Lemurs – Can Field Work be Useful for Evolutionary Psychiatry?

As something of a hobby and in an effort to get a better grip on what evolution means, I have spent a relatively small amount of time filming primates. Indirectly my hope is that this will be helpful in better understanding the emerging discipline of evolutionary psychiatry. Evolutionary psychiatry is a theoretical branch within psychiatry that attempts to find theories of mental illness that are informed by the principles of selection (e.g natural selection). Given the complexities of mental illness it seems as though there is much to be gained from triangulating predictions from different models particularly as questions of discriminating genetic and environmental causes of different illnesses are inescapable. Along the way, the filming has been fun and getting to know a little of these creatures has been fun as well.

The human lineage diverged from that of Lemurs some 63 million years ago. Richard Dawkins coined the term concestor for the common ancestor that we share with another species (see review here). So using this terminology our common concestor existed some 63 million years ago. The Lemurs have a fascinating history more of which can be found here. Essentially Madagascar broke off from Africa and the evidence suggests that the Lemurs traversed the sea to get to Madagascar ‘catching’ a ride on floating vegetation – referred to as rafting events. The distance is estimated to have been a minimum of 350 miles (for a dog that was found at sea riding a sheet of ice over an estimated distance of 75 miles – see here). The end result of this is that on Madagascar, the Lemurs have been able to evolve relatively ‘peacefully’ with few natural predators. Elsewhere, the Lemur has not survived and it has been suggested that they have competed unsuccessfully with higher primates.

As an interesting aside, locals communities in Madagascar have built up different types of relationships with the various subspecies of Lemurs. Some are considered a bad omen and contact is thought to have an impact on the community. Others are protected by the local community and the Indri is also known as Babokoto (Ancestor of Man – although this translation is contentious).

So what is there to learn from the Lemurs. No doubt, those working in the field will have a very good knowledge of a number of fundamental characteristics of different species of Lemurs but there is the possibility of generating useful hypotheses when looking from a slightly different perspective. I’ve put together the most interesting footage in this video.

Now the game is afoot! Alas my powers of deduction are rather limited in comparison with the fictitious sleuth and so any suggestions from readers would be gratefully received.

There are three species of Lemur in the footage: The Black and White Ruffed Lemur, the Brown Lemur and the Ring-Tailed Lemur easily recognised from their names alone in this footage. My observations were thus

Aggressive Posturing: The Black-and-White Ruffed Lemur (BWRL) chased both the Brown and Ring-Tailed Lemurs which ran away fairly promptly. In two of the clips the chased Lemurs were eating. I’m not sure of the significance but the BWRL is rather large in comparison with the other two and size might play a role in dominance within the environment. Or the other two species might have been encroaching on the BWRL’s territory. However in one of the clips, the Brown Lemur is chased around over a large space making the territorial argument less likely. An alternative argument is that the BWRL is exerting it’s dominance in the environment with the goal of achieving a submissive response in the other two species. I didn’t notice the same response between BWRL’s (chasing) although there was a period of calling.  If the latter hypothesis is correct it suggests that the BWRL identifies the BL’s and RTL’s as targets for physically and vocally aggressive posturing perhaps on the basis of recognising them as different or from experience of prior outcomes in confrontations. There might be a combination of the two as I didn’t witness any initiation of confrontations with the BWRL from the BL or RT.

Hands: The BWRL’s hands are incredibly flexible. While watching them, the movement registered with me as very similar to the movements of a human hand. This is further reinforced by what the BWRL’s do with their hands. While setting up the camera tripod, I was (pleasantly) ambushed by a group of BWRL’s as can be seen at the beginning of the footage. At several points the BWRL’s can be seen to hold onto the tripod with both hands. Indeed one of the most remarkable points comes at between 6.00 and 6.20 (yes, slightly pedantic I know). The Lemur uses its hands to lift the tripod off the ground. What’s remarkable is that it doesn’t drop it but rather places it gently back in position. More on this later. There is also a point at 5.16-5.23 when the Lemur stares at it’s hands before licking them in turn. This period of staring was interesting and I wondered what it was thinking (it may have been responding to the smell of it’s hand).

Lifting up the tripod: The BWRL lifts up the tripod and replaces it. Then it pushes the tripod along the ground before ‘shouldering’ it. I got the impression that it was estimating the force required to push the tripod along the ground and was adjusting its movements accordingly. Superficially at least I got the impression that this was a fairly intelligent behaviour. It looked as though the BWRL was trying to understand the physical properties of the tripod. For want of a better term, it was trying to make predictions and I have argued elsewhere that this may be a biological correlate of scientific curiosity. Such curiosity in humans is usually attributed to the prefrontal cortex and to executive abilities.

Tapping: At 5.01 the BWRL taps the other BWRL on the shoulder head. I have seen such tapping described in RTL’s but no doubt this has been described in BWRL’s also. What is interesting about this is the differentiation from chasing the BL’s and RTL’s.

Group Behaviour: The BWRL’s act as a group. This is most noticeable when they examine the camera tripod. They act as a unit. My impression was that they demonstrated social cohesion. When they divided into two groups, the calling within the groups also suggested cohesion. There may be an element of competition – being the first to explore a novel object in the environment. The BWRL’s differentiated from each other in their persistence in examining the camera. Such differences might represent character traits or specialisation. The BWRL’s displayed periods when they chose to remain in each other’s proximity while noteably chasing away BL’s and RTL’s. Since the BWRL’s would be expected to differ in their strength in confrontations this may represent a species specific behaviour rather than one based on the predicted outcome in confrontations. This is further supported by the tapping behaviour.

Calling: Within the group there was a low pitch growl (LPG) and high pitched call (HPC). The HPC was repeated more rapidly than the LPG and was associated with small rapid movements (whereas the LPG’s seemed to be made whilst stationary). Following the shoulder head tap there was an accompanying third type of call of a more high pitched nature.  Perhaps this was to reassure the BWRL that had previously been using an LPG.  The LPG seemed to be a show of strength and the time taken to produce this may have resulted from the use of additional muscle groups compared to the HPC. The BWRL calling displays rhythmicity. Rythmicity is evident in human speech and music and musical rhythm has been identified in other primates. Perhaps some of the calling is an alternative to physical confrontation. The HPC’s also seem to be differentiated with a melodic component. It would be interesting to know if the individual vocalisations had independent meaning.

Winner Takes All. The BWRL’s were louder, more aggressive and more exploratory than the RTL and BL during my observations. In the natural habitat if this were to persist it might mean that they would have more opportunities to experience novelties and gain resources than the other two types. This would be transmitted not just through genetics but through culture also.

Conclusions

Our lineages diverged some 63 million years ago. The absence of significant predators on Madagascar may have resulted in subtler adaptations to the environment and we may be seeing species that are more closely related to our concestor than we are. Still there has been a lot of time for adaptation. Nonetheless assuming conservation of successful genes and valid similarities the following hypotheses can be generated

1. The flexibility of the hand may be an important part of human evolution possibly conserved over 63 million years and enabling a more rapid exploration of novel stimuli in the environment. A useful comparator here would be a dog or cat.

2. The flexibility of the hand may be related to exploration and to development of executive abilities. The representation of the hands in the motor homunculus in humans is evidence of their importance. The BWRL demonstrates evidence of a very flexible adaptation which expands the way in which it can interact with objects and other BWRL’s.

3. Social behaviour may have been an important aspect of human evolution and may have been evident 63 million years ago again if the genes were highly conserved. Acting as a group offers obvious advantages. The topic of altruism comes up in such discussions but in this footage it was pair bonding that may have produced social cohesion (e.g if the shoulder head tapping may have been a reassurance to end confrontatory calling).

4. The aggressive behaviour may over time lead one species to increase their territory and the number of challenges they are posed with consequent selective pressures. There may be a genetic tendency towards seeking out selective pressures (novelty seeking) that when paired with social bonding may move a species rapidly in a particular direction.

5. Rhythm and pitch may be an essential aspect of human speech that serves the dual purposes of confrontation and reassurance. At least from this footage and assuming that genes have been conserved over 60 million years.

If you have any suggestions please add them in the comments section. Many thanks to Rick Clarke who created the great music that was used in the video.

Index: An index of the site can be found here. The page contains links to all of the articles in the blog in chronological order. Twitter: You can follow ‘The Amazing World of Psychiatry’ Twitter by clicking on this link. Podcast: You can listen to this post on Odiogo by clicking on this link (there may be a small delay between publishing of the blog article and the availability of the podcast). It is available for a limited period. TAWOP Channel: You can follow the TAWOP Channel on YouTube by clicking on this link. Responses: If you have any comments, you can leave them below or alternatively e-mail justinmarley17@yahoo.co.uk. Disclaimer: The comments made here represent the opinions of the author and do not represent the profession or any body/organisation. The comments made here are not meant as a source of medical advice and those seeking medical advice are advised to consult with their own doctor. The author is not responsible for the contents of any external sites that are linked to in this blog.

3 thoughts on “Lemurs – Can Field Work be Useful for Evolutionary Psychiatry?

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