A wide variety of animals decorate their outer surface. In a
review paper, Graeme D. Ruxton and Martin Stevens [1] have defined a decorator as:
..an organism that (by means of
specialist behaviour and/or morphology that has been favoured by selection for
that purpose) accumulates and retains environmental material that becomes
attached to the exterior of the decorator.
This definition is a bit complicated as it is designed for
an audience of scientists, but you get the drift. Ruxton and Stevens then give
us some examples, beginning with decorator crabs (below left) that attach all
sorts of materials to hooked hairs present over the body of the animal:
Several studies..have found that
experimentally altering or removing decoration [from decorator crabs] increased
vulnerability to predators.. ..Items used in decoration are often chemically defended
plants or sessile animals, and it seems plausible that predators detect the
crab but actively avoid attacking because of the repellent smell or taste from
the decorations. However, not all decorations provide the animals with chemical
defence, and it is likely that decoration often functions through crypsis via
background matching, masquerade and/or disruption.
Another type of decoration is seen in insects that use
faecal shields, an example being larvae of the tortoise beetle (above right),
where faecal pellets are retained on an extension of the body, so that the
solidified shield provides cover for attack by predators. The shield acts both
in crypsis and as a physical defence [1], isolating the body from potential
attacks; other insects use a covering of faecal material directly on the surface
of the upper body. However, decoration in insects is not confined to the use of faeces:
other components of "backpacks" may be cast skins from moults, or
organic, and mineral, grains obtained from the surrounding environment and
stuck on to the back by secretions, or held there on hairs extending from the
body surface.
Decoration is also used by birds (and I am not including
those, like bower birds, that make collections of bright objects remote from
the animal itself). To quote Ruxton and Stevens [1]:
In birds, a range of species add
substances to their feathers that alter their appearance (termed cosmetic
coloration).. Staining of the feathers with soil has been observed in a number
of large birds.. ..Both sexes [of the rock ptarmigan] sport all-white plumage
at the start of the breeding season, as snow melts this becomes very conspicuous
and females moult to produce feathers that appear to offer good camouflage. By contrast,
males do not moult immediately, but smear their feathers with soil before later
moulting into a brown plumage.
Free-ranging adult bearded
vultures..typically have an orange colour on their underparts, neck and head
conferred by iron oxide-rich soils.. .. Colour tends to be greater in (socially
dominant) females than males and increases progressively from juveniles, to
immatures, to sub-adults to adults.
Ruxton and Stevens conclude their review by saying [1]:
Decorating is a particularly
diverse activity, and (like tool-use) it is difficult to produce an unambiguous
definition that covers all cases effectively.. .. Anti-predator benefits are
most commonly postulated, in contrast to humans where decoration functions
strongly in social interactions.
Their last sentence set me thinking. Unless one believes in
Creation, it is not possible for us to look at the behaviour of our own species
without realising that much of it developed as we evolved so successfully away
from the rest of the Animal Kingdom. In this post, I describe the origins of
human decoration, confining myself to clothes, accessories and make-up, as
these best fit the definition given above.
Humans lack a dense covering of hair over the whole body and
it is likely that our first use of decoration was by draping ourselves in
animal furs that were protective and helped to keep us warm. It could be argued
that this enabled early humans to migrate to regions with cooler climates,
something that was also facilitated by the discovery of fire, but it is
unlikely that animal pelts provided camouflage against predators. Camouflage
coverings are certainly important in providing crypsis in warfare and they form
an important part of the clothing using by contemporary fighters (below),
together with applied face paints. This is analogous to the main use of
decoration used by animals but most of our clothing, in addition to its
functions of keeping us warm and protected, is used in expressing social status,
for mate selection, or for group identity.
Among contemporary costume, the business suit is currently de rigeur for men in many countries and
in many walks of life, with only small changes in the design of a jacket and
trousers. There is status in having a designer label and this is true also of
all clothes, something that conveys both the quality of materials and
tailoring, but also exorbitant cost. The expression of wealth in this way is
important in Western Society, as is the quantity of items in an individual's collection.
Surprisingly, while the business suit represents a work uniform (although casual clothes for men are more varied), women's fashion is
based on variety, and it is considered acutely embarrassing to wear an outfit
that is identical, or too similar, to that worn by someone else at the same social
function. Despite trends in fashion, decoration in women is thus less about
uniformity and more about the uniqueness of the individual. Why?
The answer to this question probably lies ancestrally in
mate selection. Humans do not have a breeding season and mating can occur at
any time through the year. Mate selection is based on genetic factors – the classic
notion of handsome men and beautiful women pairing up – but also on decoration.
Clothes are an important part of this and initial mate selection is often influenced
by clothes, as these convey information about social status and identity, something that is
important if mate selection is for the long-term and where breeding is likely.
Of course, there are more factors than decoration involved in selection, but it
forms an initial signal, with most encounters initiated by men.
In addition to the decoration provided by clothes, there are
also accessories, especially used by women, and we all know individuals with a
shoe and/or handbag addiction. The most similar parallel to animal decorators
comes in jewellery in all its forms. This type of decoration may emphasise
status, as in the integration of precious stones, or be used as a symbol of
lack of availability, as in wedding rings. Similar forms of decoration are
present in many tribal cultures, not just those of the Developed World, and
extend to neck rings, necklaces, nose plugs and rings, ear plugs, earrings and
many other forms. They are not confined to women either, as they are used by
both sexes as indicators of cultures and sub-cultures, something unknown among animals
other than humans.
It is ironic that one design of earrings is based on the activity
of an animal decorator. Larvae of some caddis flies make cases of stones that
are bound together with silk secreted by the insect. This habit has been
utilised by jewellers who give larvae semi-precious stones and wait for each
earring to be produced [2]. It's the only example I can think of where the
activity of one decorator animal is used by another, albeit for a different
purpose.
In addition to clothes and accessories, considerable
attention is given to enhancing the appearance using paints and powders of
various kinds. Use of ochre and ash in face and body colouration is a characteristic
of some "primitive" tribal groups, but make-up in Western Culture is
usually more subtle, with concentration on the face.
As with clothes and accessories, there are variations but, in general, powders
are used to enhance the complexion and to hide blemishes, while various
products are used to decorate the eyes and lips to provide emphasis. Although men
use cosmetics, women are the main users and, as with other forms of decoration,
the underlying message is related to mate selection and/or belonging to a
social group.
Just as humans evolved rapidly, so did our use of decoration.
It now has many forms and is constantly changing, except in tribal cultures and
where national costume, or work customs and uniforms, create an identity. However, we are animals and the
origin of our use of clothing, accessories and make-up lies far back in
evolutionary time.
[1] Graeme D. Ruxton and Martin Stevens (2015) The
evolutionary ecology of decorating behaviour. Biology Letters 11: 20150325.
