Convergence on the ground above the ground under the ground

Convergence is pervasive, and moving from the animals let us take a particularly striking example from the plants. Consider two desert plants, one a cactus (Peniocereus striatus) that grows in the Sonoran Desert of Mexico, the other a type of spurge (Euphorbia cryptospinosa) from east Africa. Both are rather unprepossessing plants, straggly, and to the uninitiated, which the plant presumably hopes includes ravenous herbivores, look as if they are dead. Not only are the plants quite similar in...

Hearing convergence

Hearing, of course, depends on the transmission of vibrations, and their transduction into electrical signals that in ways analogous to sight and smell are interpreted as sound. For most of us hearing is almost as important as sight, and since the invasion of land by the tetrapod vertebrates, effectively beginning with an amphibian-like creature,288 this sensory modality to detect and track airborne sounds has been extensively developed.289 Yet the evolutionary evidence suggests that the...

Eyes of an alien

It is beginning to look, therefore, as if active, fast-moving, and at least in some cases intelligent animals opt for the camera-eye.64 So, too, we need to remind ourselves that commonalities of eye structure may lead to convergences in brain structure and the evolution of visual centres, which is at least the case within the mammals.65 Yet, so far as visiting aliens go the story more often looks to the immense cylinder, embedded in the cricket pitch, the hatch slowly opening, a hideous...

Io Evolution bound the ubiquity of convergence

It was a cold spring day, and the little boy had been out for too long, playing in the pond. The other members of the family were not paying much attention, and it was only with a start that the father first realized that the boy was no longer to be seen then with a surge of anguished alarm he saw that not far from where the boy had been wading something was now floating. All attempts at resuscitation were futile. With great sadness they left the ambulance as the metal doors closed. Swiftly...

Universal chlorophyll

At first sight the problem of addressing the question of evolutionary alternatives seems almost intractable. How can we begin to compare something of which we know nothing with that with which we are familiar Self-evidently, but also trivially, the history of life is unique,3 and perhaps the absence of extraterrestrial communication4 is simply because intelligence is just another evolutionary quirk. Yet constraints on the alternative possibilities and trajectories through time, at least in...

Honorary mammals

So building complex circulatory systems, peering at the world through a camera-eye, and employing intelligence with a large brain have all evolved convergently. We are, however, in pursuit of the humanoid, and I shall assume that the galactic equivalent is in some sense mammal-like. This may seem too bold a claim, but let us see. So far as the Earth is concerned, there is a simple natural experiment. What we need to do is find a landmass which the mammals have failed to colonize. There is an...

Attacking convergence

Such multiple evolutionary trials suggest that life is far from some sort of contingent muddle, yet the criticism might be levelled that they are either rather general, such as the example of the matrix of skeleton space, or very specific, good for an anecdote over a pint of beer in the Green Dragon but hardly of any real evolutionary significance. Some examples do indeed seem to be little more than curiosities, such as the Jurassic crustacean that is reminiscent of the trilobites,107 or a...

Jack the railway baboon

So, genes and developmental pathways are a very important part of the story, but in themselves they cannot provide the entire picture. Differences there patently are, but despite their sometimes momentous consequences it may be that from a molecular viewpoint the rearrangement of a gene or protein is trivial.83 Indeed, in some ways we hardly needed years of frenetic activity in this area of genetics and developmental biology to learn this. At a rather early stage of this research programme the...

Giving birth to convergence

The case of the kiwi is a useful reminder that despite sticking to eggs, many other non-mammalian vertebrates have adopted the system of ovoviviparity, in which the egg is retained in the mother prior to a live birth. The squamate reptiles (lizards and snakes) are particular masters of ovoviviparity Richard Shine estimates that in this group this type of reproduction has evolved independently approximately 100 times,141 while Daniel Blackburn suggests that overall viviparity has evolved...

The conceptualizing pancake

It is worth remembering that the scepticism of such people as Simpson and Beadle was set in the context of the beginnings of the exploration of outer space. In addition, it coincided with the growing interest in what came to be known as the SETI (Search for Extraterrestrial Intelligence) projects, galvanized by Frank Drake and others with the formulation of the now-famous Drake equation (which attempted to estimate the number of extraterrestrial civilizations23) and the OZMA Project (which was...

Convergent complexities

The behaviour of complex social insect societies, and specifically the army ants, is more than a digression. This is because the emergence of such biological complexity may be much more constrained than is sometimes imagined.51 At the least it is a reminder that carnivorous species can be more successful, at least in terms of colony size, than the farming ants (and, as we shall see below, termites). Success, as even the most jaded (if not jealous) scientist well knows, is relative. Size, we are...

Respiratory convergence

Despite the apparent ubiquity of convergence, there are some areas of evolution where the role of convergence would be expected to be minimal. Of these molecular biology is surely the prime candidate. It is not difficult to see why. As was discussed earlier, the combinatorial 'universe' of protein space is unimaginably vast, which suggests that the likelihood of navigating to the same 'destination' is exceedingly remote. In itself this may not be terribly important. The success of proteins...

The bricks and mortar of life

In tackling Simpson's challenge there are obvious questions at what level of organization should we begin At what stage do humanoids become inevitable Perhaps, as just mentioned, we can allow ourselves some basics, such as proteins and DNA. But then where So far as humanoids are concerned, perhaps our starting point has to be the great apes But here there are plenty of convergences, ranging from the tools of some New World monkeys to the social organization of dolphins. Perhaps we should start...

Mormyrid Fish Brain

Figure 7.11 Longitudinal section through the brain of a mormyrid fish. Note, in particular, the immense size of the cerebellum, which comprises all parts of the brain above the dotted line. The various parts of this hypertrophied structure include the remarkable valvula cerebelli Va , the central cerebellar lobes C1 to C4 , the crista cerebellaris Cr , the electrosensory lateral line lobe ELL , the transitional cerebellar lobe TL , and the caudal cerebellar lobe CL . Total length of the brain...

Info

Currey et al. in Proceedings of the Royal Society of London B, vol. 268, pp. 107-111, 2001, and also V. de Buffr nil and A. Casinos in Annales des Sciences naturelles, Zoologie, Paris, vol. 16, pp. 21-32, 1995. J. D. Currey 1999, citation is in note 28 , p. 3289. In his paper Currey also draws attention to the convergence between the teeth of the sea urchins on which see R. Z. Wang et al. in Philosophical Transactions of the Royal Society of London B, vol. 352, pp. 469-480, 1997 ,...

Key

gt 1 Jupiter mass gt 1-4 Jupiter masses gt 4-11 Jupiter masses gt 11 Jupiter masses figure 5.3 A sample of extra-solar planets, scaled to our Solar System and the size relative to Jupiter. An astronomical unit is the distance from the Earth to the Sun, and is equivalent to 1.49 x 1011 m. Data taken from websites given in note 33. unimaginable. As we shall see later Chapter 6 , this has not prevented speculation about possible forms of life, although such hypotheses are unlikely to be...

Returning the gaze

Yet, concerning the eyes there is an obvious difference.20 Vertebrates, including humans, use a camera-like arrangement, whereas the crabs employ the compound eye that is typical of most arthropods. Has the principal of convergence broken down Not at all, because it is among eyes that we find some of the most compelling examples. The existence of camera- and compound eyes reminds us, of course, that solutions to biological evolution need not be unique, but are simply very strongly...

The nonprevalence of humanoids

What we know of the social insects, and especially the extraordinary organization of agriculture and warfare among the ants, is striking both in terms of their convergence and in the almost alien nature of these complex societies. Certainly the jointed skeletons, the compound eyes, the miniaturized clones, and apparently robotic social organization are a familiar staple of science fiction. Suppose that there are advanced extraterrestrials will they be like us, at least vaguely hu-manoid, or so...

Giant brains

Coefficient Encephalisation

The many convergences documented in the last chapter, from the agriculture of ants to the vocalization of birds, are strong evidence that the evolutionary emergence of many complex systems is highly probable, if not inevitable. Yet the sceptic will still pause in thought. figure 9.1 Jack standing against the trolley with Mr Wide note the lever frame in the background. Photograph courtesy of Euan Nisbet, Royal Holloway, University of London. figure 9.1 Jack standing against the trolley with Mr...

Towards a theology of evolution

Let us suppose that I am an immensely successful biochemist, and happen to be engaged in experiments involving gene manipulation. A couple of years ago I was attending a conference - keynote speaker, naturally - when I fell into conversation with a curious individual, who for some reason seemed much older than he actually looked. As we talked, it seemed we were walking across a plain of infinite dreariness, but his voice, his demeanour, how can I describe it He knew all about our work, and as...

Converging on the ultimate

Neanderthal Burial

Giant brains, tool use, bipedality, and even a precision grip are not, therefore, specific to humans. To be sure, in our species they are each developed to a high order, but their independent emergence suggests that in principle there is no reason why they could not be similarly honed. Still, that does not rule out the possibility that the human lineage possesses unique features, which if lost by some chance would never be able to evolve again in the contingent turmoil of continuing evolution....

Universal rhodopsin

As it happens, a number of other proteins can act as light receptors, and they too provide some illuminating cases of convergence. Yet the rhodopsin molecule seems to offer various advantages as Russell Fernald156 has remarked, in the context of vision although an opsin 'is not the only way to detect light it has proven irresistible for use in eyes'.157 Rhodopsin is remarkably widespread, and apart from its near-universal adoption in the various visual systems this molecule has long been known...