The limitations of geological periods, imposed by physical science, cannot, of course, disprove the hypothesis of transmutation of species; but it does seem sufficient to disprove the doctrine that transmutation has taken place through 'descent with modification by natural selection'. -- Lord Kelvin (Of Geological Dynamics, 1869).
It might seem odd that I start a post about evolution with a quote claiming natural selection is inadequate to account for the transmutation of species. It is, though, highly relevant to what I'm going to discuss in the post, and strikes at the heart of why it's fundamental for us to understand the theory of evolution by natural selection. See, in 1869, Lord Kelvin's position was fairly reasonable, and, as you'd expect for a man of such high scientific standing, the available evidence in physics did seem to conflict with Darwin's theory. The Sun was one particularly salient point of contention: to get the diversity of species we see on Earth, evolution needs a long time to work (on the order of hundreds of millions, if not billions of years), yet according to 19th-century physics the Sun could only have been burning for 40-million years.
We now know the Sun is powered by nuclear reactions, allowing for times far-longer than originally conceived by older models. The lesson of the story, and why I included it in the opening, is perhaps best captured with a single word: change. Change is, in fact, all around us, and, despite providing a tenuous opening to a blog post, it is very crucial to the world around us -- from the melting of ice to the creation and rejection of ideas. As you shall come to see, change is fundamental to evolution, not only through the mechanisms in which it acts, but also in its conception as an idea. An idea stretching back long before Charles Darwin was even conceived.
From the Antihero of evolution to the Great Chain of Being
Tracing the early ideas for naturalistic explanations of the world takes us as far back as early antiquity. The earliest recorded material belongs to ancient Greek philosophers, with the likes of Anaximander (c. 610--546 BC) and Empedocles (c. 490--430 BC) suggesting non-supernatural explanations for the origin of living things. Though, arguably, it was the philosophy of Plato (c. 428--348 BC) and Aristotle (384--322 BC) that came to dominate the age with two fundamental ideas: essentialism and scala naturæ.
First developed by Plato, who Ernst Mayr would later refer to as the great antihero of evolutionism, essentialism is the idea of observed objects in the real world being merely reflections of a limited number of essences: the attributes that fundamentally underpin what an object or substance is. The important point being that essences do not change. Instead, they are fixed, with any variation being the product of poorly translated reflections (a good way to think of this is to imagine a house of mirrors where one person represents the constant, unchanging essence and each individual mirror representing the variations of that essence).
More relevant to evolution is the second idea, scala naturæ, put forth by Aristotle who, partly based on his own emphasis of observing the natural world, derived a linear sequence of organisms from least to most complex:
Unlike the picture above, Aristotle's conception of the Great Chain of Being had humans as the pinnacle of creation, with plants occupying the lowest level. This teleological view of nature would later provide a profound influence on medieval philosophers, such as Augustine, who merged such views of nature with religion. Under this view, man was relegated to fourth on the chain (behind God, Angels and Demons), with Aristotle's discussion on the specific adaptations of organisms later being fundamental to St. Thomas Aquinas' argument from design: that the order and specified design observed in the living world provides evidence of an intelligent designer. There were plenty of other viable explanations at the time, from the speculations of Taoist philosophers, where species developed differing attributes in response to differing environments, to that of the Muslim Biologist, al-Jahiz, who speculated on the struggle for existence.
Nevertheless, it was the idea of an unchanging and eternal world, and Christianity's later introduction of an early creation, which held sway long-enough to serve as criticisms against Darwin's theory. Even in the 15th Century, when the Renaissance started spreading the early foundations of modern science, biology was still seen to belong in the domain of natural theologians and their belief that individual adaptations of organisms held some insight into God's immaculate design. However, progress was far from stagnant. In the 18th Century, the Great Chain was about to unfurl, largely thanks to Carolus Linnaeus' Systema Naturae, which established biological nomenclature through the grouping of species within genera and orders.
Life's Ancestry and an Older Earth
Under the mantra of God created, Linneaus organized, Linnaeus convincingly argued for a more naturalistic classification of animals, and, for the first time, placed humans together with other primates. Another fascinating aspect of Systema Naturae is its development from the first edition (1735), consisting of a modest eleven pages, to the massive three-thousand pages in the thirteenth and final edition (1767). At the dawn of the 19th Century, the Linnean method had become the standard form of biological classification, with life consisting of three kingdoms: Regnum Animale (animals), Regnum Vegetabile (Vegetable) and Regnum Lapideum (minerals). Furthermore, he also derived a classification based on 5 levels (all of which are still used today): Kingdom, class, order, genus and species.
As things were beginning to slowly develop in biology, geology was shifting into a far more dramatic pace with the discovery that sedimentary rocks were the product of ancient oceans. At the centre of this debate was an idea, made popular by Archbishop James Ussher's dating of biblical chronology, of the Earth being relatively young: created at around 4004 B.C. The conflict, then, concerned two different theories for the thickness of sediment observed. On the one hand were the catastrophists, where sediment layers are the product of a large-scale catastrophe, and on the other were the uniformitarians, who posited a much longer period of time than allowed by the Bible.
With new methods for dating rock strata, and the discovery of creatures no longer alive today, such as Buckland's Megalosaurus, meant the new geology was giving us our first glimpses of the history of life. In particular, it showed a trend where different groups appeared at successive stages through time -- first came fish, then reptiles, with mammals being the most recent. For much of this period the dominant consensus was that of catastrophe -- with the likes of Georges Cuvier arguing, on the basis of comparative anatomy, for a rigidity in species as opposed to evolutionary transformation. It was probably not until the publication of Charles Lyell's Principles of Geology did the consensus begin to shift towards uniformitarianism.
Lyell's view was that observable geological processes, like erosion and volcanic activity, could, given enough time, drastically shape the landscape. For instance, Lyell shows how a long series of eruptions, built up over a period of time, had built up Mount Etna in Sicily. The importance of Principles to modern Geology cannot be understated, but, for the purposes of this essay, our interest lies in how this book would come to greatly influence a young Charles Darwin, who saw analogous processes in biology: that, like the changing rocks, life developed through incremental changes over a long period of time. However, another part of Lyell's view, James Hutton's steady-stateism, meant he would largely remain in opposition to any future evolutionary theories, including the man we are now going to turn to: Jean- Baptiste de Lamarck (see picture below).
The First Evolutionary Theory
Social and economic progress in 18th Century Europe meant ideas about biological change were no longer deemed too outlandish to be considered. Pierre de Maupertuis suggested several ways in which dark-skinned humans came to be, whilst Linnaeus emphasized evolutionary transformations within genera, and Immanuel Kant speculated, on the basis of similarities between organisms, that they may have originated from a single, ancestral source. However, it was the French naturalist, Lamarck, who truly put forward the first comprehensive evolutionary theory, with the publication of Philosophie Zoologique in 1809.
Unlike some of his predecessors, Lamarck's did not see species as being these fixed and immutable creations. Instead, he asserted that species changed progressively along a linear Chain of Being; much of which was based on the continuous gradation he saw in fossil mollusks. He is perhaps most famously remembered for subscribing to certain claims about inheritance. At its most basic, the theory stated that organisms inherited characteristics they acquired over their lifetime. Couched in current terminology: changes in your phenotype are passed onto the next generation.
These ideas are quite different to what Charles Darwin would eventually propose, but the important point to take away is that Lamarck, and many others during this period, are starting to seriously think about evolution. Much of the reason for this rests in the steady accumulation of evidence, and, looking at the larger perspective, a greater appreciation of the sciences.
In the next post, I will finally get on to discussion Darwin's theory of evolution... After having touched upon two important precursors: Adam Smith and Thomas Malthus.
Reference: Barton et al (2007). Evolution. Cold Spring Harbor Laboratory Press: Cold Spring Harbor, New York.