Chapter 2: Biology’s Grand Narrative
We are reviewing the book: Is There Purpose in Biology? The Cost of Existence and the God of Love. By Denis Alexander. Chapter 2 is Biology’s Grand Narrative. In this chapter Alexander asks the question: “What happens when we look at the general features of biological evolution – the overall “grand narrative” – in the light of the claim that it is necessarily purposeless? What do we actually observe?” His first chapter point is that we observe increased complexity over time. The first 2.5 billion years things rarely got bigger than 1 millimeter across. There were no birds, no fish in the sea, no animals wandering around. Gradually, through photosynthesis and other factors complex and not completely understood, the oxygen in the atmosphere built up to the 21% levels of today. Another major transition came with the development of multicellularity. Once multicellularity evolves, there is a huge scope for increased specialization in cell functions and in the construction of organs. There is good evidence that multicellular forms of life have evolved many times independently from all three forms of single-celled life, the bacteria, the archaea (archaea constitute a domain of single-celled microorganisms. These microbes are prokaryotes, meaning they have no cell nucleus.), and the eukaryotes (an organism consisting of a cell or cells in which the genetic material is DNA in the form of chromosomes contained within a distinct nucleus).
Figure 1 from the book gives the example that Alexander is talking about. Multicellular volvocine algae first started appearing 220 million years ago. Somewhere at some time a single –celled alga divided and the two daughter cells remained embedded in a chemical known as a glycoprotein. So from now on this chemical binding meant that different cells had to contribute to the common good, at least as far as that organism was concerned. It is then possible to track through the fossil record what happened next. Different cells became specialized for different functions already by 200 million years ago. Some cells started specializing in motility, in movement, and so they had to sacrifice their own reproduction. As the author of a recent review comments: “The importance of cooperation, conflict and conflict mediation in the early stages of the transition is likely a general principle for origins of multicellularity” (Herron, M.D. 2009. Many from One: Lessons from the Volvocine Algae in the Evolution of Multicellularity. Communicative & Integrative Biology, 2:368-70).
Figure 2 from the book illustrates the main point in the present context that, taken overall, evolutionary history has seen a huge increase in complexity as assessed by the sheer diversity of plants and animals. It is the “big picture” which is so striking. Alexander quotes evolutionary biologist Sean Carroll from the University of Wisconsin-Madison in a Nature interview:
Life’s contingent history could be viewed as an argument against any direction or pattern in the course of evolution or the shape of life. But it is obvious that larger and more complex life-forms have evolved from simple unicellular ancestors and that various innovations were necessary for the evolution of new means of living. This raises the possibility that there are trends within evolutionary history that might reflect the existence of general principles governing the evolution of increasingly larger and more complex forms.
Alexander himself notes:
As we stand back and look at the sweep of evolutionary history, we see huge creativity in life, immense diversity, but in a highly organized way, in which the ways of being alive for both animals and plants are constrained by the physical necessities of living on a planet with light and darkness, with this particular gravity, with particular atmospheric conditions at particular times, with particular temperature ranges. So, given carbon-based life, there do seem to be only so many ways of being alive on planet Earth.
Alexander then brings out the second main chapter point that has come to light in recent decades; that of convergent evolution. Convergent evolution is the process in which organisms that are not closely related independently evolve similar features. It is often thought that evolution is a purely random process and that over the billions of years since life began the process might have gone in any direction, not necessarily resulting in the kind of intelligent life-forms we see on the planet today. The question of evolution’s predictability was notably raised by the late paleontologist Stephen Jay Gould, who advocated the view that evolution is contingent and unrepeatable in his 1989 book Wonderful Life. “Replay the tape a million times … and I doubt that anything like Homo sapiens would ever evolve again”. Gould also famously likened evolution to a drunk on a sidewalk staggering around in a random manner. Alexander takes up and unpacks the meaning of “random” and “chance” in Chapter 4, so I will wait for that chapter to have that discussion.
The person who has done the most in recent years to investigate and popularize the idea is Simon Conway Morris, Professor of Evolutionary Paleobiology at Cambridge. His research group has also developed the Map-of-Life website highlighting many examples of convergence. The site says: “The name “Map of Life” reflects the way that evolution has repeatedly arrived at, or converged upon, the same adaptive solutions from more or less unrelated starting points, as though evolutionary trajectories were following a metaphorical “map” to the same destination.”
In the chapter, Alexander spends some time discussing the development of “camera eyes” in cephalopods (octopuses, squid and cuttlefish), cubozoans (jellyfish), and vertebrates (i.e. humans). This website lists “10 Striking Examples of Convergent Evolution in the Animal Kingdom” which would include:
1. Ichthyosaurs and Dolphins
2. Sparassodonts and Cats
3. Phytosaurs and Crocodiles
4. Foxes and Thylacines
5. Hedgehogs and Echidnas
6. Hyenas and Dogs
7. Tapirs and Pigs
8. Hyracodonts and Horses
9. Mudskippers and Tiktaalik
10. Placodonts and Turtles
This brief section on convergence in eye evolution has only just touched the surface of a huge subject. If you live on a planet of light and darkness, you are very likely to get eyes at some stage of evolution. The adaptive advantages are huge and obvious. This even led Dawkins to suggest that evolution is “progressive”, a notion Darwin himself found problematic, Dawkins writes, “the cumulative build-up of complex adaptation like eyes, strongly suggests a version of progress – especially when coupled in imagination with some of the wonderful products of convergent evolution.”
In a commentary on Gould’s idea of ultimate randomness in evolutionary history, Conway Morris writes that it is:
… now widely thought that the history of life is little more than a contingent muddle punctuated by disastrous mass extinctions that in spelling the doom of one group so open the doors of opportunity to some other mob of lucky-chancers… Rerun the tape of history of life… and the end result will be an utterly different biosphere. Most notably there will be nothing remotely like a human… Yet, what we know of evolution suggests the exact reverse: convergence is ubiquitous and the constraints of life make the emergence of the various biological properties (e.g. intelligence) very probable, if not inevitable.
Two other major evolutionary products that seem to be ubiquitous are cooperation and intelligence. Another related striking feature of evolutionary history is the rapid increase in brain size in hominids that has taken place over the past 2 million years, in which the brain more than tripled in size from around 400 cc all the way up to an average 1300-1400 cc.
Alexander concludes that, as we look at the “grand narrative” of evolution, taken as a whole, the claim that it is necessarily Purposeless begins to look increasingly implausible. There is an obvious arrow of evolutionary time – from ultra-simplicity to incredible complexity. We cannot avoid the constrained features of the evolutionary process, dependent ultimately upon the laws of chemistry and physics. Constraint and convergence are all around us.
I think he makes a very strong case here… and he’s not done yet.