Twinning rates

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Gary Steinman is the researcher who published the findings that diet may modify fraternal twinning rates. I just listened to him giving an interview on the radio, and he made the following points:

  • Fraternal twinning rate seems to track basal levels of IGF
  • Basal levels of IGF vary across populations, Sub-Saharan Africans have the highest rates, Asians the least, and twinning rates follow this trend
  • When Yoruba move from the countryside to the city their twinning rates drop to the European level, while Japanese American twinning rates converge with white American twinning rates as opposed to Japanese twinning rates


  1. Not quite a comment about Twinning Rates, but I did come across this interesting twin fact and was wondering how this could be. It seems identical twins Jeremy and Josh Sowers are both major league prospects as pitchers. The odd thing is one is a lefty and the other a righty. 
    what could have caused identical twins to differ in this somewhat crucial respect.

  2. VERY interesting.  
    IGF deficiency also GREATLY extends life expectancy in most organisms.  
    By the way, identical twins frequently differ in handedness.

  3. steve, a left handed friend has told me of the existence of mirror twins: 
    this could explain the phenomena of twins with opposite handedness, but i imagine it would cause medical problems that would prevent at least one from becomming a MLB pitcher

  4. Identical twins can mirror in varying degrees. My identical twins mirrored in teething. If twin A was getting an upper right canine, twin B was getting an upper left canine at the same time. It held true for each tooth. Bizarre, yet neat. The crowns of their hair also appear on opposite sides, and it seems so far that one favors the right hand, and the other favors the left. It’ll be interesting to see if the mirroring happens with anything else.

  5. It’ll be interesting to see if the mirroring happens with anything else 
    The test for foot dominance is the answer to the question, “Which foot do you favor when you kick a ball?” 
    The test for ear dominance is, “Which ear do you favor when you put an ear to a door?” 
    Here is the test for eye dominance: 

  6. Here is the test for eye dominance 
    Wow, I just discovered that I’m left-eye dominant. I’m right-dominant in everything else (as far as I know). Now I understand some things that I’ve observed since childhood but never understood! Thanks, Tex!