Identical vs. Fraternal

Are they identical or fraternal twins?


There are two different types of twins. "Dyzygotic (DZ) or fraternal twins result when two sperm fertilize two ova in the same menstrual cycle" (Stromswold 337).Then two zygotes are created and each of these zygotes is developing its own placenta. They evolve out of two eggs. Identical twins are created "when a single zygote (that originates from the fertilization of one ovum by a single sperm) divides in two" (Stromswold 337) and hence are called monozygotic (MZ) twins and evolve out of one egg. If monozygotic twins develop, they can either be two females ore two males, but the sexes cannot be mixed, whereas the dyzygotic twins can have same-sex pairs or a pair of two different sexes.

Helen Koch ascribed different characteristics to each type of twin, where she even segments the fraternal mixed-sex group into different characteristics:

Male identicals characteristic:

  • Are slower mentally on average, low in gregariousness and rather nonaggressive
  • Passivity and low social initiative, low rivalrousness, low aggressiveness
  • Rather low in speech
  • Very close (Koch 157-158)

Female identical characteristics:

  • Relatively short in stature at school age
  • Low originality and speech form
  • More interests than singletons
  • Socially more involved (both children and adults)
  • More popular, cheerful and good in leadership
  • More adult centered
  • Feminine girls (Koch 160-161)

Fraternal males (same-sex):

  • light in weight
  • syntax-error score was lower compared to identicals
  • less close
  • less frequently played together and dressed the same
  • more aggressive and gregarious
  • higher in leadership, more insistent on their rights, more involved with children, more selfish, indirect, exhibitionistic
  • more female playmates (Koch 158)

fraternal mixed-sexes, boys:

  • rather sober and subdued
  • lower in activeness, loudness, confidence, intensity, selfishness, and inclination to project blame
  • tendency to play more with girls
  • feminine behavior
  • more responsible, more obedient, less exhibitionistic, less moody, and less active than parallel singletons
  • less close
  • less critical of their sisters than vice versa
  • few friends(Koch 159-160)

fraternal girls (same-sex):

  • more skilled in speech and language (best of all twins)
  • less strongly feminine
  • more vivacious, outgoing
  • less adult centered, less resistant, and less given to fault finding
  • more concerned with family relationships than characterized the identical
  • same feelings about things
  • believed they were treated the same by parents
  • more often the desire to be like their sib
  • more often wanted to play alone
  • more stress about sharing possessions
  • feel less accepted by sib's friends
  • greater distance (Koch 161-162)

Fraternal mixed, girls:

  • Subdued, low in expression of jealousy, exhibitionism, sociability, and aggressiveness
  • Less involved with adults
  • Less syntax errors
  • Told more coherent stories
  • More social contacts
  • Had more own friends
  • Don't think that their parents are impartial
  • Rather rejected their male twin
  • Not masculinized as vice versa
  • More dominant members
  • No rivalry
  • No closeness like in identical (Koch 162-163)

Helen Koch made these observations in 1966 and it questionable, if those characteristics are still applicable or appropriate today, or if it makes sense to generalize character traits like that for the different types of twins at all, or if it is dependent on the individual person. Character traits in twins are very often exaggerated or generalised, which brings about certain stereotypes.


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