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From: rim@csadfa.cs.adfa.oz.au (Bob McKay)
Newsgroups: sci.bio
Subject: Re: Can unrelated twins exist (again)
Message-ID: <1796@ccadfa.adfa.oz.au>
Date: 6 Aug 90 02:46:21 GMT
References: <15289@reed.UUCP>
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From article <15289@reed.UUCP>, by buckley@reed.UUCP (Ken Buckley):
> To my intense surprise, the answer is a definitive no! Using some of the
> responses I got, a friend and I made the following conservative(!)
> estimate: approximately 10^166 humans would be needed to make this an event
(unrelated twins arising by chance)
> with even a remote chance of occurring.
Could we have more details of the computations involved? The reason I'm asking
is that I'm guessing you needed to assume independence of distribution of 
individual genes - presumably on the basis that unrelated humans would have
independently distributed genes. But when we are talking about such 
astronomical numbers, it's probably not a valid assumption: for example, there
may be synergistic effects on the evolutionary fitness arising from 
particular combinations of genes. Normally, we can afford to ignore these
because the effects are likely to be small. But when we're dealing with
numbers like 10^166, all bets are off.
Bob McKay		   Phone:	+61 6 268 8169	    fax: +61 6 268 8581
Dept. Computer Science		ACSNET,CSNET:	rim@csadfa.cs.adfa.oz
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Canberra ACT 2600 AUSTRALIA	ARPA:	rim%csadfa.cs.adfa.oz@uunet.uu.net