful side-effects, including congenital abnormalities of all organ systems. There is, therefore strong selection against individuals with abnormal numbers. After birth there is further selection because of an increased incidence of paediatric tumors and lower fertility. Data on other mammals support an association of the number variations with congenital abnormalities. Exceptionally the super slow sloths and manatees can tolerate many of the normally deleterious side-effects, which has apparently allowed them to evolve abnormal cervical vertebral numbers.

Photographs: Joris van Alphen

Skeleton hallway - Joris van Alphen
Dorcas Gazelle skeleton - Joris van Alphen


Developmental constraints-Phylotypic stages-Evolution and development of the vertebral column-Evolution and development of digits-Phenotypic plasticity-Parthenogenesis-Regeneration


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