The human species – a naturalist conjecture

One question still unanswered in biology and one that is of special interest to me is what happened to our evolutionary branch that made us so different than our nearest relatives on the evolutionary tree, the chimpanzees and bonobos? Putting aside supernatural explanations as well as wild speculation about aliens doing genetic experiments on our race as something to do while taking a break from construction of the pyramids, the correct explanation will be provided by science.

An excellent article on the Smithsonian’s webpage states that the difference between our DNA and our nearest relatives on the evolutionary tree is about 1.5%. It is within this difference that the mutations that make us uniquely human are most likely to found. There are various conjectures at this point but the one that rings the most true to me comes from a talk given by Dr. Brian Thomas Swimme which I was fortunate to stumble across a few years ago. The narrative goes something like this:

When you compare human infants and chimpanzee infants the similarities are striking. As they develop, like most mammals, the young enter a period of play and exploration necessitating a constant eye on them by the mother and the extended family. This period of play by young mammals is observable in all other species of mammals such as dogs, cats, bears lions, and even Orcas. In most mammals this period is short lived compared to humans, even in species that have comparative lifespans to ours. Soon after this phase in most other mammals the genetic programs kick in and the adult forms emerge complete with the physique and skills necessary to be lion, or a chimp or any other adult mammal. Not so with the human. It appears that the genetic programs that are activated in our closest and most distant cousins are not activated in humans. We retain a lot of the physical and mental features we had in childhood and adolescence. How might this be explained and what are the implications for us as humans?

There is a set of genes called the Hox genes which control the rate of development in animals. The conjecture is that there was a mutation or a series of mutations in the Hox genes in humans which resulted in the slowing down of our development. While most species’ young stay in that playful and explorative phase for a brief time, humans in many ways never develop out of it. We retain that wonder and drive to explore our surroundings throughout our entire lives. In other words, compared to other mammals, members of our species never completely ‘grow up’ and the genetic programs that kick in to make a Chimpanzee a Chimpanzee never kick in for the human. As Swimme speculates, there are profound meanings for us if this is the case. We retain that wonder and, as we mature, it changes into a desire to know and understand. We retain that playfulness and our desire to play and enjoy ourselves still fills us with longing. There are also other implications to this. When the genetic programs kick in to transform a tiger cub into an adult tiger all the necessary knowledge and skills are included. No one has to teach a tiger how to be a tiger; the DNA does that. In humans, this is not so. The adult genetic programs, specifically the ones telling us ‘how to adult’ never get turned on. What does this mean? In a very real sense it means that humans don’t know what they should do. Lions and tigers and bears don’t suffer from the search for meaning and purpose, a search that seems to have afflicted humans throughout our history.

It is an interesting conjecture that, on the face of it, seems to point in the direction to where our uniqueness as a species can be found. I’m hopeful that I will still be alive when the conjecture becomes theory.

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Comment by Tom Sarbeck on February 14, 2018 at 3:57am

Richard, there's another candidate for the cause of humans' differing from bonobos and chimps.

Recently while doing some incidental reading, and not taking notes for academic writing, I saw words about structures in the human throat area that don't exist in the bonobo or chimp throat areas. Those structures make speech possible.

Support for Swimme's hypothesis would require longitudinal studies of many individuals. Are there any such studies? 

Comment by Frankie Dapper on February 13, 2018 at 4:18am

I dont buy it. One by one the chimera of human uniqueness has fallen in the light of evidence. We humans of the west including scientists have had a religiously and or anthropomorphically preconceived idea of how we are special creation. 

Does not seem to me that primates stop playing all of a sudden at the onset of adulthood.  Same for domestic dogs. 

If the search for meaning is unique to humans then why do elephants travel great distances to visit their dead? Why do chimps have rituals that are speculated by some to be nascent religion?

If predators have a preset code in their dna to be adults then why do so many predators raised in captivity fail in the wild? Is it for the obvious reason that they need to be taught?



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