IT’S one of the biggest questions in biology: is the outcome of evolution deterministic and predictable? In particular, was the evolution of human beings, or something similar, inevitable?

Jonathan Losos, an evolutionary biologist at Harvard University, approaches this through the contrasting views of the late Stephen Jay Gould and University of Cambridge palaeontologist Simon Conway Morris.

Gould famously argued that if we “replayed the tape of life” we would get very different outcomes, because the pattern of evolution is unpredictable. In contrast, Conway Morris claims that convergent evolution – the idea that similar conditions produce similar adaptations – is “completely ubiquitous”.

Improbable Destinies focuses on the evidence underlying these opposing positions. However, chatty writing and an unclear structure mean that Losos does not explain the reasons behind Gould’s and Conway Morris’s ideas. Nor does he fully explore how their contrasting world views (Conway Morris is a devout Christian; Gould was a Marxist) influence their thinking.

Losos initially focuses on well-known examples of convergent evolution, such as the tendency of island animals – for instance hippos and mammoths – to become smaller than their continental counterparts. He also describes in some detail a series of experimental studies on lizards and fish that provide support for the centrality of convergent evolution, and thus for Conway Morris’s view.

But in the chapter on Richard Lenski’s ongoing study of bacterial evolution, Losos appears to switch sides. Lenski’s experiment began in 1988 and has, to date, involved nearly 70,000 generations and quadrillions of cells. Initially, the 12 identical lines of bacteria all grew faster and produced larger cells over the generations, so showed convergent evolution. But after around 31,000 generations, one line exhibited a unique adaptation – the ability to feed on citrate. Due to a series of random mutations, this line took a very different evolutionary path from the rest. Lenski’s attempts to encourage other lines to follow suit have failed. “So much for predictability and parallel evolution!” Losos writes.

Losos’s conclusion is that neither Gould nor Conway Morris is right. Faced with similar selection pressures, similar populations will indeed often produce convergent evolutionary outcomes. Even distantly related groups, such as marsupials and placental mammals, may do this – think of the marsupial and placental moles, separated by over 150 million years.

“Stephen Jay Gould argued that if we ‘replayed the tape of life’ we would get very different outcomes”

But the process isn’t ubiquitous. Sometimes, stuff happens and evolution goes a little crazy. In New Zealand, there were no terrestrial mammals (bats aside) until humans arrived, but in a striking example of non-convergent evolution, the islands’ birds did not evolve forms resembling mammals elsewhere that have a similar ecological niche and environment.

Alongside the widespread phenomenon of convergent evolution, life produces many unique forms. The human lineage is one such.

But before the reader can conclude that our uniqueness suggests we are the whole point of evolution, Losos plays his trump card: the duck-billed platypus.

This monotreme mammal has hair and a beak, and lays eggs. Like ours, its lineage is unique in the fossil record. Losos concludes that humans are no more the end-point of evolution than is the platypus, with its singular and slightly comical assemblage of characteristics. Not all evolution is convergent, he argues, and uniqueness does not imply destiny. That seems about right.

This article appeared in print under the headline “Playing dice with the animals”

“Everything has changed now the horse no longer has a key role in transport, warfare, food and sport”

NEARLY 60 years ago, Russian scientist Dmitri Belyaev began a remarkable experiment that still runs to this day. His aim was to selectively breed wild silver foxes to see if it was possible to bring about a similar transformation to the one that turned wolves into dogs. How To Tame A Fox, co-authored by US biologist Lee Dugatkin and by Belyaev’s long-term collaborator, Lyudmila Trut, is a charming account of this study, which has intrigued behavioural geneticists and evolutionary biologists for decades.

Begun in secret at the tail end of Trofim Lysenko’s devastating rule over Soviet genetics, Belyaev’s study was expected to take a long time to produce significant results, if it ever did. Although foxes had been bred in captivity for their fur since the end of the 19th century, they remained as bitey and cross as they had been all those decades earlier.

Under Belyaev’s leadership, Trut and her co-workers used standardised tests to identify the least aggressive animals, and then mated them together. Within three years, the foxes began to accept humans and breed slightly earlier in the year. After four years, one cub, Ember, wagged his tail when Trut approached the cage. After eight generations, curly tails appeared. A few years later, some foxes began to breed more than once a year.

These findings were significant. In On the Origin of Species, Charles Darwin wrote that in virtually every domesticated mammal species, certain characteristics often appeared alongside tameness: floppy ears, star-shaped forehead markings, multiple breeding periods and reduced, often curly tails. (Camels are an obvious exception, but they are so bad-tempered that they are arguably not tame at all.)

Belyaev became convinced that this revealed something about the genes involved in domestication. He put forward the rather vague notion that domestication involves a period of “destabilising selection”, affecting the hormonal control of development. Dugatkin and Trut recast this idea in terms of gene regulation, but it isn’t clear what extra insight into domestication this gives.

When Belyaev began the study, DNA’s role as the hereditary material in animals was only suspected. Now, whole genomes can be compared and scientists can study where and when genes are expressed. As well as a story of scientific determination, How to Tame a Fox is therefore also a striking description of how much science has progressed.

“Certain characteristics appear with tameness: floppy ears, forehead markings and curly tails”

Yet while the social context is informative and Trut’s memories are often heart-warming, I wanted more science. There are repeated references to how cute, loyal, irresistible and rambunctious the tame foxes are, but not one set of data showing the speed with which selection had an effect.

Only five pages are given over to summarising the molecular genetic data from the past decade or so, to no very great conclusion. The group has recently identified 335 genes that show differences in their activity in tame and control foxes, some of which affect hormone levels. But there’s little evidence that these same genes were involved in wolf domestication.

For the moment, the persistent reappearance of the same suite of characteristics in various domesticated species remains a mystery. The most likely explanation, as Belyaev suggested, is that they are all focused on prolonging infancy, leading to changes in hormones and behaviour. Strikingly, these changes aren’t seen in the line of aggressive foxes that Belyaev astutely set up in parallel to the domestication study. Those foxes are simply very, very cross.

After about 20 generations, the tamed foxes became truly like dogs: loyal and unbearably cute. It is now possible to adopt a tame fox – the substantial fee goes towards supporting the research project. After reading How to Tame a Fox I am very tempted, but my cats would object.

This article appeared in print under the headline “Taking a brush to nature”

“At every step, the book pulls aside the curtain, revealing to the public how science is done”

WHEN I was a psychology student in the 1970s, there was a widespread view that the study of consciousness was a passport to irrelevance. Now many scientists grapple with it and anyone who cracks the problem can certainly expect a call from Stockholm.

Philosophers have pondered the issue for millennia and, understandably, are not going to be shoved aside by newcomers armed with electrodes and MRI scanners. Michael Tye, however, is not a neuroscientist, but a physicist turned philosopher, who for the last decade or so has been considering the evidence we use to determine whether other organisms are conscious.

In Tense Bees and Shell-Shocked Crabs, Tye confidently applies his method to animals, plants and robots. Because there is no accepted measure of consciousness, Tye resorts to what philosophers do best: rigorous thinking and logical argument. “Animal consciousness,” he says, “is just animal experience.” For this to be other than tautology, it must mean that consciousness equals experience equals sensation. That would imply that the simplest sensory system, capable of responding to external stimuli and modulating that response (that is, sensing and learning), is conscious.

If provable, this would indeed be a strong solution to the question of consciousness, but it is not one Tye adopts. Although he peppers his argument with descriptions of various neurons and brain structures, he operates with an obvious rule of thumb (probably shared by many readers) that is linked to apparent degrees of neuronal complexity. Thus he considers all vertebrates conscious, although one of his criteria, the existence of a certain class of pain receptor, does not fully apply to cartilaginous fish. Tye recognises the problem but skips away, leaving it unresolved.

He also thinks that the best explanation of bee behaviour is that they are conscious, though he is less certain about Drosophila. Strikingly, he considers it “a great leap of faith” to think that worms, which do not have many neurons, can “genuinely feel pain”. (The phrase “genuinely feel” is oddly vague for a philosopher.)

“Strikingly, Tye considers it would be a great leap of faith to assume that worms can genuinely feel pain”

Tye highlights learning and behavioural plasticity, opening the book with the bold claim that a small dog that whines to be lifted onto an inaccessible bed has self-awareness because it knows it cannot reach its desire unaided.

But it is not clear why this dog is any different from the set of cockroach neurons studied in 1962 by Cambridge University neurobiologist Adrian Horridge. His experiment showed the cockroach “learns” to keep its leg out of electrified water to avoid a shock. This seems like a similar behaviour to that of the dog: the cells “know” what they want (in this case, to avoid shock). Tye does not discuss this challenging experiment; presumably he would class it as “unconscious learning”, a category he applies to a number of counter-examples, excluding them from his central argument without further discussion.

Frustratingly, Tye has not located his exploration of consciousness in an evolutionary framework. Instead, he seems to suggest that if a structure does something in a complex organism, then a similar structure must do the same thing in a simpler organism. But evolution alters function according to selection pressures. A more solid grasp of evolutionary biology would have nuanced Tye’s arguments and tempered his judgements, bringing them closer to those of most of the scientists he quotes.

This is an entertaining and stimulating book that may profoundly irritate many scientists; students should be warned that university science generally employs different kinds of evidence and argument than the philosophical approach used here. I hope Tye will collaborate with scientists on experimental tests of his views. That would be far more convincing than any amount of argument.

This article appeared in print under the headline “What else is conscious?”