On hearing I had an interview, two of my housemates, Ana and Jane, insisted they take me shopping for a new suit. It was a sensible call, as my clothes no longer fitted me. I wasn’t particularly domestic back then, and to get the washing machine going I simply turned the dial to the first setting, which turned out to be boil wash. I only learned of my mistake when Ana asked who was boil-washing their clothes, and I suddenly understood why they had become so tight. Under the sartorial gaze of Ana and Jane I bought a dapper suit, collared shirt and tie, and the next morning I headed off to my interview. I had to get from Sunningdale in Berkshire to north London in the rush hour, and this meant standing for most of the journey. As the train drew to a stop at Twickenham, the man standing next to me managed to spill most of his cup of coffee down my shirt and tie. Not a great start. Shortly afterwards I realized my journey planning was cutting things very tight, and a tube delay meant I had to run the mile from Camden Tube station to the Institute of Zoology on one of the hottest mornings of the year. I arrived drenched in sweat, coffee stained and smelling like a cross between Starbucks and a gym.
My interviewers, Steve Albon and Josephine Pemberton, gave me a few minutes to catch my breath before ushering me in. I was flustered and still sweating profusely, so much so that one of them offered me a towel to wipe my dripping forehead just after I’d answered the first couple of questions. Despite this, I must have impressed, for the following day I was offered the job. I had a three-year position at the Institute of Zoology to study the genetics and ecology of red deer living on the Isle of Rum in the Inner Hebrides and a breed of wild sheep living on Hirta in the St Kilda Archipelago, one of Britain’s remotest islands. Little did I know it back then, but I would continue to work on these two study systems for the next eighteen years. I became good friends with Steve and Josephine and many others who collaborated on the project, and I only stepped back from this study when a scientific disagreement over approaches threatened to jeopardize these friendships. I am pleased to say we all remained friends, and the move to work on other systems, including wolves in Yellowstone, guppies in the freshwater streams of Trinidad, and a small species of green bird called silvereyes that live on the islands off Australia, a study system my wife Sonya has worked on for over twenty-five years, proved to be a great decision.
In the years I spent working with red deer on Rum and Soay sheep on Hirta I became proficient in working with mark-recapture data, something I still do. To generate these data, individual animals living in the wild are humanely captured, often shortly after birth, and affixed with a unique mark. In the case of sheep, the mark is a numbered ear tag, for red deer it was an expandable patterned collar, in wolves it is a collar that sends out a bespoke radio signal that allows us to identify where the animal is, and in the guppies it is a tiny tattoo. After marking, animals are then released back into the wild at the same location they were captured, and each time they are subsequently seen or caught their location is recorded. Coupled with other data that are collected at the time of capture, including blood samples that allow family trees to be constructed for each individual, and phenotypic trait data on attributes such as body size, position in a dominance hierarchy, evidence of parasites, state of the animal’s dentition, and all sorts of other measurements, it is possible to study questions as diverse as the effects of climate change on wild animal populations, and why and how they evolved the phenotypic traits they have.
The reason I was so happy with my decision to work with guppies, wolves and silvereyes I quickly realized was that my knowledge of the natural world was very biased by what sheep and deer do. As I started to work with experts who had dedicated their lives to building incredibly valuable, individual-based studies of other species, I came to appreciate that each individual in each species really is unique, not just in its genetic code but also in how it lives its life. I would never have understood the way that nature works in as much detail as I do had I remained a sheep and deer expert. Those studies were invaluable for my training, and I will always be grateful for the opportunity to spend so long working on these systems. But it was the guppies, the wolves and the silvereyes that allowed me to flourish. Hours spent chatting with research collaborators in Yellowstone National Park, and with Sonya on walks with Woofler in and around Oxford or on visits to Australia, helped me break free from my narrow herbivore focus.
What I started to appreciate from working with each of these very different species is that individuals in each population experienced very different causes of death, and these causes mattered. Wolves tended to die in fights with other wolves or from disease; guppies that lived with predators would inevitably end up in the jaws of a predatory fish such as a goby, while those that lived away from predators would die from a lack of food; while Sonya’s silvereyes would often die during harsh winter storms, from disease outbreaks, occasionally from fights with other birds, or from unknown causes in old age. Just as important as the causes of death were events that prevented some individuals from breeding. In some cases, these events were a failure to lay down enough fat to produce offspring, or a failure to find a mate or breeding territory, or dominant individuals killing the young of subordinates, as happens in the wolves. Within each population, the major causes of death and failure to breed favoured phenotypic traits that reduced these threats, and by understanding what caused death and reproductive failure, and how different traits altered these risks, I could draw generalizations across very disparate study systems by linking their evolution and ecology. Natural selection is all about understanding how different phenotypic traits help individuals avoid things that can kill, while sexual selection focuses on how other phenotypic traits minimize the chances of failing to breed. Individuals with DNA sequences (genes) that code for the development of phenotypic traits that reduce the risks of death and reproductive failure leave more descendants. More descendants mean more copies of genes that code for the production of these beneficial phenotypic traits, and this means these beneficial genes increase in frequency within the population from one generation to the next. Evolution driven by this process has been continually ongoing since the first organism evolved.
Across the 3.9 billion years of the line of descent from LUCA to you and me, our ancestors have faced countless causes of death and things that could stop them reproducing and passing on their genes to the next generation. Yet each of our ancestors survived long enough to produce descendants, with evolution eventually producing us. The same is true for every other individual of every other species alive today. To achieve this astonishing feat, numerous challenges were faced and overcome, with evolution producing ingenious solutions to minimize the myriad risks our forebears faced. As the tree of life grew and life diversified, evolution moulded endless new phenotypic traits to help each species cope with the causes of death and reproductive failures that life threw at it. These phenotypic traits are coded in DNA, with the study of life’s most important acid having helped biologists piece together not just the tree of life but also much of its history.