Peter, a 100+ pound German Shepherd, shares our home. King of the urban jungle, right? Wrong, more love-bucket than fierce fighter. Still, Peter would probably take a dim view of an intruder, especially teamed up with his mate, Haley, another German Shepherd. Normally, Peter sleeps at night on his bed on the floor next to my place in bed. Unless, that is, it storms, the wind blows, it rains, or the house creaks. Then this mighty canid hops on the bed, curls up comfortably next to a convenient human, and seeks protection from whatever evil lurks.
Some courageous, or perhaps just inordinately hungry, ancestor of Peter crossed the line of light thrown by prehistoric campfires from outside in the shadows and cold to inside its light and warmth perhaps 15,000 years ago and began the transition from wolf to the current lineage of domestic dogs. Earlier versions of dogs may appear in archaeological deposits slightly over twice that age. DNA sequencing indicates that the molecular distance between wolves and dogs may be 100,000 years, and that German Shepherds may be a little closer genetically to wolves than other dog lines. Whether the earliest domesticated dogs date from around 33,000 years ago based upon the earliest archaeological evidence, or were more widely domesticated by 15,000 years ago, dogs and humans have linked their fortunes for thousands of years.
Dogs are mammals, and, like the primate lineages that include humans, both Carnivora and Primates experienced success during the adaptive radiation of mammals. A study in the journal Science in February 2013 reports that scientists compared 4541anatomical and genetic characters from 86 living and extinct species to posit that the last common ancestor of all placental mammals lived shortly after the end of the Cretaceous Period about 65 million years ago. Within two to three million years later, many of the current mammalian orders were established. Although mammals predated the end of the Cretaceous, and some studies based on molecular data indicate an earlier common ancestor, in either case it seems that the extinction of dinosaurs at the end of the Cretaceous was a necessary precondition for the adaptive radiation of the mammals.
The earliest primate, the order to which the modern prosimians, monkeys, apes and humans belong, may be the fossil Purgatorius, little mouse-like guy who lived about 65 million years ago, with the primate lineage established by about 55-58 million years ago. The earliest members of the Order Carnivora appear about the same time, which includes the canids, or dogs and their ancestors. The first clearly identifiable member of the dog family appeared about 40 million years ago.
Peter the German Shepherd and I probably shared a common ncestor shortly after the extinction of the dinosaurs. That sounds like, and is, a considerable period of time. But we get a different perspective when we consider our common lineage before our two lines split.
Put another way, from the dawn of simple single celled life on earth 3.6 billion years ago, until Peter’s and my last common ancestor about 65 million years ago, we shared a common ancestral lineage for 3,535,000,000 years, or 98% of the time until now. From the time of the earliest vertebrates, Peter and I shared a common lineage for 460,000,000 years, or 88% of the time. Differentiation between species and degree of separation depends a good deal upon your reference points. If your reference point is first life on Earth, dogs and humans look like brothers and sisters; if your perspective is from the earliest vertebrates, we still look like first cousins.
Traditions in the history of thought often hundreds or thousands of years old emphasize the uniqueness of humans and the distinctiveness of Homo sapiens from all other life. This rather unbalanced view arises from a number of reasons. One is simply because we are the ones originating the comparisons. The history of the world is full of examples of one group of people thinking it is superior to the others next door. Every society on Earth has explanatory stories about how people and other life forms came to be. Originators of these stories did the best they could to explain the world around them. The notion of the supremacy of humans over all other forms of life is another example, certainly characteristic of western thought. These traditions, mostly pre-scientific, have come down to us before we had firm knowledge of deep time and understanding of the origins and complexity of life.
Archbishop Ussher (AD 1581-1656) famously calculated hat God created the Earth on a Sunday in October 4004 BC. To be fair, he was using information most familiar to him, and in AD 1650, 4004 BC sounded like a long time ago. Sometimes one still hears literalists claim the Earth is 6,000 years old. Not until about the 1830s had our geological knowledge advanced sufficiently that scientists suspected that the Earth might be many magnitudes older, and only in the last half century radiometric dating has allowed us to calculate the ages of the Earth with considerable accuracy. Similarly, Darwin published On the Origin of Species in 1859 and established the idea of evolution of life through processes of natural selection. After Darwin, biology moved from a descriptive to an explanatory science. There is no going back now: science has established deep time and the evolution of life as firmly as our certainty that the Earth orbits the Sun. These scientific realities exist in parallel to the earlier explanatory models based on pre-scientific precepts.
The zoologist and paleontologist Stephen Jay Gould made the argument that we might consider bacteria the most successful of Earth’s life forms. Bacteria are among the simplest and earliest organisms. They exist in multiple habitats. Trillions occupy the human gut, making our lives possible.
They exist in earth and water, about as deep as we can drill underground, in exceedingly hot (600+ F) deep sea vent fissures, in a lake a half-mile underground in Antarctica, and in many other contexts. The total biomass of bacteria may exceed that of all plants and animals on Earth. People love to claim that humans are the most successful organisms in the world. Before we crow too loudly, we should wait to see how we fare against bacteria over time.
Dinosaurs arose about 230 million years ago from a group of archosaurs, the dominant tetrapod land vertebrates in the early Triassic. There are two great clades of dinosaurs, saurischian (lizard-hipped) and orinithischian (bird-hipped). The latter includes animals like stegosaurus and triceratops. The former includes sauropods, the massive plant eating beasts with long necks and small heads of the Jurassic; the theropods, the great bipedal carnivores of the Cretaceous, including the tyrannosaurids; and birds. Birds are the only exception to the extinction of the dinosaurs at the end of the Cretaceous, 65 million years ago. That little birdie on the telephone line had a common ancestor with the great theropod dinosaurs of the Cretaceous, like Tyrannosaurus rex.
These mighty creatures ruled the Earth for over 150 million years, yet often popular opinion considers them evolutionary failures. If we stretch the definition a little, humans arose about three million years ago. Is anyone betting that the human family will be around another 147 million years, to make us as successful as dinosaurs?
We might think of our place in nature with a little more humility and a little less hubris. Peter has many skills that humans do not possess. His sense of smell gives him knowledge of the past—what has just happened, even though it might be out of sight, and the future—what is invisible in the trees or around the corner and about to happen. That is one reason why his kind makes such good soldiers and security officers. Bacteria have mammals beaten in number of organisms, the diverse ecosystems that they inhabit, gross biomass, longevity on the planet, and prospects for the future. Non-avian dinosaurs were successful for 29% of total time vertebrates have existed. Humans with their paltry three million years hardly register on the same scale.
When we think about decision-making processes, it is useful to distinguish between systems of belief and systems of knowledge. Systems of belief are carried by cultures, and help members of those groups define their places in their milieu and distinguish them from others. It is perfectly fine to believe as part of your worldview that the Earth resides on the back of a turtle. On the other hand,
when making decisions about our common future, it might be a better adaptive strategy to rely on systems of knowledge, such as the fact that the ratio of carbon dioxide to oxygen, or the amount of methane in the atmosphere, matters to our future as a species. It might also help to think of humans not as manufactures of celestial intervention or even as an inevitable result of evolutionary progress, but rather as animals lucky enough to share the Earth with all other life forms, over which we hold extraordinary powers of destruction.
Thomas H. Wilson is Chair of the Arizona Humanities Council, and also the Director of the Arizona Museum of Natural History.