Unconventional Evolution: Notes from the “Cliff Jolly Conference”
As I mentioned just prior to my move to Sb, I spent this past Saturday at NYU at the “Evolutionary Anthropology at the Interface” conference, which was primarily a celebration of the work of Cliff Jolly. I’m still a bit over my head when it comes to knowing the full “Who’s Who” of evolutionary anthropology, but I do know that Cliff Jolly is most well known for his “seed-eaters” hypothesis of human origins, in which extant baboons (Papio sp.) are proposed to be better primates to study when considering primate origins and a seed-eating diet is put forward as one of the more important evolutionary changes that paved the way for later hominins. I won’t go into detail about the hypothesis here as I would like to stick to what was said at the conference at the moment, but hopefully I’ll be able to return to it for a more detailed explanation in the near future.
Even though arrived at the conference a little bit late, I did get to see the majority of Karen Strier’s presentation entitled “Seeing the forest through the seeds,” which focused on the Northern Muriqui (Brachyteles hypoxanthus) and its demography. As Strier pointed out, primates in dense jungles like those that the muriqui inhabit in Brazil can be difficult to research, and many studies on primates are carried out for a year or two. Larger overall trends are usually not recorded, however, as no one is there to see them. Fortunately, people have been studying at least one population of B. hypoxanthus for at least 25 years, and the size of the group has increased dramatically. Within a quarter of a century the population shot up from 22 to 83 (with 6 adult males initially and 25 now). Such a large increase in populations is certainly going to change how the behavior of the primates, and it seems that as the population size of the particular B. hypotxanthus group increased, a greater number of females dispersed outward and less immigrated in. How these changes will influence the population in the long-term, however, will require more study as these primates are relatively long-lived and the effects of a larger group size, female dispersal, and an increased number of adult males will require many years of research to understand.
Then came the topic of species conservation, and the general feeling of the conference was that species names are just subjective labels that are not anything to lose sleep over. What Strier related (and what some others echoed later in the day) is that if populations of an animal are deemed to be separate species for conservation reasons then establishment of a new species to represent a particular population (or smaller group of populations) is acceptable. I’m not altogether comfortable with such a notion, however, and even though the definition of a species can be a difficult thing to pin down (and that conservation of endangered species is very important) I think that taxonomy should reflect evolutionary relationships and not be made more artificial than necessary by creating new species when such reshuffling of taxa doesn’t seem to have scientific support. I am not especially experienced with the intersection of science and conservation policy (at least, not yet), but I was a bit unsettled by the prospect of primarily creating “new” species when such divisions may not accurately reflect what exists in nature.
Alan Walker was up next and spoke about strength in great apes and humans, indulging in a bit of (as he called it) “fantasy”. He mentioned some interesting research involving the spinal cords of Chimpanzees (Pan troglodytes) and humans, and noted that while the spinal cord of chimps is short there is more grey matter in the cord associated with the arms and legs, showing a trend towards more powerful limbs but sacrificing finer motor controls. Walker then associated such trends with the length of forearms in apes, noting that the longer the forearm of an ape the more powerful the swing of the arm may be, but control (as in throwing) would be lost. The “fantasy” aspect kicked in here, Walker suggesting that the larger brains of the Homo lineage evolved as a result of having a longer spinal cord and more motor control (the implication being that throwing objects might have had something to do with it). An interesting hypothesis, but at present there seems to be correlation without much proof of definite causation.
Ken Weiss was up next, and it was a little difficult to follow this one. I have to admit that I have a stronger background in paleo, anatomy, and zoology than I do in genetics or evo devo, but I think I was able to take in the main points of the presentation. Weiss kicked things off by talking about hyrbidization between Olive Baboons (Papio anubis) and Yellow Baboons (Papio cynocephalus), using the potential hybridization between two “good” species to suggest that variations which may seem to be indicative of species might not reflect actual reproductive barriers (although there seemed to be some uncertainty as to whether the baboon hybrids were sterile or not). The most interesting (and contestable) aspects of the lecture came towards the end however, Weiss proposing that evolution was generally tolerant of species-level variations and that speciation could be “non-adaptive.” This definitely caught my attention, and what Weiss seems to have meant was that there could be some chromosomal change that could reproductively isolate a population, causing speciation without major phenotypic change or adaptations to a differing ecology. Such an idea is definitely interesting, but it seemed to be proposed as a hypothetical and no examples were given of such a phenomenon being observed. Weiss definitely was a bit guarded at this point, stating that he wasn’t “a cladist” and he didn’t have his body armor on, but the overall proposal seemed to be that genetic changes drive evolution and speciation at a very gradual rate, natural selection playing a more diminished role in the “origin of species.” Being that I attended the conference with a group of paleoanthropologists, we grumbled a bit about this on the way to lunch, but what Weiss suggested is intriguing even if it seems to be lacking observational evidence at the moment.
After lunch Linda Vigilant spoke about using DNA studies in terms of population studies, and research on the Cross River Gorilla (Gorilla gorilla diehli) provided the primary example. The studies Vigilant mentioned seemed to show that there appeared to be some amount of migration between reproductive groups of the elusive gorillas (the studies were conducted based on fecal samples, DNA studies allowing researchers to potentially identify which groups are mating with which other groups due to dispersals and immigration.
Then came the “main event,” a lecture by Cliff Jolly himself. I suppose I would have gotten more out of it if I was more familiar with his work going in as the lecture seemed to be short on observational evidence. I’m not suggesting that such evidence doesn’t necessarily exist (I’ve been able to find some papers on baboon hybridization that I have to take some time to read this week), only that it was not mentioned in the lecture and this made some of the ideas a little hard to swallow. Jolly started off strong, though, reminding the audience of the role of contingency in evolution and that the evolution of Homo sapiens was not destined to be. In fact, Jolly provided a wise warning to those concerned with human origins; the focus of extinct hominin studies should be on how they actually lived, not on how “human” they were in whatever respect. Hence, he proposed that baboons were better models for human origins as they were further removed from us than chimpanzees or bonobos, but this hinges upon the supposition that extant baboons occupy a similar niche as some extinct hominins and have a similar natural history as well. This (pardon the pun) seems to stem from the seed-eating hypothesis, baboons being the prime examples in the idea, and although using African apes as models for human origins can lead to some amount of bias I don’t think they should be disregarded because they are “too close” to Homo sapiens for researchers to be objective; the closest living relative of any taxa provides important clues about evolution, and while care might be needed in making inferences or carrying out research they can often best help illustrate contingency and convergence.
Much of what Jolly mentioned, however, had to do with the idea of “mitochondrial capture,” or mitochondrial DNA indicative of one species being present in another. The proposed method for this had to do with dispersal, large populations kicking out males that ended up breeding (and hybridizing) with another closely related species, eventually leading to animals with the phenotype of one species but the mitochondrial DNA of another. Olive and Yellow baboons were the primary examples here, but little actual data was mentioned to back up the hypothesis. In fact, I had never heard of the concept before and I will have to look into the subject more closely as I would definitely like to know what evidence such ideas were based upon.
So that’s the basic version of what I took in this past weekend, and the conference definitely provided much food for thought. Are Yellow and Olive baboons hybridizing? Are their offspring sterile? If they are hybridizing, could other populations be producing hybrids as well? Why would Yellow baboons mate with Olive baboons? Are the male Olive baboons just mating with the Yellow Baboons or are they staying in the group? Perhaps some of the literature I’ve been able to find will help shed light on some of these questions, and I’ll write about it more fully when I’ve given myself a better background on the subject.