Reflection reaction
Question: When an animal looks in a mirror, does it realise that it is looking at itself? Which, if any, animals successfully make this connection?
Answer: Experiments in primate self-recognition were done in the 1970s by Gordon Gallup. He anaesthetised chimpanzees, then marked their faces with blobs of nontoxic paint. The chimps were given mirrors to look in when they woke up. They saw the blob in the mirror, touched it and cleaned it off. Apparently orang-utans can also do this, but this behaviour has so far not been recorded in gorillas, monkeys or any other animal apart from humans.
Advertisement
Penny Hawkins
Horsham, West Sussex
Answer: This is still not a completely solved issue. Following Gallup鈥檚 experiments, many researchers found behavioural evidence for self-recognition in apes (chimps, bonobos, gorillas and orang-utans) and maybe in dolphins.
Besides the experiments that involved marking faces, others were devised in which the animal was urged to do something with its hand, which was hidden behind a screen, while being shown a television picture of its hand in reverse. Chimps learn to manage the task by looking at the screen and moving their hand in a trial and error strategy guided by visual feedback. Other tasks investigated whether the animal recognised itself in a video tape image, a photograph, or even its own shadow.
Of course , all these experiments are behavioural tasks which cannot access the mind states of these animals directly and prove if they really do recognise themselves. Some researchers are therefore still sceptical.
Macaques and other less intelligent primates have not yet displayed the self-recognition abilities of apes and humans. And apes that grow up with very limited social contact seem to fail too. Furthermore, developmental psychologists found evidence that self-recognition correlates with empathy. It is possible that both abilities emerge together.
For a good review of the whole subject I can recommend Self-Awareness in Animals and Humans edited by Sue Taylor Parker, Robert W. Mitchell and Maria L. Boccia (Cambridge University Press, 1994).
By the way, human babies normally learn to recognise themselves in the mirror at an age of between 12 and 20 months. Once I sat with a very young girl in front of a mirror, asking her what she could see. 鈥淭hat鈥檚 me,鈥� she told me. I repeatedly insisted that it couldn鈥檛 be her, because she was next to me (I touched her) and not there (I touched the mirror). After a while she said : 鈥淭hat鈥檚 a picture of me.鈥�
Rudy Vaas
Bietigheim-Bissingen, Germany
Answer: A bird regards the reflection as another individual of its own kind and does not realise it is looking at itself.
Several species of territory-defending Australian birds will spend lengthy periods attacking their reflection in, for example, the wing mirror of a vehicle, or a flat chrome hubcap. The magpie lark (Grallina cyanoleuca) is a notorious offender. It is a practice which doesn鈥檛 endear the bird to the motorist, for the mirrored surface becomes smeared with oil from the bird鈥檚 feathers.
The English ornithologist John Gould regarded Australia鈥檚 superb lyrebird (Menura superba) as the shyest and most difficult to approach of all birds. But male lyrebirds are strongly territorial in the breeding season and in the course of research on the species, CSIRO, Australia鈥檚 national research organisation, showed them capable of being captured by using a mirror at the back of the trap.
Syd Curtis
by e-mail, no address supplied
Green policy
Question: In the interests of photosynthetic efficiency, why aren鈥檛 all plants dark green?
Answer: The rate of photosynthesis isn鈥檛 the only factor in deciding how fast plants can grow. Photosynthesis captures carbon, which is only one of many things plants need. Over large areas of the world, plant growth is limited by a lack of water. In other places growth is limited by a lack of nitrogen, phosphorus, or even exotic things like copper, boron or molybdenum. For most plants, most of the time, additional chlorophyll brings no benefit.
Ken Thompson
University of Sheffield
Answer: The assumption in this question seems to be that the more light is absorbed, the greater the rate of photosynthesis鈥攖hat is, instantaneous efficiency, or energy stored per unit of incident light energy, is increased.
However, the fraction of light absorbed is an exponential function of the pigment concentration in a leaf of a given thickness. This means that increasing the fraction of light absorbed from 0.95 to 0.99 of the light that strikes the leaf involves a much greater energy input to synthesise pigments (and associated proteins and lipids) than does increasing the fractional absorption from 0.04 to 0.05.
In determining the efficiency of light use over the life of a leaf these construction costs must be considered as well as the benefits of increased photosynthesis in darker green leaves.
John Raven
University of Dundee
Answer: Plants aren鈥檛 interested in photosynthetic efficiency, but in reproductive efficiency. Many factors, of which light is only one, limit plant growth to maturity and reproduction. Plants need to balance their need to harness light energy with their investment in obtaining nutrients (water, carbon, salts) and setting up defences against pathogens, predators and environmental stresses.
Where in the plant this balance is struck depends on the environment in which it evolved. In arid environments where water determines reproduction, root systems tend to be large and complex to compensate for the scarcity of water. In an environment where a scarcity of light limits reproduction, one would expect to find large, dark-green leaves. Peace lilies, which usually grow under a dark canopy of tropical trees, are an ideal example of such a plant鈥攁nd incidentally, the trait makes them ideal for indoor use.
Piers Mahon
Cambridge University
This week鈥檚 questions
No flakes: How does antidandruff shampoo work?
Eugene
by e-mail, no address supplied
Title claims: It is easier to read titles on book spines on my bookshelf if I incline my head. Why?
Geoff Hyles
Tharwa, ACT
Red or white? Why is red meat red and white meat white? What is the difference between the various animals that makes their flesh differently coloured?
Tom Whiteley
Bath, Somerset