For decades, Americans have been told that we are an exceptional people with the unapologetic connotation that we are really better than the rest of the world’s mortals. Recent headlines have made it clear that we are indeed exceptional but not in the way that you might think. We are worse than other societies in the industrial world when it comes to healthcare, education, wealth disparity, and more.
But, enough with the politics already. What I really want to focus on is whether all human beings, not just Americans, are better than other types of animals. Or, if not better, aren’t we, at least, significantly different?
This question has occupied thinking humans (Homo sapiens) since the early days of written history. Indeed, even King Solomon, the wisest man of his times (10th century BCE), was said to have pondered the question: “What makes the human superior to field animals?” Indeed, he counseled others to observe the ways of the ant—and be the wiser for it.
Since those ancient days, variations of this question have occupied some of the best minds of the human race, from Plato in the 5th century BCE to the molecular biologists, neurobiologists, neuropsychologists, and philosophers of the 21st century.
What sets up apart?
For a long while, it was thought that intelligence set us apart from the “lower” animals, but we now know better. Whales, dolphins, crows, parrots, and apes, to name a few, have also been shown to possess a high level of intelligence.
Is it our self-awareness that makes us unique? Not quite. Apes have been found to demonstrates varying degrees of self-awareness.
Perhaps, it is our communication skills? They are indeed highly developed, but they are not unique; whales, dolphins, birds, and apes all communicate via quite complex languages.
It has been suggested that our capacity to feel and show empathy is uniquely human. But, have you ever seen a video of a mother elephant grieving over her dead infant? And watched as the whole herd commiserated with her? Have you heard of the African buffaloes who form a protective shield around a female who is giving birth, to ward off predators and vultures?
In short, we are becoming increasingly aware that all these “human” traits started evolving millions of years before the first human descended from the trees to take his first tentative steps in the African savannah. We are only incrementally more evolved than the other animals. But, wait a moment, there’s another consideration.
We plan for the future
Daniel Gilbert points out in his bestseller “Stumbling on Happiness” that
“The human being is the only animal that thinks about the future.”
And he adds a significant caveat, “…the long-term future.”
My dog does plan for the near future (minutes from now) and stations himself by his food bowl about 9 AM when his breakfast time rolls around. But is he planning to send his offspring to dog school? Does the silverback gorilla in the impenetrable forest of Uganda worry about the potential effect of global warming on the food supply for his troupe 5 years from now? Not that we know and experimental evidence suggests that they don’t. Whatever looks like a long-term pre-planned activity, like birds building a nest for the future chicks, is believed to be the result of genetically pre-determined, automatic behavior.
If we accept the notion that we are only animals that plan for the future, then it begs the question: What is the underlying genetic and neuronal basis for such a breathtaking jump from an animal living in the present to one that is worried about the future and is planning for it? As an extension of that, let me add the observation that we are the only species that, as part of our awareness of the future, wonders about our role in the world, and is concerned (frightened?) about dying one day.
The progress of evolution
Kelley Harris studied mathematics as an undergraduate at Harvard and transitioned into genomics during a postgraduate year at the Wellcome Trust Sanger Institute in Cambridge, UK. She then earned a Ph.D in mathematics at U.C. Berkeley with a designated emphasis in computational biology. Her work received the Science & SciLifeLab Prize for young scientists. Without getting into the mathematical/genomic weeds, let me focus on the conclusion of her work.
The popular “molecular clock” model of natural selection posits that mutation rates evolve very slowly over, perhaps, tens of millions of years. This is the basis of the gradual quantitative accretion of mutations during evolutionary time. For example, our biological clock and that of the lowly yeast are very similar. Yeast emerged about 1.5 billion years ago, archaic Homo evolved about 600,000 years ago, and modern H. sapiens about 300,000 years ago. Over a billion years and hardly any significant genetic change. But Harris’s work demonstrates that DNA replication fidelity is a lot like other biological traits, sometimes evolving at a snail’s pace and sometimes evolving by leaps and bounds for reasons that usually eludes us.
Circling back to us vs. other animals
One would speculate then that if there is a qualitative difference between us and our closest relatives, the gorillas, chimps, and bonobos, it must have been one of those “leaps and bounds” that Harris’s work demonstrated. But why speculate? An international team of 38 scientists led by Nenad Sestan of Yale University just published a magnificent accomplishment in the quest for what makes the human brain unique.
The investigators focused on 16 regions of the brains of adult humans, chimpanzees (ape), and macaques (monkey) involved in higher-order cognition and behavior. They looked at the genetic information in the cells of these regions by sequencing the total mRNA of each cell. mRNA is the molecule that transcribes a gene from the DNA code into a protein. The total population of a cell’s mRNA is known as its transcriptome.
They went further. They overlaid the data of each cell’s transcriptome on histological sections of these tissues, and could thus get an integrated picture of every cell in a tissue and its genetic and protein content.
In addition to all kinds of variations in the molecular and cellular features between human and chimpanzee, there was one finding that takes your breath away. They found some rare cells that are present in humans and are completely absent in chimpanzees and macaques.
These cells are located in the striatum, a nucleus (an agglomeration) of neurons in the midbrain. The name, striatum, comes from its appearance as stripes of gray and white matter. Some cells in the striatum are activated by the neurotransmitter glutamine. Other cells are activated by dopamine. Functionally, the dopaminergic (dopamine-responsive) striatum cells coordinate multiple aspects of cognition, including motor- and action-planning, decision-making, motivation, reinforcement (which carried to an extreme can end up in addiction), and reward perception.
To close the loop
The newly discovered human-specific cells (called dopamine interneurons) were found to secrete dopamine! Is this the location in the brain that makes us exceptionally, well…human?
Still some important unanswered questions:
- Which cells in the striatum do those dopamine interneurons communicate with?
- What functions do these cells perform?
But Daniel Gilbert’s observation that
“The human being is the only animal that thinks about the future”
may be getting a solid cellular and molecular basis. And, that my friends, is pretty exciting.