Re: Secular Trend, a sign of human evolution, continues


Interesting. Girls generally (say at 12 years) are much more
emotionally and physically developed than males the same age. This has
been attributed to nutritional factors. However, I think many
scientists are not satisfied with this as just an explanation. The
decline age at menarche in the U.S. is attributed to "secularization".
However, there may be earlier evolutionary processes which preceded the
most current "secularization" which helps to explain the current trend.
Ironically, it deals with a subject Mr. Howard has already posted on
s.b.e. but the general idea is not original to him. In evaluating this
article I'm merely speculating so as to not make any pretenses about
being scientific.

So just how is it possible homosexual males, their brains and evolution
fit in with young menarche? The below following states, "According to
psychologist Louis Berman, homosexual males have low-masculinised brain
('female-like') brains because they have experienced prenatally a lower
brain masculinisation (this is the proximate cause). As a side effect
of the mechanism that creates the male brain, a small percentage of the
male population has a low-masculinised brain, but are otherwise
physically normal males. Many of them become homosexuals. Berman places
this in an evolutionary context. Homosexuality in human males is a
by-product of an evolutionary process that reduced gender differences
and changed a harem based social structure to a heterosexual pair
system (this the ultimate cause). Therefore, homosexuality has no
evolutionary function. Furthermore, the evolutionary transition from
ape to human included a 'premature born' baby, which required a caring
mother. The mother needed a father who not only delivered food, but
cared for the children too. This required the construction of a less
aggressive male brain. Variability in the mechanism that produces this
new male brain causes a small percentage of males with more
'female-like' brains."

Very interesting if Berman is true. Was our earlier evolution based on
a harem based social structure and would have have developmental
maturity occurred so early in females or was it a product of reduced
gender differences that changes a harem based social social to a
heterosexual pair system? Admittedly, it has only been recently 12
year old girls have been able to have children but there must have been
something in our evolutionary past which enabled them to become so
emotionally and physically mature at such a young age. I don't discount
nutritional factors but there has to be more.

I'm less impressed with Berman's idea, "Furthermore, the evolutionary
transition from ape to human included a 'premature born' baby, which
required a caring mother. The mother needed a father who not only
delivered food, but cared for the children too. This required the
construction of a less aggressive male brain. Variability in the
mechanism that produces this new male brain causes a small percentage
of males with more 'female-like' brains." Generally speaking, today's
males still don't care for children too much. The more emotionally and
physically developed females realize this and adopt certain strategies
either by sinking to the level of the male and becoming promiscous or
shopping for the boy with the most accumulated toys.

In my view, it was the shift of moving from a harem social based
structure to a heterosexual pair system which had something to do with
the "secular trend" of young menarche.

Michael Ragland



Homosexual males, their brains and evolution

The Puzzle. Exploring the Evolutionary Puzzle of male homosexuality.
by Louis A. Berman
Godot Press 2003 paperback 583 pages.
illustrated, 2 indexes, references.
reviewed by Gert Korthof, 23 Dec 2003 (updated 8 June 2004)




According to psychologist Louis Berman, homosexual males have
low-masculinised brain ('female-like') brains because they have
experienced prenatally a lower brain masculinisation (this is the
proximate cause). As a side effect of the mechanism that creates the
male brain, a small percentage of the male population has a
low-masculinised brain, but are otherwise physically normal males. Many
of them become homosexuals. Berman places this in an evolutionary
context. Homosexuality in human males is a by-product of an
evolutionary process that reduced gender differences and changed a
harem based social structure to a heterosexual pair system (this the
ultimate cause). Therefore, homosexuality has no evolutionary function.
Furthermore, the evolutionary transition from ape to human included a
'premature born' baby, which required a caring mother. The mother
needed a father who not only delivered food, but cared for the children
too. This required the construction of a less aggressive male brain.
Variability in the mechanism that produces this new male brain causes a
small percentage of males with more 'female-like' brains.














slightly modified
from Berman (2003)
aggressive male gentle male
harem male-female pairs
pronounced sexual dimorphism less pronounced
normal baby 'premature' baby


An attractive feature of Berman's evolutionary explanation is that
it connects previously unconnected facts from psychology, brain
research, endocrinology, embryology, anthropology and evolution to
explain homosexual behaviour. Berman is not a biologist, but if his
theory has anything to say about reality, then it should be able to
generate predictions beyond humans. Humans are confronted with the same
problems all animals are confronted with: surviving, getting food,
getting shelter, getting a mate, getting children, feeding children,
protecting children, educating children, etc. Humans share up to 98% of
their genomes with chimpanzees. Brains have a common ancestor too.
Brains did not fall out of the blue sky. That is what evolution is all
about. Remember Darwin is on the cover. Therefore, it is inevitable to
ask questions such as: Are homosexuality and small sexual dimorphism of
body size in animals correlated? Is the occurrence of homosexuality in
species correlated with low aggression of the males? Have
low-aggression males more offspring? Is it correlated with monogamy?
For the human species, one should collect data about the actual amount
of time fathers invest in their children and not just assume that this
amount has increased. Are human fathers, better fathers than elephant
fathers? In humans, do males still prefer smaller females? Do females
prefer larger males? Male and female chimps have equal body sizes (7),
but chimpanzee males do not generally participate in raising their own
offspring. Chimpanzee, orang-utan and gorilla mothers provide all the
care for their offspring, but according to Bagemihl the males of the
three species show homosexual behaviour (1). Owl monkey fathers carry
their infants from almost immediately after birth and provide most care
(2). Does male homosexuality occur in the Owl monkey with higher
frequency than in species where the mother cares for the children?
>>From this 'quick and dirty' search in the literature, it seems that
there is no simple relation between size dimorphism, male aggression,
paternal care and homosexuality in our closest relatives. It could be
that the human species is unique, but there are always similar
conditions of life in other animals. More data are needed. However, we
know at least what questions we should ask.

It is amazing that Berman missed Bagemihl (1999), but on the other
hand, Berman produced a theory to explain human homosexuality, so
Bagemihl is not extremely relevant for that topic. Bagemihl is good at
collecting facts, but his own alternative non-Darwinian theory is not
very helpful. Berman's theory is very much richer, but he did not apply
it to the animal world. However, from a book that explores the
evolutionary puzzle of homosexuality and features Darwin on the cover,
I had expected more space for animals. But even when one accepts that
the scope is restricted to humans, crucial information is missing: the
lifetime 'reproductive output' of homosexuals compared to
heterosexuals. Berman has a chapter about homosexual men who marry, but
I did not find data about children. Only those data can define the
degree of the Darwinian 'puzzle'. If homosexuals on average were to
have as many children as heterosexuals, there would be no Darwinian
puzzle. It is always important to define your problem exactly before
developing a solution.

Reproduction: positive factors negative factors
heterosexuals high fertility, parental care infertility (intersex,
sex-chromosome disorders), spontaneuous abortion, perinatal death
mother/baby, celibacy, infanticide, sexually transmitted diseases,
incest, long pregnancy and lactation period, menopause
homosexuals bisexual with offspring exclusive homosexuality




The by-product hypothesis
Berman's by-product theory is different from all other theories that
try to explain homosexuality. Not because it is limited to males, but
because it claims that homosexual behaviour has no evolutionary
function. Homosexuality is a by-product of the variable effect of
testosterone on the brain during prenatal development. Berman suggests
that natural selection produced a lowering of the average degree of
masculinisation of the male brain. Due to naturally occurring
variability, the lower end of the normal distribution produces
homosexual males.
This is a pretty sophisticated theory. However, explaining a
feature as a by-product is itself not a sufficient explanation. There
must be an element of inevitability in the by-product to be a plausible
explanation. In general, when a characteristic is useless or harmful
for reproduction, evolution theory predicts it will eventually
disappear. What prevents natural selection from optimising the
mechanism that produces the male brain? Variability can be small or
large and have a symmetric or asymmetric distribution. Why is the
variability so large that it results in up to 4% homosexual males? Why
is natural selection not able to eliminate by-products? The reason
generally is that a compromise is the best what can be achieved (sickle
cell is an example) and the benefits of the solution outweigh the
costs. To evaluate the by-product hypothesis we need to know what the
costs and benefits are of an evolutionary lowering of the average
masculinization of the male brain. It is not impossible to measure the
evolutionary benefits. The benefits must be substantial. For example,
do (heterosexual) men with lower masculinized brains on average have
more children than men with normal or high masculinized brains? and
vica versa? Berman must be interested in this question. If no
difference can be found, Berman's hypothesis seems doubtful.
Intuitively, the 'evolutionary costs' seem clear, but are harder to pin
down. The closest figure what I could find in Berman's book was that
nearly 46% of gay men have heterosexual contacts, which suggests that
homosexual men have at least a 46% reproductive loss compared to
heterosexual men. It seems hard, but not impossible to get better data
than that (via indirect approaches). Nevertheless, Berman is very
pessimistic: "Unfortunately, one could never collect the relevant data,
since homosexuals who marry and have children are, in most cases,
closeted and cannot be identified" (5).
Contrary to Berman's opinion, data about reproduction of
homosexuals do exist. A 1994 survey reported that 67 percent of lesbian
women were mothers, compared with 72 percent of straight women [only a
5% difference]. In Japan 83 percent of homosexual and bisexual men had
offspring. Joan Roughgarden (2004) concludes: "All in all, the data do
not support uncritical acceptance of homosexuality as deleterious" (6).
Therefore, it could be that the evolutionary puzzle of homosexuality is
not as big, as Berman thinks it is.

Are humans unique?
Berman uses the following quote of Frank Beach (1978) twice in his
book: "Human sexuality is about as closely related to mating behavior
of other species as human language is related to animal communication,
and that relationship is distant indeed" and he repeated it again in a
personal communication to me.
It seems that Berman is committed to the view that humans are unique
(3), because his theory depends on it (or the other way around). The
prematurely born baby is a unique human feature he says. However, the
young of kangaroos and other metatherians are extremely immature at
birth. In mammals, bears give birth to very immature babies. Therefore,
humans are not unique in this respect. Following his logic, extra
maternal care is needed as a consequence of the premature birth. This
demands extra paternal support. This demands a gentling of the male
brain. This demands a reduction of sexual dimorphism and a lower
masculinisation of the male brain. As a by-product a low percentage of
homosexual males are born each generation. Yes, all this makes sense,
but this view also creates an (unconscious) bias in Berman's thinking.
If one or more events in this chain of events turned out to be not
unique for humans, Berman must check out what happened in other animals
under similar conditions. This could falsify his hypothesis (4).
However, we need as many similar cases in animals as we can find. One
species is not enough.
Intriguingly, Berman reports animal data that are, I assume,
relevant and support his hypothesis. For example he reports that
monogamous male sparrows tend to have lower testosterone levels than
polygamous sparrow species. Experimentally increasing testosterone
levels stops males helping to feed their young and they start chasing
available females. The experimenters reported a precipitious drop in
the survival rate of the baby sparrows. This extremely interesting
experiment shows that testosterone levels could control monogamy versus
polygamy. Furthermore, it shows the effect on the reproductive output.
And that is what evolution is all about. To test Berman's hypothesis,
it would be extremely interesting to see what the effect of prenatal
testosterone treatment is on sexual behaviour later in life, especially
in mammals (rats, monkeys, apes). This is the way to go (2).
Finally, if behaviour and hormones in sparrows were completely
irrelevant for humans, then why does Berman report about sparrows at
all? If Berman has an elaborated hypothesis about male homosexuality,
then it could be justified to ignore animals. However, if he wants to
explore the evolutionary puzzle of homosexuality, then either go for
it, or remove Darwin from the cover.
In the meantime, Berman's story goes well beyond explaining male
homosexuality. It is a story about how events in our evolutionary past
shaped our brains and behaviour. The book triggered a similar question
as 'The Aquatic Ape Hypothesis', namely: What environmental (and
social) conditions was the human body designed for?



Notes
Bruce Bagemihl (1999) Biological Exuberance, p.276-288. A good
hypothesis makes all the difference. For example Bagemihl reports
weights of male apes, but not of the females, so we cannot deduce size
dimorphism from his data. Further, it is a pity that he did not report
about homosexuality in the unusual and interesting owl monkey.
Good examples of comparative brain and behaviour research can be found
in John Allman (2000) Evolving Brains, Scientific American Library,
p.182. Reviewed in Science, Vol 283, issue 5405, 1121, 19 Feb 1999.
In an email Berman says: "The human species is the only species that
inhabits the entire earth, that can dive to the bottom of the sea, and
fly thousands of feet above the surface of the earth." however, these
are all irrelevant activities. All species are unique by definition,
otherwise they would not be called a species with its own name. The
duck-billed platypus has a unique anatomy and has a unique sense: it
finds insects and mollucs buried in sand by detecting their electrical
activity. Something humans can not do.
please note that an 'exploration' cannot be falsified, whereas a
hypothesis can.
Bernal, personal communication.
Joan Roughgarden (2004) Evolution's Rainbow. Diversity, Gender and
Sexuality in Nature and People, p. 258. [ added: 8 June 2004 ]
This contradicts Rensch's Rule, which says that male size relative to
female size increases with body size of the species. Rensch's rule has
been verified in animals as diverse as arthropods, reptiles, birds and
mammals, including primates. In humans this effect seems to be reduced
by monogamy, which tends to increase female size relative to male size.
See: Malte Andersson and Johan Wallander (2004) Animals behaviour:
Relative size in the mating game, Nature 431, 139-141 [9 Sep 2004].


Further Reading
Here is a useful interview with Louis A. Berman.
Bruce Bagemihl: Biological Exuberance. Animal Homosexuality and Natural
Diversity reviewed on this site.
Gender scientists explore a revolution in evolution by Stephanie
Chasteen. [ February 19, 2002 ].
Carina Dennis (2004) "Brain development: The most important sexual
organ", Nature, 427, 390-392. New evidence suggests that the brain
begins to develop differently in males and females much earlier than
was thought - before sex hormones [testosterone] come into play. Of the
12,000 genes active in the brain, 51 showed different levels of
expression in the brains of male and female mouse embryos before the
gonads had formed. [ 29 January 2004 ].
Sex, drugs and Darwin Letters to the NewScientist magazine about
biologist Roughgarden's story. Reader Margaret Monroe suggests that
oestrogen mimics in every ecosystem on Earth influence the development
of sexual organs, and cause homosexuality. ( However, as we have
learned from Berman, the sex organs are normal, the difference is in
prenatal brain development. Yet, the environmental explanation could be
an alternative for an evolutionary explanation -GK). [9 Feb 2004]
Joan Roughgarden (2004) Evolution's Rainbow. Diversity, Gender, and
Sexuality in Nature and People. Univ. of California Press, hb 474
pages.
The editorial "The complexity of sex. How can a "gay gene" be passed
down the generations?" (p.3) and a short news item "Gay genetics" (p.5)
in the NewScientist, 16 Oct 2004. Simon LeVay proposes a gene for
sexual attraction to men. It makes women to have slightly more children
and men [sons] more likely to be gay. This is a new and original
explanation for the paradox how a gay gene could be inherited at all
and which is also based on data. [ 23 Oct 2004 ]
Gregory Cochran An Evolutionary Look at Human Homosexuality. Cochran
argues that human male homosexuality is caused by a bug that acts on a
specific part of the brain and thereby changes sexual interest. The bug
is not HIV. This hypothesis does not say anything about the cause of
AIDS, because it is not an explanation of AIDS but of homosexual
behaviour. Homosexuality is not caused by HIV (that would be a
circularity), but by some other infectious agent and has probably a
non-sexual transmission. There is no direct evidence for the
hypothesis. 23 Jan 2005


.

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