The Full Spectrum

Let’s talk for a moment about the special status that humans have in the natural world — or rather, the special status that we often accord ourselves.   Though most people no longer think of the world in terms of Aristotle’s scala naturae, we still have a tendency to consider ourselves unique, separate from and far more advanced than the rest of the animal kingdom.  And it’s true that humans do lots of things that other animals don’t: we  build cities, we fly airplanes, we write books (and blogs) and create works of representational art.  As a species, our accomplishments are substantial.

But if there’s one thing that modern ethological research has demonstrated, it’s that many of our abilities and behaviors can be found at least to some extent in other species, especially in the primate family.  Since Jane Goodall’s early observations of tool use among wild chimpanzees at Gombe Stream National Park led her academic adviser, paleoanthropologist Louis Leakey, to comment that “now we must redefine tool, redefine man, or accept chimpanzees as human,” several once-vaunted hallmarks of humanity have been eliminated from the list of defining characteristics that separate Homo sapiens from other species.  Primatologists have provided evidence that chimps hunt, participate in campaigns of organized aggression toward neighbors, maneuver for status in Machiavellian ways, and reconcile following conflict.  Research on language use by great apes similarly suggests that in many cases the difference between humans and our closest relatives is one of degree rather than kind.

The existence of this behavioral spectrum  has been illustrated yet again in the new issue of the journal Current Biology, in which anthropologists Richard Wrangham and Sonya Kahlenberg report that young chimpanzees in Kibale National Park in Uganda carry and play with sticks in a manner similar to children with dolls.


A female chimpanzee holds a “stick doll” between her leg and body. (Sonya Kahlenberg)

Examples of play among juvenile animals are not new.  But it is intriguing that these researchers identified a sex-based bias in their data: as in humans, female chimpanzees were more likely to carry stick dolls.  Does this mean that young females are simply practicing for the future by imitating the mothering behaviors they observe within a group?  Or might it suggest innate psychological differences between young male and female chimpanzees?  In either case, how do these data pertain to studies of sex/gender differences in humans? Nature/Nurture debaters, start your engines!!

Whatever the long-term implications of this new study, it serves to illustrate that the more we learn about the behavior of other animals, especially apes, the less reason we have to consider ourselves wholly separate from them.  Of course, this isn’t to say that you should expect to see orangutans in Indonesia building treehouse cities anytime soon.  But try not to be too taken aback the next time you read a story about a wild animal doing something “surprisingly” human-like.
To read more about play-related sex differences in non-human primates, click here.  And don’t forget to subscribe to The Tinkering Primate if you want to get emails about new posts.  Just click the “Yes Please” button underneath the chimpanzee on the site banner.


The Basics

If I had to choose three adjectives to describe Darwin’s theory of evolution by natural selection, they would be:

1. Elegant
2. Powerful
3. Simple

Yes, simple.  Although evolutionary biologists now know that forces other than natural selection (e.g. genetic drift and gene flow) can cause populations to evolve, Darwin’s theory still provides the basic framework for understanding the history of life, and explains much of the variation we see on our planet.  And it does it with just three premises (hence my simplicity claim).  Any student who passes through my Introductory Biological Anthropology course can recite them for you:

1. Individuals in a population vary
2. Variation is heritable
3. Because of this variation, certain individuals are able to survive and reproduce more successfully in a given environment than others.

That’s it.  Those three premises are all that is required to understand the idea of evolution by natural selection.  So why is there so much confusion and misunderstanding surrounding Darwin’s ideas?  Why, during last year’s celebration of the 200th anniversary of Darwin’s birth and the 150th anniversary of the publication of On the Origin of Species, did a poll reveal that only 4 out of 10 Americans believe in evolution?

The ongoing evolution vs. creationism/intelligent design battle aptly demonstrates that religious background plays a significant role.  But in some cases, people may not believe in evolution by natural selection because they don’t understand the process.  Many misconceptions abound simply because people haven’t been properly introduced to the Darwinian basics.

So in the spirit of defending evolutionary thought, I want to share a few  clarifications that I have found useful when introducing students to Darwin’s theory of evolution by natural selection.

  • The third premise — that because traits vary, certain individuals are able to survive and reproduce more successfully in a given environment than others — is often abbreviated to “Survival of the Fittest.”  But this shorthand only works if people understand that the term “fit” is relative.  Individuals that are highly fit (i.e. able to produce many offspring) under one set of environmental circumstances are not necessarily the “fittest” under different conditions.  In other words, changes in an organism’s habitat can turn underdogs into winners and vice versa.  This is key.  Remember it.
  • Natural selection and Evolution are not terms that can be interchanged at will.  As I tell my students, natural selection is a process that affects individuals, but it is populations that evolve as fitter individuals reproduce more successfully and pass on beneficial trait variations.
    A quick example: Among a population of tree frogs, bright red individuals who are more visible against the green backdrop may be subject to higher predation and die before they reproduce.  As a result, fewer “red color” genes will be passed on to subsequent generations and over time the population will have higher frequencies of the beneficial-for-camouflage “green color” genes.
  • Humans (aka Homo sapiens) are not the pinnacle of evolution.  In fact, there is no pinnacle of evolution, because natural selection is not a unidirectional process in which organisms become “better” in an absolute sense (see the above point about underdogs).  Humans are simply the most recently evolved members of one particular primate lineage.  And, despite what many of my students think, most experts agree that we are still evolving.

That’s the end of today’s lesson.  Now go and explain these premises to everyone you know and maybe, just maybe, we can top 50% in the next Gallup poll.

A fool’s experiment

I recently stumbled across the following quotation from Charles Darwin:

I love fools’ experiments.  I am always making them.  [From The Life and Letters of Charles Darwin, 1887]

This got me to thinking.  Like many of my colleagues, my voyage through graduate school has been a tumultuous one.  But never in these lo-so-many years have I lost interest in learning, reading, and talking about nature and science.  Moreover, the teaching experience I have acquired has given me the itch to educate others.  My friends and husband are frequently subjected to  enthusiastic ramblings about recently-read facts, newly-published theories, and anthropological oddities.  For example, did you know that the average chimpanzee sexual encounter lasts only 7 seconds?  My friends do.

But I’ve decided I can bend their ears only so far.  I need a broader audience.

And thus begins my fool’s experiment.  With this blog, I hope to act as a modern-day naturalist, sharing the progress I make with my own research, thinking and writing about scientific topics, and reflecting on the academic world.  I hope that you will visit often to join me in the endeavor.