“Reptiles and amphibians are sometimes thought of as primitive, dull, and dim-witted. In fact, they can be lethally fast, spectacularly beautiful, surprisingly affectionate, and very sophisticated.”
David Attenborough, despite recurrent threats of retirement, remains quite busy as one of the world’s foremost naturalists. As the creative and intellectual force behind the greatest nature documentaries (arguably the greatest documentaries, period) ever made, Blue Planet, Life of Mammals, and the blockbuster triumph of Planet Earth, Attenborough has returned for one of his finest achievements. Life in Cold Blood has its focus upon amphibians and reptiles, cold-blooded vertebrates that have a generally primitive reputation. That particularly cruel people are described as ‘reptilian’ is a distinction not lost on Attenborough, for he seeks to make these misunderstood animals accessible to the viewer. From the quote above, he would seem to be anthropomorphizing snakes, frogs, and turtles so that we can see parallels with ourselves and as a result care about them. Quite the reverse is true – we are what we are as humans because our adaptations have roots in the amphibian order, from which the reptile order evolved, and the birds and mammals sprang forth from that. In the end, all branches of an evolutionary tree lie in parallel, and depend entirely upon the roots to exist.
All of his features will present their subjects within the context of a system, be it a particular region, adaptation, or ecosystem. This is far more useful tactic than that used by most nature films that will examine a species almost in a vacuum (Hippo: Exxxtreme Herbivore!) as the question at the end must always be – why should the viewer care? In Attenborough’s films, the answer is because the ecosystem in which these organisms live affect all living things. The subtext is always the elegant interactions of life within a system, and that system must include humans, despite our belief that we do not require a natural system to survive. One imagines the ultimate hell for any naturalist: a pure urban biome populated only by humans, the animals they eat, and the rats that eat the waste. That anyone would want this system is beyond belief; the world is headed in that direction as the extinction rate of all species has eclipsed that of the Cretaceous period, which saw the end of the dinosaurs.
LICB starts by examining the metabolism of a cold-blooded animal. The question is – if one is dependent upon the rays of the sun for body heat, is that a significant disadvantage compared to birds and mammals, which are able to tightly regulate their temperature? Thermal camera imaging illustrates this, as the reptiles and amphibians awaken as cool as the surrounding air, and show up as almost black on infrared. They struggle onto a rock, the sun alights, and their bodies absorb it and they become as bright as a burner. Cold-blooded animals require this heating periodically to continue hunting and/or evading their predators. Though this seems a crippling quality, it turns out to be astonishingly efficient. Mammals burn over 80% of their energy intake just to regulate their temperature, and so they must eat copiously. This leaves far less energy for migration, communication, and the crucial activity of reproduction. Reptiles and amphibians are far more efficient, then, and so use less food, and survive in greater numbers during lean times. If the weather is cruelly cold, some frogs can freeze solid until the spring. Rain frogs can remain in suspended animation below desert sands for weeks or years until the rains come, and they chow down, mate, and lay eggs within a day before the sun dries the desert to its former desolation. Predatory snakes like the African Rock Python can kill animals many times their size, and thanks to their efficient energy use, will not need another meal for an entire year.
Efficiency aside, cold-blooded creatures make for dynamic entertainment. There is every bit as much color as one would see in tropical birds, speed to hunt down any prey (monitor lizards outrun rabbits, and the black mamba can outrun you), and behavior one generally thinks of as mammalian in complexity. This makes sense, as reptiles and amphibians may be our evolutionary ancestors, but given an equal time period have achieved the same quality of diversity and sophistication as we have. Each episode will fill your screen with a riot of color, as well as provide much food for thought. Poison dart frogs, chameleons, and even some snakes rival any tropical bird for sheer display.
LICB is dense with fascinating stuff. The sleepy lizard of Australia gives birth to live young and mates for life; if one dies, the other will mourn beside the body for hours. Crocadilians are dedicated to their offspring, and will guard them carefully until they are fairly large. If an egg fails to hatch, the mother will gently break the shell and move the young to the water. In the Mediterranean, biologists have discovered a new evolutionary relationship that has changed one island in the last 20 years. The dead horse plant (present throughout the Mediterranean) looks and smells like its namesake, and so attracts flies as pollinators, which in turn attracts a lizard that eats the flies. The lizards on one island learned to eat the seeds of the plant, and the behavior was learned by all the lizards on the island. The seeds then germinate in the lizards’ feces, which are spread widely. Today, this island contains a massive population of these flowers, which are quite rare elsewhere. It is interesting to note that this symbiosis is based upon a recently learned behavior – most people think of reptiles as acting solely on instinct.
Though the documentary is immensely entertaining, it is clear that Attenborough is on a desperate mission to generate an understanding of the natural world, and to impress upon the human population that it does indeed exist inside a system that requires responsibility. People do not have a fundamental concept of an ecosystem, let alone the awareness that we reside within one. As long as humankind believes it exists outside of nature, and is not dependent upon it for survival, it will continue to dig its own grave as a species. For example, the damage done to natural habitats in temperate zones and possibly our effects on climate change have caused a decrease in bee populations. We have little reason to care, except that bees perform US$1-2 billion per year worth of pollination of agricultural crops. So who is going to pollinate individual flowers by hand? As another example, the horseshoe crab, a lifeform over 600 million years in ancestry, was nearly destroyed by aggressive harvesting and beach destruction. This would have exterminated the only source of lysate, which detects bacterial infection within IV medications, and has saved over a million people who would otherwise have died from lethal blood infections. Even those species with no discernible use to human industry are of unknown value, for our efforts to understand Earth as an ecosystem have only just begun.
This lesson becomes clear in the chapter on amphibians, a group under threat from habitat loss and disease. A creeping fungus is moving through Latin America at 20 miles per year, and kills every frog in its area, forcing scientists to capture all they can for protection until some counter to the disease is developed. The fungus comes from another continent, spread by ships, and is spreading quickly due to global warming. Frogs are basic to any ecosystem as both predator and prey, which guarantees the collapse of other species if they are wiped out entirely. Given our relative ignorance of how these systems work, humankind will allow these catastrophic losses to occur at their peril.
If this is all for naught, and we fail to learn from such extraordinary lessons as presented in Life in Cold Blood, then the human race is doomed as a species. The only advantage humans have is our ability to learn, control our environment, and most importantly, to control ourselves.