# How many consecutive cell divisions are required to form the adult human body from the single cell zygote?

The preferred question would have been what is the total number of cells in a full term human foetus and how many cell divisions are required to reach that number. However estimates of total cell numbers in foetus could not be found. From the abstract of the July 5, 2013 article published in Annals of Human Biology, the adult human body consists of approximately $3.72 \times 10^{13}$ cells (37.2 Trillion). The question is: what would be the approximate number of cell divisions required to reach that number (Ignoring the fact that different tissues may reach full differentiation at different times)?

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Sounds like just a math problem if you allow that cells dying and different rates of division are not to be accounted for:

$2^N = 40 \times 10^{12}$

$log_2(40 \times 10^{12}) = N$

$N = 45.185$

so 45 or so divisions.

is that what you are looking for?

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I think you want 40T, not 4T. – Amory Sep 17 '13 at 19:12
thanks @Amory - fixed – shigeta Sep 18 '13 at 1:07
@ shigeta - Isn't 45 pretty close to the 'Hayflick limit'? – Ram Manohar M Sep 19 '13 at 15:21
@RamManoharM Supposedly it's between 40-60, so yeah. But if that means anything... – Amory Sep 19 '13 at 16:24
@ Amory - By the time you are 20 (young adult) your have near exhausted the capabilty for cell division (broadly speaking). Just wondering if the loss of Telomere has more important role during development other than merely ushering in senescence. – Ram Manohar M Sep 19 '13 at 16:51