But do chimps look forward to sex?

Our closest extant relatives have received a fair bit of attention in the past few days, with the publication of two new studies which have been picked up by numerous news outlets.

First came the study by Fraser et al, which shows that chimps, like humans, console each other with physical contact following bouts of aggression. This was found to occur more often when a fight between two chimps was not followed by reconciliation, and was more likely to take place between individuals that share a close relationship.

This study was quickly followed by that of Townsend et al, who show that female chimps alter the sounds they make during sex according to the status of the male they are copulating with, and to which other chimps are within earshot: females were found to call out when copulating with a high-ranking male, to signal to other males of similar status that they are receptive, but they suppressed their calls when other females were nearby, thereby minimizing the risks that go with competition for mating partners. Altering the sounds they make during sex therefore appears to be a strategy for females to find as many mating partners as possible behind other females' backs. (Here's a recording of the copulation calls of a female chimp.)

Both papers provide further evidence that the social lives of chimps are far more complex than we previously thought. It's all very interesting stuff, and both papers deserve the attention they have received from the media. The second story in particular is one that the tabloids can have a field day over: the Daily Mail, for example, ran the story with the headline "Why female chimps are so hungry for love...and only noisy in bed with weaker males".

There is, however, a third new study, which also involves chimps. It is equally fascinating, but has not been so widely publicized; I discuss it below.

This latest study, which is published online in the journal Animal Cognition. investigated whether or not two chimps and orangutans have the ability to plan for the future. This is a demanding skill; it requires self-control, as it involves suppressing immediate needs in favour of a reward which will be received at a later time. It also requires the ability to construct mental representations of possible future events.

Because it requires such complex thought processes, the ability to think ahead has been considered to be unique to humans. Last year, however, researchers from the University of Cambridge showed that scrub jays can anticipate and plan for their future needs, and now, Mathias and Helena Osvath of Lunds University in Sweden show that chimps and orangutans can too.

First, two female chimps and one male orangutan were presented with a wooden box measuring 19 x 15 36cm, containing a transparent bottle filled with a fruit soup reward. One of the keepers demonstrated how the soup could be sucked up through a plastic hose placed through the hole in the top of the box and into the bottle. The hose was then given to each of the apes in turn; all of them spontaneously re-inserted it into the box to retrieve the soup reward. This training was carried out only once, to exclude the possibility of learning by association, which requires several pairings of the hose and the soup.

Later on, the wooden box was placed in a different room that did not contain any tools. The apes were taken to an adjacent room from which the box was visible, and presented with the hose as well as 3 "distractor objects" - a rope, a bamboo stick and a sling. An hour after selecting one of these, the apes were taken in to the room containing the wooden box. During the first trial, all three apes chose the appropriate tool, despite encountering it only once before. In a total of 14 trials, one of the chimps chose the right tool 13 times; the other chimp and the orangutan chose it 14 times.

Then came the real test. Using the same apparatus and conditions as the second experiment, the apes were again presented with a selection of tools, but this time, the tools had with them the animals' favourite fruit. Thus the apes were faced with a choice: they could either take the fruit immediately, or they could select the hose, in anticipation of a larger quantity of food, which could be retrieved later on. To the experimenters' surprise, the hose was selected significantly more times than was the immediate reward, over the course of 14 further trials, suggesting that the apes were capable of favouring a future need over an immediate reward.

It is now believed that planning ahead - at least in humans - is dependent on episodic memory. Because episodic memory is reconstructive, anticipating a future event involves constructing a mental simulation based on fragments of memories of similar events that have been experienced in the past. This reresentation can then be used to predict the most likely outcome of a future event, and the best possible course of action. Evidence for this comes from studies which show that amnesics have difficulty picturing themselves in the future.

This study does not rule out the involvement of other forms of memory, but it does show that chimps and orangutans have planning skills that are, at the very least, similar to those of humans. The authors now aim to investigate planning in more distantly related species, and also in human infants, to try to determine when such skills develop.

Osvath, M. & Osvath, H. (2008). Chimpanzee (Pan troglodytes) and orangutan (Pongo abelii) forethought: self-control and pre-experience in the face of future tool use. Anim. Cogn. DOI: 10.1007/s10071-008-0157-0

Fraser, O. N., et al. (2008). Stress reduction through consolation in chimpanzees. Proc. Nat. Acad. Sci. DOI: 10.1073/pnas.0804141105.

Townsend, S. W. et al. (2008). Female Chimpanzees Use Copulation Calls Flexibly to Prevent Social Competition. PLoS One 3(6): e2431. DOI:10.1371/journal.pone.0002431