Darwin day

ASU expert selects Darwin Day answers, naturally


Deanna Dent

It’s easy to watch the evening news and assume Homo sapiens is one of the most recalcitrant species on the planet. But humans are, surprisingly enough, one of the most cooperative species, and we evolved to be that way, according to one Arizona State University expert.   

Institute of Human Origins Director William Kimbel took time to share a few answers with ASU Now on the study of evolution, just in time for Charles Darwin Day on Feb. 12. 

Question: What do we get wrong about the term "natural selection"?

Answer: A lot of people have the idea that natural selection is a circular argument. If natural selection is the survival of the fittest, then the fittest survive and so the cause and the effect are related to one another. 

Darwin’s description of natural selection was not based on survival of the fittest; it was based on the idea that individuals who inherit characteristics that enable them to survive and reproduce in particular environments — where those traits are at an advantage — that these characteristics will increase in proportion to the traits that are less well-suited to solving these environmental problems, so it’s really about differential reproductive success.

Q: How has the study of evolution evolved since Charles Darwin? 

A: We know about the mechanism of inheritance, DNA and how it underpins the transmission of heritable characteristics from one generation to the next. That mechanism was unknown to Darwin and his contemporaries, and while they had an incorrect understanding of inheritance, it didn’t affect Darwin’s ability to put forward a valid theory. The mechanisms of inheritance were obvious for everyone to see through breeding, experiments and so forth.

But our record of human origins is vastly increased in quality and density over time compared to what Darwin knew, and so we inherit Darwin’s mantle as the guiding theoretical framework as our understanding of human origins.

We now have a rich database to consult on the details of that evolution and the causal prophecies: the why and the how and so forth that are responsible for how humans became such a dominant species on the planet.

Q: What did Darwin get wrong? 

A: He didn’t understand inheritance because he didn’t have access to a rich fossil [human] record. In "The Descent of Man," published in 1871, he describes an explanatory model for how humans became differentiated from the tree-dwelling apes.

He put down a model which became hugely influential in the field of human origins. It posited that human ancestors came down form the trees to the ground and adopted an upright posture on the ground, hands were freed from locomotor constraints and became able to be used instead for the manipulation of the environment principally through tool-making and that tool-making had a stimulating effect on intelligence as read through brain size. Tools also replaced the giant dagger, like canine teeth, which had commonly been thought to be used in defense.

He wrote it as though all the components of that model would have evolved more or less simultaneously.

What the fossil record tells us is that a lot of the pieces of that model don’t appear in the geological record at the same time, which means they can’t possibly be explained all at once with one encompassing model that endows our first ancestors … with all of those characteristics. 

So Darwin got far more right than he got wrong, and much of what he got wrong was simply because the answers that we now have were not available to him. 

Q: What should we be excited about in the field of paleoanthropology? 

A: All of it. I’m not being cute. 

There are numerous questions being pursued now from a variety of evolutionary perspectives on questions about how we became human. What were the causes of the divergence of our line from the line of the ancestor we share with the chimpanzee line? We know approximately when that happened, thanks to the molecular clock, based on the DNA differences.

And then there is the relationship between stone tools. The oldest stone tools have typically been associated with the rise of our own genus Homo about 2 million to 2.5 million years ago, but now we have very crude stone tools associated with fossils around 3.3 million to 3.4 million years ago.

There are new fossils being found in Africa that bear on the earliest stages of the rise of our own species. We now have the addition of genetic, DNA evidence into that story. 

One of our own scientists, Curtis Marean, works in South Africa on the Cape Coast, (which) has some of the earliest evidence, archeological evidence, for modern humans. We want to try to understand how modern human behavioral characteristics created advantages for populations that enabled them to spread across the continent and ultimately out of Africa and to populate the rest of the world as we’ve done. 

Q: Is Homo sapiens still evolving?

A: So the answer is yes, but it’s different. If you went back to Lucy’s time or the earliest Homo sapiens or any of the number of species in between, our evolution would look rather different. At some point in the past we started to evolve predominantly in terms of our culture rather than our physical features.

Make no mistake, our genetic evolution is still occurring. Much of our evolution, especially the fastest part of it, comes from our unusual ability to transmit information through technology from generation to generation. Our ability to transmit cultural information and to cooperate on a massive scale, those are fairly recent events in our evolution that can be taken from the most recent prehistoric periods right into the historic periods of our history. 

We have scientists here too as part of the Institute of Human Origins group who are investigating this with folks who are interested in the origins and the evolutionary advantages of large-scale cooperation in different types of societies today. They are comparing it to the work that the folks are doing on the great apes, looking for how or if they cooperate. From a large-scale perspective, a lot of the action late in our evolution has to do with the evolution of our culture and how we became the most cooperative species on the planet.


Top images courtesy of New York Public Library digital collections