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<DIV>I concur with Lorraine! </DIV>
<DIV>
<DIV>
<DIV>Another thing that might be helpful, for some, is to create a 'Premise
Checker' folder that Frank's webmails go directly into. (On Outlook Express this
can be done by creating a new message rule.) While, of course, it doesn't change
the amount of emails, it might provide a sense of
order... </DIV>
<DIV> </DIV></DIV></DIV>
<DIV style="FONT: 10pt arial">----- Original Message -----
<DIV style="BACKGROUND: #e4e4e4; font-color: black"><B>From:</B> <A
title=andrewsa@newpaltz.edu href="mailto:andrewsa@newpaltz.edu">Alice
Andrews</A> </DIV>
<DIV><B>To:</B> <A title=checker@panix.com
href="mailto:checker@panix.com">Premise Checker</A> </DIV>
<DIV><B>Sent:</B> Sunday, April 24, 2005 7:39 AM</DIV>
<DIV><B>Subject:</B> your e-straw poll</DIV></DIV>
<DIV><BR></DIV>
<DIV>
<DIV>
<DIV>Hi Frank,</DIV>
<DIV>Whatever you end up doing will be just fine w/<EM>me</EM>...However, I
happen (also) to like having the articles in the body of the text (in addition
to a link), as you've been doing...Some of them (and not just the science
ones) are wonderful and have helped me tremendously in my teaching, writing, and
research. So (more) thanks! Have you sent this one in, btw?</DIV>
<DIV>
<DIV>All best,</DIV>
<DIV>Alice</DIV>
<DIV> </DIV>
<DIV> </DIV></DIV>
<DIV> </DIV>
<DIV>
<H2> </H2>
<H2><A
href="http://www.nybooks.com/articles/17973">http://www.nybooks.com/articles/17973</A></H2>
<H2><EM>The New York Review of Books</EM>:</H2>
<H2>
<H2>Vive la Différence!</H2>
<H4>By <A href="http://www.nybooks.com/authors/9368">H. Allen Orr</A></H4>
<H5 class=reviewed-title><A class=bn-link
title="More about this book from Barnes & Noble"
href="http://service.bfast.com/bfast/click?bfmid=2181&sourceid=41397204&bfpid=0393058964"
target=_blank>Adam's Curse: A Future Without Men</A></H5>
<H5 class=reviewed-author><FONT size=3>by Bryan Sykes</FONT></H5>
<P class=reviewed-info><FONT size=3>Norton, 320 pp., $25.95; $15.95
(paper)</FONT></P>
<H5 class=reviewed-title><A class=bn-link
title="More about this book from Barnes & Noble"
href="http://service.bfast.com/bfast/click?bfmid=2181&sourceid=41397204&bfpid=0618565612"
target=_blank><FONT size=3>Y: The Descent of Men</FONT></A></H5>
<H5 class=reviewed-author><FONT size=3>by Steve Jones</FONT></H5>
<P class=reviewed-info><FONT size=3>Houghton Mifflin, 252 pp., $25.00</FONT></P>
<H5 class=reviewed-title><A class=bn-link
title="More about this book from Barnes & Noble"
href="http://service.bfast.com/bfast/click?bfmid=2181&sourceid=41397204&bfpid=0674016211"
target=_blank><FONT size=3>The X in Sex: How the X Chromosome Controls Our
Lives</FONT></A></H5>
<H5 class=reviewed-author><FONT size=3>By David Bainbridge</FONT></H5>
<P class=reviewed-info><FONT size=3>Harvard University Press, 205 pp., $22.95;
$14.95 (paper)</FONT></P>
<P><FONT size=3>The human genome is made up of forty-six chromosomes, the
rod-like structures that reside in the nucleus of every cell. These chromosomes
carry all of our genes, which, in turn, are made of DNA. Two of these
chromosomes, called the X and the Y, are different from the rest: they are "sex
chromosomes." Men carry one X and one Y chromosome, while women carry two X
chromosomes. All the obvious physical differences between the sexes ultimately
spring from this humble difference in chromosomal constitution. </FONT></P>
<P><FONT size=3>During the last few years, real progress has been made in our
understanding of the sex chromosomes and we now know much more about our X and Y
than we did a mere decade ago. In 2003, for example, essentially the entire
stretch of DNA carried on the human Y chromosome was decoded, revealing the
number and, in many cases, identity of the genes that make up this seat of
maleness. More important, owing to a breakthrough that occurred in the early
Nineties, biologists now understand just how sex is decided in human
beings—geneticists identified the master "switch gene" that determines whether
an embryo will develop into a male or a female. </FONT></P>
<P><FONT size=3>These discoveries might seem surprisingly recent. In view of the
confident pronouncements in the medical press about all things having to do with
sex and gender (homosexuality, for example, was said to be genetically
determined), you'd be forgiven for assuming that the biology of how a human
being becomes a boy or a girl has long been understood. To be fair, though,
there were good reasons for the slow progress. How sex is determined represents
a rare problem in which the study of simpler organisms like fruit flies led
biologists astray. Sex determination in human beings specifically and in mammals
generally doesn't work the way it does in most of the species that geneticists
like to study. Moreover, genetic studies in human beings are simply harder to
perform than those in species like the fruit fly: a generation is more like two
decades than two weeks, and we can't dictate who mates with whom, an ethical
constraint that doesn't arise with flies. </FONT></P>
<P><FONT size=3>Although the three books discussed here cover much of the same
ground, one stands out from the rest. Bryan Sykes's <I>Adam's Curse</I> is both
far more ambitious, and controversial, than Steve Jones's or David Bainbridge's
book. Sykes, a professor of genetics at Oxford University and author of the
best-selling <I>The Seven Daughters of Eve</I>, sounds loud alarms about an
impending biological crisis involving the Y chromosome. He also makes bold
sociobiological claims about the effect of the Y chromosome on our lives.
Because Sykes is a leading researcher in the study of sex chromosomes (not to
mention a science adviser to the House of Commons), his pronouncements merit
special attention. </FONT></P>
<H3><FONT size=3>1.</FONT></H3>
<P><FONT size=3>Sykes begins his book with the discovery of the master gene that
decides sex in human beings. For decades, biologists understood that human
beings have so-called Y-dominant sex determination. Roughly speaking, if you
carry a Y chromosome, you're a male, while if you don't carry a Y chromosome,
you're a female. As a result, rare individuals born with two X's <I>and</I> a Y
are boys, while rare individuals born with one X and no Y are girls. There is
therefore something on the Y, not the X, that decides sex. Identifying this
something, however, proved extraordinarily difficult.</FONT></P>
<P><FONT size=3>As often occurs in human genetics, the key breakthrough involved
extremely rare exceptions to the above rules. In the late 1980s, several people
were found whose sex appeared not to match their sex chromosomes. Some were
patients who had an X and a Y chromosome and yet were female. Careful study
revealed that these patients' Y chromosomes were incomplete—they lacked a small,
defined piece of the normal chromosome. Others were patients who carried two X
chromosomes and (apparently) no Y and yet were male. Careful study revealed that
these patients carried a very small piece of the Y chromosome, typically too
small to be seen under a microscope. Remarkably, the small bit of the Y missing
from the female patients roughly corresponded to the small piece present in the
male patients. This proved that sex does not depend on the presence or absence
of an entire Y chromosome and further suggested that whatever gene or genes
decide sex reside in the relevant small region of the Y. The race to locate the
human "sex determination gene" was on.</FONT></P>
<P><FONT size=3>As Sykes recounts it, the race was filled with false starts. In
1987, a research team at the Whitehead Institute near Boston announced the
discovery of ZFY, a gene that sits in the appropriate part of the Y and that had
certain molecular features that, the team believed, made it a strong candidate
for the sex gene in humans. Soon, however, the ZFY story unraveled (for one
thing, ZFY turned out to also sit on the X chromosome, which made little sense)
and the race, briefly suspended, began anew.</FONT></P>
<P><FONT size=3>In the 1990s, another research team led by Peter Goodfellow and
Robin Lovell-Badge at the Human Molecular Genetics Laboratory and National
Institute for Medical Research in London identified another Y chromosome gene
which they confidently named SRY, for Sex Determining Region of the Y
chromosome. Their confidence was, in this case, well placed. During the
following year, the same team performed a critical experiment proving that SRY
does in fact determine sex in mammals. Injecting a copy of the SRY gene into
mouse eggs, the team produced a mouse that carried two X chromosomes and SRY—and
it was male. SRY was able, therefore, to force an embryo otherwise destined to
become female to develop instead as male. As Sykes recalls, the "star mouse,
swinging on a stick and sporting enormous testicles to prove the point, made the
cover of the edition of <I>Nature</I>" that announced the discovery of
SRY.</FONT></P><FONT size=3>
<HR class=section-break>
</FONT>
<P class=initial><FONT size=3>Although many details of how SRY works remain
uncertain, some things are clear: SRY is a special kind of gene that has the
power to switch other genes on or off. Genes exist in two states: on, in which
they make a protein product (say, hemoglobin for your red blood cells), or off,
in which they sit idly, making no protein product. SRY can switch some genes
from one of these states to the other. No one imagines, therefore, that the many
physical features that distinguish boys from girls—penises not vaginas, testes
not ovaries, and so on—reflect the immediate effects of SRY alone. Rather, SRY
sits at the top of a genetic cascade: if present, it switches on a set of other
genes, some of which may in turn switch on yet other genes, and so on. (These
other genes do not reside on the Y, but are scattered throughout the genome.)
The cumulative effect of all this genetic switching is the development of
testes; and the testes in turn produce hormones that then complete the
development of a male anatomy. As this description implies, it is also now clear
that the original state of a human embryo is female. It takes active work by SRY
to divert the normal path of development from female to male, a process that, in
human beings, starts when the fetus is seven weeks old.</FONT></P>
<P><FONT size=3>Sykes gives an excellent account of the subtleties of human sex
determination. Indeed he skillfully leads us through a number of other topics in
human genetics, including his own research on the use of Y chromosome
"fingerprinting" to reconstruct the movement of men throughout history.
Contemporary Polynesian men, for example, often carry Y chromosomes whose DNA
clearly derives from Europe, a vestige of the conjugal visits of European
sailors in the age of exploration. And an astonishing number of men who live
within the borders of the old Mongol Empire carry what is genetically the same Y
chromosome. Sykes suggests that this extraordinarily popular Y may descend from
Genghis Khan himself, who typically slaughtered the men he conquered and bedded
the women he vanquished throughout much of Central Asia. </FONT></P>
<P><FONT size=3>Fascinating as all this is, though, it turns out to be
preliminary, a long preamble to Sykes's real purpose: to warn the world of his
most important discovery—that human beings face an immense genetic disaster. And
here Sykes's book takes a sharp turn for the worse.</FONT></P>
<H3><FONT size=3>2.</FONT></H3>
<P><FONT size=3>Although Sykes doesn't describe this impending disaster until
fairly late in his book, the subtitle to <I>Adam's Curse</I> gives it right
away: we face a future without men. Sykes is convinced that the male of the
species is doomed. Unless something is done—and soon— men face an "inevitable
eventual extinction." You won't be surprised to learn that the alleged causes of
this crisis reside in the Y chromosome. Sykes's publishers have, predictably,
latched on to this dire news and the cover of his book speaks in ominous tones
of the certain extinction of half of humanity. Also not surprisingly, the press
has played along, with pieces in <I>The New York Times</I> and <I>The
Guardian</I> warning that men may be a thing of the past.</FONT><A
name=fnr1></A><SUP><A href="http://www.nybooks.com/articles/17973#fn1"><FONT
size=3>[1]</FONT></A></SUP><FONT size=3> </FONT></P>
<P><FONT size=3>Sykes's case for the extinction of men hinges on an unusual
problem plaguing many genes on the Y chromosome—they tend to pick up
debilitating mutations and to ultimately degenerate into genetic junk. A couple
of hundred million years ago or so, the X and Y were a pair of perfectly
ordinary chromosomes that each carried a full complement of the same thousand
genes. Since then, however, the Y has been slowly degenerating. As a result,
while the human X still carries its thousand genes, the Y carries only about a
hundred. Sykes believes that the genes that remain on the Y—including SRY as
well as others required for the fertility of men—will also degenerate. The
disastrous consequence, he says, will be the disappearance of fertile males.
(Sykes sometimes says that males will become sterile, while at other times he
suggests they'll disappear. Genetically, at least, the difference doesn't make a
difference: if all males are sterile, they may as well not be there.)
</FONT></P>
<P><FONT size=3>Sykes even tries to calculate when disaster will strike. He
concludes that, given the high rate of mutation on the Y, nearly all men will be
almost completely sterile in about 125,000 years. In the meantime, male
fertility will steadily fall. Adam's curse is, then, a rather serious affair.
Not surprisingly, Sykes suggests some ways to avert this looming disaster. He
seems most serious about using biotechnological methods to relocate Y chromosome
genes, moving them to kinder, gentler chromosomes, where their continued
existence is presumably assured. (Such a transfer is, in principle, possible,
though some technical hurdles would have to be cleared.) </FONT></P><FONT
size=3>
<HR class=section-break>
</FONT>
<P class=initial><FONT size=3>I'm afraid that this is all just silly. There are
several related theories of why most genes on the Y chromosome degenerate and
none of them predicts that men will become extinct. To see why not, we need to
understand why Y chromosomes degenerate in the first place. All theories of Y
degeneration (full disclosure: one of them is mine) hinge on an unusual feature
of the Y: it doesn't "recombine." Recall that half your chromosomes come from
your mother and half from your father. When you make sperm or eggs, each of your
chromosomes from your mother pairs up with the corresponding one from your
father. During this process, the two chromosomes often swap genetic material, an
event called recombination. Consequently, any chromosome entering your sperm or
egg likely carries some genes from your mother and others from your father.
Oddly, though, the Y doesn't play this game: while all other chromosomes
(including the X) recombine, the Y does not.</FONT><A name=fnr2></A><SUP><A
href="http://www.nybooks.com/articles/17973#fn2"><FONT
size=3>[2]</FONT></A></SUP><FONT size=3> </FONT></P>
<P><FONT size=3>This is important because recombination, it turns out, makes it
easy for natural selection to get rid of bad mutations. Put conversely, natural
selection is somewhat compromised when dealing with chromosomes that don't
recombine. All our theories of population genetics thus predict that the Y will
slowly but surely accumulate mutations that have slightly bad effects. But the
key point is this: the process I have described will not spiral out of control,
yielding sterile or absent men, for two reasons. The first is that the
evolutionary forces that cause genes on the Y chromosome to degenerate turn out
to be very weak; that's why it's taken hundreds of millions of years for our Y
to fall into its current state of disrepair. In contrast, the evolutionary
forces that maintain male fertility—and that even maintain a 50:50 ratio of
males to females in populations—are very strong. The latter, strong forces,
overcome the former, weak ones, and males neither become sterile nor disappear.
</FONT></P>
<P><FONT size=3>Second, not all genes on the Y chromosome are created equal.
Some, indeed the great majority, originally resided on both the Y <I>and</I> X
chromosomes. Natural selection will often tolerate loss of this kind of gene
from the Y since there's a "backup" copy on the X that can still perform the
gene's functions. Other genes, though, now exist <I>only</I> on the Y. Natural
selection will most assuredly not tolerate the loss of this kind of gene since
no backup copy sits on the X. The critical point is that most of the male
fertility genes now residing on the human Y exist only on that chromosome and
there's no way that selection will allow their loss.</FONT></P>
<P><FONT size=3>Sykes's calculation suggests otherwise because it's wrong. He
seems to assume that Y chromosomes carrying mutations that partially sterilize
men will get passed on to future generations as often as normal, unmutated
chromosomes. But they won't—that's what it means to be partially sterile. This
misstep leads Sykes astray. There are simply no sound evolutionary grounds to
support his sensational claims of the extinction of men.</FONT><A
name=fnr3></A><SUP><A href="http://www.nybooks.com/articles/17973#fn3"><FONT
size=3>[3]</FONT></A></SUP><FONT size=3> </FONT></P>
<P><FONT size=3>This is not to say that Y chromosomes can't be lost from a
species. They can and sometimes are. But it is to say that the Y can disappear
only after it's become dispensable, i.e., only after genetic changes take place
that render Y-less males healthy and fertile. Sykes gets this logic backward.
Telling the story of a rodent called the mole vole that's lost its Y, he marvels
that these lucky voles made the genetic changes needed to avoid male extinction
"only just in time" before their Y disappeared. But this is like saying that you
got out of your clothes only just in time before they were thrown in the wash.
In reality, the later event is contingent on the earlier. </FONT></P>
<P><FONT size=3>The bottom line is that Sykes's alarmist talk of the extinction
of men is just that—alarmist—and I wouldn't lose too much sleep over the
possibility. And I certainly wouldn't give much thought (much less funding) to
his technological fix to this nonproblem. There are enough real problems out
there.</FONT></P>
<H3><FONT size=3>3.</FONT></H3>
<P><FONT size=3>Talk of sex chromosomes and of single genes that determine sex
naturally raises the specter of genetic determinism. Are certain behaviors and
thoughts fundamentally male and others essentially female? To just what extent
does recent biological research support the notion that genes determine our
identity, sexual or otherwise? </FONT></P>
<P><FONT size=3>The answer to this question depends entirely on the particular
trait or character under discussion. If the character of interest is having
testes or not, we are confronted with a biological determinism of the first
magnitude. Whether an embryo develops testes depends essentially entirely on its
genes; indeed you'd be hard pressed to find anything more genetically hardwired.
If this brand of biological determinism alarms you, you are destined to be
alarmed.</FONT></P>
<P><FONT size=3>But things are considerably less clear if the trait of interest
is, say, aggressiveness, or a curiosity about genes. Unfortunately, this (not so
subtle) distinction is often lost on Sykes. Sociobiological claims of an almost
unbelievably unnuanced sort run throughout <I>Adam's Curse</I>. Sykes's chief
claim is that the Y chromosome causes its bearers to do crazy things. Sykes
tells his readers that men, violent and sex-crazed, are "driven on by the lash
of their Y chromosomes," and that the Y has "claimed the power to force us, men
and women alike, to submit...to its will." Indeed it soon appears that the Y is
legally liable for war, the subjugation of women, and empire
building:</FONT></P>
<BLOCKQUOTE><FONT size=3>Driven on and on by the crazed ambition of the
Y-chromosome to multiply without limit, wars began to enable men to annex
adjacent lands and enslave their women. Nothing must stand in the way of the
Y-chromosome. Wars, slavery, empires—all ultimately coalesce on that one mad
pursuit. </FONT></BLOCKQUOTE>
<P><FONT size=3>In places Sykes is so overcome by the power of the Y chromosome
that he passes from breathless exaggeration to patent absurdity. In a remarkable
passage, he argues that Genghis Khan's Y chromosome was so successful that it's
hard to know who was in charge: </FONT></P>
<BLOCKQUOTE><FONT size=3>Is the Khan chromosome's achievement owing to the
sexual exploits and military conquests of the Mongol emperor? Or was the Great
Khan himself driven to success in war, and in bed, by the ambition of his Y
chromosome? </FONT></BLOCKQUOTE>
<P><FONT size=3>Since Sykes tells us—and on the previous page—that 16 million
men now carry the Khan Y chromosome, the answer seems painfully clear: if the Y
is in charge, the world would now have 16 million Genghis Khans on its
hands.</FONT></P>
<P><FONT size=3>Although Sykes's excesses might be excused as the inevitable
hyperbole of a popularizer, their cumulative effect is serious and does, I
think, do real damage: it's hard to believe that a biologically naive reader
could walk away from <I>Adam's Curse</I> with a sensible view of the connection
between genes and behavior.</FONT></P><FONT size=3>
<HR class=section-break>
</FONT>
<P class=initial><FONT size=3>In any case, Steve Jones's <I>Y</I> and David
Bainbridge's <I>The X in Sex</I> prove that popular books on human
genetics—indeed on human sex chromosomes—need not trade in sociobiological
excess. Sykes, Jones, and Bainbridge cover much of the same ground —all recount
the discovery of SRY, discuss the role of hormones in sexual development, and
describe Darwin's theory of sexual selection. But their positions on genetic
determinism differ profoundly. </FONT></P>
<P><FONT size=3>Jones, professor of genetics at University College, London, and
the author of <I>The Language of Genes</I> and <I>Darwin's Ghost</I>, offers his
latest book as an update of Darwin's 1871 classic <I>The Descent of Man</I>.
Although Darwin was more of a hereditarian than many evolutionists like to
admit, Jones himself turns out to be very cautious about attributing human
behavior to genes. While he obviously understands that carrying the Y chromosome
or not means that men and women will express at least some different genes, his
treatment of the consequences of this difference is far more measured than
Sykes's. Indeed Jones is, in places, explicitly anti-sociobiological. He reminds
us, for example, that the Y chromosome has all too often served as "a useful
alibi for man's excesses" and emphasizes that </FONT></P>
<BLOCKQUOTE><FONT size=3>manhood tells a social tale as much as one written in
nucleic acids [DNA] and must, with all that it implies, be constructed. Once
the foundations of the male state are laid, what rises from them has little to
do with DNA. </FONT></BLOCKQUOTE>
<P><FONT size=3>Such sentiments are all too rarely expressed in popular writing
about human evolution or genetics and it is to Jones's credit that his smart and
informative book bucks the trend.</FONT></P>
<P><FONT size=3>For his part, Bainbridge, a lecturer at the Royal Veterinary
College, London, and author of <I>Making Babies: The Science of Pregnancy</I>,
essentially eschews the entire controversy over evolutionary psychology. He
sticks instead to hard science. Although Bainbridge is given to talking about
how chromosomes "control our lives" or "become our dictator," he focuses almost
entirely on the role of chromosomes in human disease, not in human cognition,
emotion, or behavior. And when it comes to disease, there is, of course, little
doubt that chromosomes do often control our lives. </FONT></P>
<P><FONT size=3>Bainbridge's book is largely devoted to the X chromosome, not
the Y. He spends much of his time on "sex-linked" conditions that affect men
more than women; these range from annoyances like baldness to devastating
diseases like muscular dystrophy.</FONT><A name=fnr4></A><SUP><A
href="http://www.nybooks.com/articles/17973#fn4"><FONT
size=3>[4]</FONT></A></SUP><FONT size=3> Bainbridge also devotes many
fascinating pages to complex ailments like autoimmune disease that, for reasons
which remain unclear, disproportionately afflict women. (Hashimoto's
thyroiditis, for instance—a leading cause of underactive thyroids—affects fifty
times more women than men.) </FONT></P>
<P><FONT size=3>But Bainbridge's chief concern is with the biology of human sex
determination and with the many ways in which it can, and does, go wrong. In the
end, his message is that while human beings obviously come in two predominant
sexes, both cultural and biological forces give rise to a surprisingly
"continuous spectrum of gender." While Bainbridge makes it fairly clear that he
wouldn't be surprised if genes sometimes cause men and women to act or think
differently, he's largely silent about the nature and extent of any such
differences. While it's hard to know for sure, I suspect that this silence
reflects the cautious neutrality of a sensible scientist confronted with mixed
data and mountains of speculation.</FONT></P>
<P><FONT size=3>For the truth is, of course, that we have little idea how much
of the variation in human behavior—whether between the sexes or within them—is
caused by genes. While I could defend this claim by pointing to a body of
technical literature filled with conflicting assertions about the heritability
of human behavior, there's no need for such a thing. The same point is made
(albeit inadvertently) by the three books under review. Although all are written
by smart male British biologists who read essentially the same scientific
literature and who live and work within a hundred miles of each other, their
views on the role of genes in human behavior are widely divergent, ranging from
enthusiastic endorsement to considerable skepticism to apparent neutrality. This
lack of consensus speaks for itself.</FONT></P>
<H5><FONT size=3>Notes</FONT></H5>
<P><A name=fn1></A><SUP><A
href="http://www.nybooks.com/articles/17973#fnr1"><FONT
size=3>[1]</FONT></A></SUP><FONT size=3> See Claudia Dreifus, "Is Genghis Khan
an Ancestor? Mr. DNA Knows," <I>The New York Times</I>, June 8, 2004. See also
Bryan Sykes, "Do We Need Men?" <I>The Guardian</I>, August 28, 2003.</FONT></P>
<P><A name=fn2></A><SUP><A
href="http://www.nybooks.com/articles/17973#fnr2"><FONT
size=3>[2]</FONT></A></SUP><FONT size=3> This is almost, but not exactly, true.
Tiny regions of the Y do in fact recombine with the X. I ignore these
"pseudoautosomal regions" here, as they make up a small part of the Y chromosome
and play no role in what follows.</FONT></P>
<P><A name=fn3></A><SUP><A
href="http://www.nybooks.com/articles/17973#fnr3"><FONT
size=3>[3]</FONT></A></SUP><FONT size=3> For a review of how and why Y
chromosomes fall apart, see B. Charlesworth and D. Charlesworth, "The
Degeneration of Y Chromosomes," <I>Pro-ceedings of the Royal Society of
London</I>, Vol. 355 (2000), pp. 1563–1572. </FONT></P>
<P><A name=fn4></A><SUP><A
href="http://www.nybooks.com/articles/17973#fnr4"><FONT
size=3>[4]</FONT></A></SUP><FONT size=3> Because mutations on the X chromosome,
not the Y, cause these conditions, it might not be obvious why they typically
affect men, not women. The reason is that women, who carry two X chromosomes,
can partly "mask" the effects of a mutated X with their other (and usually
unmutated) X chromosome. Men, who have a single X, can't mask mutations in this
way.<BR>This explanation, however, gets complicated in two ways. First, women
randomly "inactivate" (turn off) one of their X chromosomes within each of their
cells. So women mask the bad effects of mutated X chromosomes partly because
those cells that happen to leave the good X turned on can "cover" for those
cells that leave the bad X turned on. Second, recent work shows that this
traditional account is somewhat incomplete. It turns out that, while <I>most</I>
of the genes on one of a woman's X's are turned off, 15 percent are not. The
result is that women, within their cells, express two copies of these X
chromosomal genes while men express one. (See L. Carrell and H.F. Willard,
"X-Inactivation Profile Reveals Extensive Variability in X-Linked Gene
Expression in Females," <I>Nature</I>, Vol. 434, 2005, pp.
400–404.)</FONT></P></H2></DIV></DIV>
<DIV><BR> </DIV></DIV>
<DIV><BR>********************************************************************************************<BR> <BR>Once
again, for some reason I don't understand, several people have sent emails that
I have absolutely not received. So, if you have sent me an email to which I have
not responded at all after an appropriate time (I usually respond within several
days but sometimes minutes!), there's a good chance I didn't receive it; and you
might want to send again! <BR>Thanks!</DIV>
<DIV> </DIV>
<DIV>Alice Andrews<BR>Department of Psychology<BR>State University of New York
at New Paltz<BR>75 S. Manheim Blvd<BR>New Paltz, NY 12561<BR>845.257.3602<BR><A
href="mailto:andrewsa@newpaltz.edu">andrewsa@newpaltz.edu</A><BR><A
href="http://www.newpaltz.edu/~andrewsa">www.newpaltz.edu/~andrewsa</A><BR><A
href="http://www.entelechyjournal.com">www.entelechyjournal.com</A></DIV></BODY></HTML>