During the long wind-up to this autumn’s congressional elections, hardly a week went by without a gaffe by Delaware tea partier and Sarah Palin-wannabe Christine O’Donnell. The sharp-tongued political commentator Bill Maher seemed to have an entire stockpile of embarrassing clips from when O’Donnell – then president of the conservative advocacy group the Savior’s Alliance for Lifting the Truth – regularly appeared as a panelist on his show Politically Incorrect during the late 1990’s. Among the political blooper reels was this little gem, in which O’Donnell makes clear her opinion of evolution (no prizes for guessing what she thinks of it):
That’s a minor twist on the old creationist chestnut “If we evolved from monkeys, then why are there still monkeys?” It’s one of those questions which is so wrong at its root that it requires the responder to explain why the entire premise is baloney in addition to providing positive evidence of why we should fully expect for monkeys to still exist, and it is based from a common misconception of evolution that is sometimes shared even among those who regard evolution as true.
The traditional imagery of evolution is of a linear march of primitive ancestors leading up to an advanced descendant. Slimmed down versions of the outdated, hierarchical Great Chain of Being, these illustrations imply that evolution has an inherent upward trend which drives life along a ladder of increasing improvement. Collateral relatives are trimmed off to highlight change along a linear pathway, and can we really be surprised that some people take this imagery to indicate that descendant forms must replace their archaic predecessors? When we present evolutionary change along these strictly linear pathways, we are shooting ourselves in the foot by perpetuating an inaccurate form of “missing link” imagery which we know falls far short of the wildly branching pattern evolution actually creates.
National Center for Science Education staffers William Eric Meikle and Eugenie Scott have just published a new paper considering this problem in the latest issue of Evolution: Education and Outreach. The “Why are there still monkeys?” question just refuses to go away, and indicates a major misconception about evolution that educators must be prepared to face. As a remedy, Meikle and Scott suggest using the concept of cousins.
In any family tree you care to draw – whether from a broad evolutionary perspective or a narrowed genealogy of close relatives – each point among the branches is going to fall into one of two categories: linear relatives and collateral relatives. Your parents, grandparents, great grandparents, etc. are all linear relatives, while cousins, uncles, and aunts are collateral relatives who are more closely related to you than most other people but are not direct ancestors or descendants. That’s simple enough, and the same sort of logic can be applied to evolutionary relationships.
During part of the evolutionary history of our species, our ancestors were monkeys. (Just as our ancestors were cynodonts, tetrapodomorphs, gnathostomes, etc. etc. etc. at different points in time.) If we had a complete roll of all the animals which ever existed during prehistory and a few years to do the work, we could trace our direct line of ancestry through a succession of anthropoid primates nested within a tangled tree of diverse species, some related to modern monkeys and others not. We share a common ancestry with all living monkeys, but extant primate species are our evolutionary cousins and cannot be cast as representing our actual ancestors. It may be simple, but this idea of branching is essential to understanding how evolution works.
The English anatomist Thomas Henry Huxley recognized the value of using proximal, family-level relationships in elucidating evolutionary relationships nearly a century ago. In 1870, during a lecture about transitional forms in the fossil record, Huxley pointed out that we must take care to distinguish between”intercalary types” – evolutionary uncles and nephews – and “linear types” which could be cast as fathers and sons. The evolution of horses from Anchitherium through Hipparion to Equus was a sequence of linear types, Huxley stated, while the transition from small dinosaurs such as Compsognathus to flightless birds to flying birds was a series of intercalary types which only represented the forms of the as-yet-undiscovered animals in the linear sequence. Huxley would turn out to be wrong about the details of both sequences, but the point is that he recognized the need for naturalists to separate true ancestor/descendant pairings from collateral relatives which might inform us about what happened during a transition without actually being a part of it.
But I think we need to go a step further than pointing out that we did not evolve from living monkeys. After all, viewed from an evolutionary perspective, we are apes, monkeys, primates, euarchontoglires, eutherians, and so on. We surely can look at the diversity of living species and ascertain our degree of relatedness to them, but for those relationships to truly make sense we need to widen the picture to incorporate the context of the fossil record. When placed against the background of deep time, the branching pattern of evolution and the fact that splitting is the rule rather than the exception is much more starkly apparent than if we use living species alone. Granted, we are typically dealing with Huxley’s intercalary types in this circumstance, but even if we lack confirmed ancestor/descendant pairs we can still nest our species within various diverse groups of primates and more powerfully present the fact that our species is just one type of peculiar primate which has been evolving alongside other primate species. When you get right down to it, it’s all a matter of perspective.
Meikle, W., & Scott, E. (2010). Why Are There Still Monkeys? Evolution: Education and Outreach, 3 (4), 573-575 DOI: 10.1007/s12052-010-0293-2
Zalmout, I., Sanders, W., MacLatchy, L., Gunnell, G., Al-Mufarreh, Y., Ali, M., Nasser, A., Al-Masari, A., Al-Sobhi, S., Nadhra, A., Matari, A., Wilson, J., & Gingerich, P. (2010). New Oligocene primate from Saudi Arabia and the divergence of apes and Old World monkeys Nature, 466 (7304), 360-364 DOI: 10.1038/nature09094