Ask A Scientist© Molecular Biology Archive

name        Karl S.
status      other
age         20s

Question -  I read the following question and answer from your web 
site, and I understand the explaination of recapitulating phylogeny, but is it
actually possible for babies to be born with either something
resembling "gill slits" or a "tail"? Possibly flaps of skin or an
elongated tail bone?

Question - Is it true that babies can be born with a
congenital throwback i.e. born with fish gill/s and if so what is it called?
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All mammals seemingly have gill slits in their very early embryo development. 
We call this ontogeny recapitulating phylogeny..where the development of the
individual goes through some of the characteristics of the animals lower in
the evolutionary development.

When we look at early fetal development of various animals we see all having
gill slits, and tails.
Your questions involves very complex answers, but I will address some aspects of 
what you ask.

Yes, there are people born with tail-like fragments or protrusions of the spinal 
column, that are removed or reinserted at birth.  Though I have seen this in 
some medical journal, it is so rare that I have had nurses question the whole idea.  
These "tails" are usually not substantial in structure and certainly do not 
take on a look of a monkey tail, etc.  As a matter of fact, they may not be 
a tail per sa.   I questioned this idea for a long time until I found a friend 
that was born with a very small protrusions of sorts.  Whether it was a tail, 
is probably a matter of semantics.  I do not recall a name for this phenomenon.

If the gill-like slits did remain, the fetus would probably be naturally aborted
at a very young embryonic stage.  The complex feedback system of embryo 
development requires a successful step by step process.  The human genome project
will probably address this or other past characteristics eventually.  Humans have
a tremendous number of introns (I believe in chromosome 20 alone, there are 164
of these-source "Nature" (Dec. 2001 issue ?).It seems that much of our unused 
DNA is coded for our evolutionary past, but this is not clear at this writing.  
It is very clear that we are a product of evolutionary development and we are 
the threshold of understanding all of this better thanks to DNA analysis studies
and related techniques.  Keep your eye out for further developments and 
explanations.

Steve Sample
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