Chapter 13: Mutual Affinities of Organic Beings; Morphology; Embryology; Rudimentary Organs
This final chapter will bring together the ideas that I have discussed so far to show the way in which naturalists attempt to organize the natural world is shaped by the effects of natural selection. Naturalists constantly re-work their classification of the natural world searching for some ‘Natural system’ that will reveal the true pattern of creation.
The different levels of organization, kingdoms, orders, classes and so on, are nested within one another, and denote different levels of similarities between the species within them. It seems clear in my mind, however, that these nested groups are not the result of arbitrary organization, but are the result of the genealogical relationships between these species. In essence, all of the organisms in one kingdom share key characteristics because they originated millennia ago from a single ancestor.
This is clear in the way that external similarities and differences can have no effect on classification, such as the likeness between a mouse and shrew. Their different origins are understood from other characteristics, and they are classed in different families. At a basic level, despite the often vast differences between the males and females of a species in many characteristics, they are always classed as the same species by naturalists because of their shared descent. Classification is ostensibly about finding physical patterns, but in reality, traces species’ family trees, their shared descent.
One of the central ways in which naturalists develop taxonomies is by investigating the morphology or physical characteristics of organisms. They must differentiate between what are called homologous characteristics- shared between two forms because they have been inherited from a common ancestor; and analogous characteristics- similar because two forms have adapted to the same circumstances, such as the fins of whales and fish. Analogous traits are misleading in classification, while homologous traits are useful family resemblances.
Even across vastly different lifestyles and forms, the common pattern of bones in the wing of the bat and the fin of the porpoise reveals their common descent from their shared mammalian ancestor. This basic pattern has been modified in many ways to suit different purposes, bones elongated or shortened, reinforced or whittled down, but the initial blueprint remains clear.
Despite the differences between the adult forms of even closely related species, the developmental stages of organisms are strikingly similar. As a result, naturalists have long used embryos to delve deeper into the relationships between species. For example, the embryos of mammals still have gill-slits that are supplied by blood vessels, vestiges of their distant aquatic ancestry that are lost as the embryo develops. Domestic breeders have made clear that the peculiar characteristics of many animal breeds can only be seen in the adults, while the young are indistinguishable. It is these protected stages of life that remain unmodified, and retain the evidence of an organism’s ancestry.
Rudimentary body parts
Apparently useless organs are scattered throughout nature, and have thoroughly puzzled most naturalists. The finger-like ‘bastard wing’ on birds, the remnant teeth of young baleen whales, or the delicate pelvis of some snakes are argued by some to ‘complete the scheme of Nature’. How, I ask, if each species has been created to be perfectly adapted to its existence, can the use of precious resources such as calcium and phosphorous in teeth then lost in adulthood, be of use to a developing whale calf?
I argue, in contrast, that these rudimentary body parts reveal the effects of inheritance and modification in organisms. Previously useful parts have become useless, such as eyes in cave-dwelling species, and been lost through lack of use. Economy is always favoured under natural selection, and parts that are no longer useful are not worth maintaining, and if the can be co-opted for something else, then they might be modified. For example, in some fish the buoyancy-aiding swim bladder has become a basic lung.
Our classification system, therefore, is in essence a genealogy, the structure of which is revealed clearly in patterns of morphology, embryological features, and even discarded parts. Far from being a barrier to my theory, these idiosyncrasies reinforce the gradual process of inheritance and modification under natural selection.
‘all true classification is genealogical; that community of descent is the hidden bond which naturalists have been unconsciously seeking, and not some unknown plan of creation, or the enunciation of general propositions, or the mere putting together and separating objects more or less alike.’
Recapitulation and Conclusion
I cannot deny that there are many serious objections that can be leveled at my theory. I have tried to deal with each as fully as possible and any remaining limitations should not obscure the power of the theory in general.
My theory proposes that an infinite number of forms, linked together through common ancestry, have existed through earth’s long history. Yet, we can see only scattered sections of these chains of relationship. The geological record does not hold the complete library of forms that would provide an irrefutable support for my theory. We must accept that the record has been left incomplete by geological events, rather than that these forms never existed. We can only help to continue to gradually add to the broken picture we have so far.
Despite the difficulties, the facts of a struggle for existence, that variations in all organisms’ characteristics exist, and that beneficial variations are preserved are difficult to refute. Such beneficial variations have accumulated over generations, and deleterious variations have been excised through the death of those carrying them. This has resulted in the gradual transmutation of species’ forms and their continual diversification to adapt to the complex requirements of life and fill new places in the economy of nature.
The myriad variations in our domestic plants and animals have been selected through careful breeding to result in wonderful forms that are both useful and aesthetically pleasing to us. If Man can manage such feats in even a few generations, it is inconceivable that Nature, acting on every aspect living beings’ forms and behaviours through the bitter struggle for survival, should not be able to effect the most dramatic and unimaginable changes over vast time periods.
The idea of each species coming into being as an immutable act of special creation falls far short as an explanation of the natural world. The varieties within species are not idiosyncrasies within the natural order, but are themselves incipient species, in the very gradual process of diversifying into new forms that will eventually become new species and even higher groups.
The image of these accumulating differences and gradually diverging forms explains the structure we have placed on the natural world: a hierarchy of groups, nested within each other. It explains the otherwise baffling similarities of form between distant groups, such as the common pattern of bones in the limbs of bats, humans, porpoises and horses. These links of common ancestry are further supported by the findings of remnant organs evident in the embryology of organisms, like the gill slits in foetal mammals, as well as the geographical distribution of species. This theory of inheritance and gradual modification also explains why there seem to be no sudden changes in nature, which is rich in variety, but poor in innovation.
It is important to remember that Natural Selection acts to change organism’s forms in relation to the pressures with which they come into contact: competitors and living conditions. Organisms are not perfected for some abstract purpose. The result of this can be seemingly highly imperfect characteristics, such as the death of bees that sting.
All of these instances point to a scheme of Nature that we have almost intentionally misunderstood up till now. But why has there been this blindness, the obliteration of every mystery with the stamp of Special Creation?
On the idea that the world’s existence has been short, the slow processes I describe would be unable to produce enough variety. Our more recent understanding of the earth’s vast age, too great a time for us to conceive of, provides space for the accumulation of infinite variations of life forms over innumerable generations. The history of the world we understand at present has been only a fraction of the time that has passed since the dawn of life.
Those that attack my theory do so by highlighting the difficulties I have mentioned. Yet, never question the great central failure of Special Creation: how might species miraculously come into being from nothing? I think that the development of life through modification, diversification and extinction agrees far more closely with the laws of the world set in motion by the Creator himself.
Though my theory has unexplained difficulties, at root, it explains the heart of the matter of the origin of all species. I have no doubt that these gaps will be filled by those who come after me and that this knowledge will cause a revolution in our understanding of the natural world.
We will map the geographical history of the globe through the current distribution of organisms. We will see each species as the result of a history of invention, and our classifications will, in a sense, reveal the system of creation. Within this, the origins of man will also be elucidated. Not only the past and present of life, but an equally long and wonderfully complex future will stretch before us.
‘Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.’