"Humans have not evolved to be monogamous; the survival of the species
depends on diversity."
Fiona Horne, 8 March 2003, The Guardian Weekend

In case you haven’t heard of Fiona Horne, this multi-talented antipodean is a rock
star, journalist, author, model and witch. Seriously. She’s written five books
on witchcraft, including Witchin’: A Handbook for Teen Witches. Like it or not,
what this person says gets published and listened to.

Judge for yourself whether this is a good thing. When asked "How often
do you have sex?" Horne replied, "Every orgasm is a sacred offering
to the universe." When asked if she believed in life after death, she replied,
"The energy that we are has to go somewhere." A witch’s wisdom or
wacky Wicca waffle? I’ll let you be the judge.

Her musings on evolution were in response to the question "Do you believe
in monogamy?" Her answer would seem to suggest that she doesn’t, but in
fact she doesn’t give a direct answer and her reply doesn’t help us decide whether
she means yes or no.

Horne’s reply makes two factual claims: that we have not evolved to be monogamous
and that diversity is essential to the survival of the species. Horne has the
backing of most evolutionary psychologists for the first, since they would agree
that strict monogamy is not the behaviour pattern evolution has favoured. However,
the second part of her claim – that "the survival of the species depends
on diversity" – is something of a non sequitur. There is, after all, no
evidence that the strict practice of monogamy would threaten the "diversity"
required for human survival. The main kind of diversity required for the species
to flourish is a mixing of the gene pool, and this is threatened by excessive
in-breeding, not monogamy.

So the only pertinent point made is that we have not evolved to have a propensity
for monogamy. But even if that is true, the question was about whether Horne believed
in monogamy. Normally we take this to be a question about whether someone thinks
monogamy is a good thing. (Clearly she’s not being asked whether she thinks
monogamy exists.) If this is the question, how can talking about evolution even
begin to answer it?

The problem is that the story of our evolution can only tell us facts (or perhaps
we should say in this case hypotheses) about why humans have certain predilections
for particular types of behaviour. What it can’t do is tell us whether we should
act on these predilections or not. Indeed, morality as normally understood surely
does require us to sometimes go against our evolved predispositions. For example,
many evolutionary psychologists would say that we have evolved to put the welfare
of our close kin above that of strangers. But that would not make it right to
favour a job application from a relative over a better-qualified stranger. What
is right is not necessarily what we are most disposed to do.

The general point is that nothing about what we ought to do necessarily follows
from what we actually do, or have predispositions to do. This is known as the
is/ought gap, and was first expressed in a
famous passage from David Hume’s A Treatise of Human Nature. Hume’s point
is a simple logical one. No statements of values (what "ought" to
be) follow from any premises which simply describe facts (what "is").
If you want to reason from the fact that kicking people causes pain to the conclusion
that you ought not kick people without good reason, you cannot do so unless
you introduce a statement of values, such as "causing pain without good
reason is wrong". You have to put values in to get values out: they are
never simply generated from the facts.

The debate over the is/ought gap has got quite sophisticated and many philosophers
argue that the gap is not unbridgeable. However, even if the gap can be bridged
it needs some clever reasoning and demonstration for it to be done. What cannot
be justified is a leap from facts to values with no demonstration of how this
can happen. And certainly to answer a question about values with a stark statement
of fact, as Ms Horne did, is not to answer the question at all, no matter what
the respondent thinks.