New Scientist – August 17, 2019

17 August 2019 | New Scientist | 23

T

WO things are clear about
human sexual orientation.
First, it is biological; second,
it is complex. Sexual behaviour,
identity, attractions and fantasies
don’t line up neatly. Consistently,
biologists fail to recognise this.
In their 1948 book Sexual
Behavior in the Human Male,
Alfred Kinsey and his collaborators
showed how male sexuality
varies smoothly, from a majority
identifying as completely
heterosexual to a minority
who identify as gay. Men
“do not represent two discrete
populations, heterosexual and
homosexual”, wrote Kinsey. “The
world is not to be divided into
sheep and goats.” He concluded the
same for women five years later.
Biologists often look for factors
related to sexual orientation,
be they genetic, hormonal or in
the brain. It is easier to search
for differences between two
starkly different groups, so the
smooth variation in sexuality
Kinsey described collapses to an
artificial binary: heterosexual
or homosexual, or sometimes
heterosexual or non-heterosexual.
How the boundaries of these
categories are drawn varies wildly.
In some studies, “homosexual”
means anyone who identifies as
mostly or entirely gay or lesbian;
in others, anyone who has had
any type of same-sex experience.
Bisexual people are either lumped
in with gay and lesbian people in
a non-heterosexual category or
excluded for being “inconsistent”.
JOSWomen can also be excluded,

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Comment

Andrew Barron is a

neuroethologist at Macquarie

University in Sydney, Australia

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as female sexuality is often

considered too variable.

Why does this all matter? As

Rebecca Jordan-Young discussed

in her book Brain Storm a decade

ago, by distorting sexual

orientation to fit what we assume

it is, we risk editing out the most

informative data points – and

drawing false conclusions.

As an example, take the recent

book The Goodness Paradox by the

evolutionary psychologist Richard

Wrangham. This is an excellent

account of human cognitive

evolution, but in a section on

homosexuality, Wrangham writes:

“Homosexual men also have

somewhat feminized face shapes

and shorter, lighter bodies than

heterosexual men, most likely

from relatively low exposure to

testosterone in the womb” and

“Homosexual men who take a

strongly male sexual role, for

example, seem less likely to have

had low exposure to prenatal

testosterone than those taking

a more female role.”

Wrangham accepts the findings

are “not always consistent”. But

the underlying science speaks of

small variations between people,

not stark contrasts. A recent study

in Canada (sample size 863) did

find that gay men are slightly

shorter than heterosexual men.

Other studies find no difference.

A recent detailed analysis of the

faces of gay men found a “mosaic

of both masculine and feminine

features”, and that independent

observers rated gay men as

looking more masculine.

As for linking sexual roles in gay

men to developmental hormone

levels, that requires a long line of

causal links through complex,

inconsistent and indirect

evidence. Increasingly, it looks like

the conclusion is too simplistic:

another false dichotomy along

the lines of^ “male” and “female”

brains that ignores immense

variation within groups.

Ultimately, this issue matters

because it isn’t just biologists

who divide the world into gay

and straight. The science of sexual

orientation informs the law and

the societal and self-perception

of minority groups.

The persistence of negative

stereotypes and discrimination

against those of different sexual

orientations is precisely why the

biological sciences must be careful

when studying this area. We need

clear, unbiased answers about

the biological nature of sexual

orientation – even if those answers

are complex. ❚

Sexuality is complex

The desire to collapse human sexual orientation into two neat

categories risks drawing false conclusions, says Andrew Barron