DOMESTICATION AND HUMAN SELF-DOMESTICATIONThe term ‘domestication syndrome’ describes a range of correlated trait changes seen in domesticated populations when compared to their wild relatives or ancestors (Jensen, 2006; Wilkins et al., 2014; Zeder, 2015). Controlled experimental breeding has demonstrated rapid emergence of this syndrome in several mammal populations selected for dampened reactive aggression and stress response (Jensen, 2006; Kulikov et al., 2016; Trut, 1999). These results confirm findings of correlated change from longstanding observational research in domesticated lineages (Hemmer, 1990). Known traits include: docile behavior; reduced sexual dimorphism; reduced prognathism; smaller teeth; skeletal gracility; reduced brain sizes; altered oestrus cycles and fertility; floppy ears; elevated vocal communication; and altered pigmentation (Hemmer, 1990; Sánchez-Villagra et al., 2016; Wilkins et al., 2014). Many of these features are known to appear rapidly, as heterochronic shifts in ontogeny (i.e paedomorphism or neoteny), rather than as isolated and adaptive mutations (Belyaev, 1979; Trut, 1999; Jensen, 2006; Zeder, 2012, 2015). Heritable hypoplasia of neural crest cell-derived tissues provides the most widely supported proximate explanation for these observed trait correlations (Wilkins et al., 2014). Interestingly, several traits seen in bonobos (Hare et al., 2012) and in humans (Cieri et al., 2014; Groves, 1999; Leach, 2003; Thomas and Kirby, 2018) sugge...
Emiliano Bruner and Ben T. Gleeson, editado por A. Benítez-Burraco
Spending more time sitting on our butts isn't just a problem for obesity and heart disease. The shift to a more sedentary lifestyle has probably been bad for our bones, too. A pair of papers published today in the Proceedings of the National Academy of Sciences suggest that humans evolved lighter joint bones relatively recently in our evolutionary history as a response to changes in physical activity.
Human sprawl is usually a threat to wildlife, but birds buck the trend. Can we help biodiversity take wing in our suburbs?
The diversity of life in my yard and those of my neighbours seems to defy the fact that the loss of natural space to urban sprawl endangers plants and animals across the globe. Intrigued by how our presence simultaneously stimulates and threatens life, especially birdlife, I set out to discover what happens when we clear forests or pave fields to expand our living space. Together with my graduate students at the University of Washington and an army of technicians, I rose early each summer morning, beginning in 1998, and stood among the forests, suburbs and work places of Seattle and its neighbouring cities. For more than a decade, we used a standard research approach to count each bird heard or seen near us. And we caught and banded thousands of birds to track their survival and nesting success.
The first years of counting reaffirmed what I witnessed in my yard. The variety of birds in suburbs and exurbs was unsurpassed. Even the nearby forest reserves we used as ‘control sites’ – places where we expected nature to thrive – were less diverse than lightly developed areas. City centres were home to only a few species, as we anticipated, but even here birdlife was inspiring – peregrine falcons plied the skies, while crows and gulls ruled the streets. In the small fragments of forest left in and around subdivisions, some of the birds we counted were disappearing; however, others lived long lives in healthy and sustainable populations.
I am not claiming that suburban sprawl is the answer to our conservation prayers: many species of sensitive and rare birds could never survive in our ’burbs. Even fewer animals that crawl or walk, such as mammals, reptiles and amphibians, manage to live long among us. And, where terrestrial biological diversity is greatest – in the magnificent tropical rainforests – biodiversity is steadily lost with progressive development. But development can enrich local areas by providing what many tolerant species require. Although ensuring global diversity still requires that we leave undisturbed space elsewhere for sensitive species, even then, the political will to create such reserves depends on our experiences with local diversity.
In this way, we humans allow one group of birds with special needs to thrive in our midst: a guild of birds known as ‘secondary cavity nesters’. These birds usually breed and sleep in holes drilled into decaying trees by woodpeckers, but in cities they nest in the nooks and crannies in our buildings, street lamps and overpasses. Facilitating secondary cavity nesters such as wrens, tits and swallows enriches subirdia’s ecological web and, critically, tightly entwines people within it.
Birds that survive in cities and suburbs do more than simply take handouts; some evolve new actions and physiques that allow them to better exploit humans. For example, the Brewer’s blackbirds that nest around my house have evolved a new behavioural strategy syncopated to our own actions. These scrappy parking-lot specialists gather each morning just outside a nearby Costco store and queue up with shoppers before the doors open so they can fly inside and feed among the cafés and shelves. I suspect this is ordinary natural selection at work shaping the diet and behaviour of blackbirds through enhanced survival and reproduction.
Another process of evolution, recognised by Charles Darwin as ‘sexual selection’, is also at work in subirdia. The dark-eyed junco, often called a ‘snowbird’, is a small, ground-dwelling seed-eater, characteristic of subdivisions in the US. Typically, male juncos have two or three white outer tail feathers that contrast with the darker, charcoal grey inner ones. These white feathers are reliable indicators of a male’s aggressiveness and ability to defend his patch of earth from his rivals: in battle, those with the most white win. However, aggressive males are also less attentive of their nestlings, something that appears to be noticed by urban female juncos. In the city, where heat and food are readily available, the breeding season is long, and a female junco can produce many broods of nestlings – especially if her male is faithful and cares for one brood while she hatches the next. The result has been a gradual muting of the male city junco’s tail because birds that are less willing to fight and more skilled at tending young are favoured by females.
The response of birds to urbanisation is only just beginning. Humans began living in cities around 5,000 years ago. Today, more than half of all people are urbanites. As exploiters and adapters learn and evolve strategies to survive among us, I expect to see new and stronger co-evolved relationships between people and other city animals. As well as kindling a diverse urban biota, it might even create unforeseen species.
One of the world’s oldest and largest cities illustrates what the future might hold for birds. Crows, which are supremely intelligent and innovative, thrive in most northern cities. In Japan’s capital Tokyo, the jungle crow has developed an array of cultural traditions well-suited to city life. Some crows gather walnuts, but because their shells are too tough to crack open by beak, the crows place them where passing cars can become nutcrackers. Other crows that live in the inner city, where the sticks necessary for nest-building are rare, routinely pilfer clothes hangers that they bend and weave into unique nests.
Respecting your ecosystem might start with discovery and understanding, but it eventually requires manual labour. Degraded lands must be restored to more natural conditions. To discourage non-native invaders and encourage native adapters, pulling and patching often take the place of poisons. Humans benefit, too. Working to improve or sustain the ecology of local neighbourhoods lowers stress, builds resilience, and allows us to feel our place in the ecological system to which we belong.
