Future evolutionary directions

Even a large global catastrophe such as a 10 km asteroidal/cometary impact would not spell doom for our species if we would manage to spread to other solar systems by the time the impactor arrives. We can, however, postulate a number of scenarios, short of extinction, that will test our ability to survive as a species. I will not discuss here scenarios involving intelligent machines or more radical forms of technology-enabled human transformation.

3.5.1 Drastic and rapid climate change without changes in human behaviour

If climatic change either due to slow (e.g., anthropogenic) or due to sudden (e.g., supervolcanic) causative agents is severe and the survivors are few in number, there may be no time to adapt. The fate of the early medieval Norse colonists in Greenland, who died out when the climate changed because they could not shift from eating meat to eating fish (Berglund, 1986) stands as a vivid example. Jared Diamond (2005) has argued in a recent book that climate change has been an important factor in several cases of societal collapse in human history.

3.5.2 Drastic but slower environmental change accompanied by changes in human behaviour

If the environmental change occurs over generations rather than years or decades, there may be time for us to alter our behaviours deliberately. These behavioural changes will not be evolutionary changes, at least at first, although as we will see the ability to make such changes depends on our evolutionary and cultural history. Rather they will consist of changes in memes (Dawkins, 1976), the non-genetic learned or imitated behaviours that form an essential part of human societies and technology. The change that will have the largest immediate effect will be population control, through voluntary or coerced means or both. Such changes are already having an effect. The one-child policy enforced by the Chinese government, imperfect though it is in practice, has accelerated that country's demographic transition and helped it to gain a 20fold increase in per capita income over the last quarter century.

Such demographic transitions are taking place with increasing rapidity in most parts of the world, even in the absence of government coercion. Predictions of a human population of 12 billion by 2050 were made by the United Nations in 1960. These frightening projections envisioned that our population would continue to increase rapidly even after 2050. These estimates have now been replaced by less extreme predictions that average nine billion by 2050, and some of these revised projections actually predict a slow decline in world population after mid-century. Demographic transitions in sub-Saharan Africa and South Asia will lag behind the rest of the planet, but there is no reason to suppose that these regions will not catch up during this century as education, particularly the education of women, continues to spread. These demographic transitions are unlikely to be reversed in the future, as long as education continues to spread. Recently the chief of a small village on the remote island of Rinca in Indonesia complained to me that all his six children wanted to go to medical school, and he could not imagine how he could send them all.

Accompanying the demographic transitions will be technological changes in how the planet is fed. If rising ocean levels cause the loss of immense amounts of arable land (including major parts of entire countries, such as low-lying Bangladesh), hordes of refugees will have to be fed and housed. Technology and alterations in our eating habits hold out some hope. Soy protein is similar in amino acid content to animal proteins, and its production has increased 400% in the past 30 years. This crop is already beginning to change our eating habits. And new agricultural infrastructure, such as intense hydroponic agriculture carried out under immense translucent geodesic domes with equipment for recycling water, will rapidly become adopted when the alternative is starvation.

Little will be done to confront these problems without a series of catastrophic events that make it clear even to the most reactionary societies and governments that drastic change is needed. These catastrophes are already beginning to throw into sharp relief current social behaviours that are inadequate for future challenges, such as a disproportionate use of the world's limited resources by particular countries and restrictions on the free flow of information by dictatorial governments. Societal models based on national self-interest or on the preservation of power by a few will prove inadequate in the face of rapid and dramatic environmental changes. I will predict that - in spite of the widespread resistance to the idea - a global governmental organization with super-national powers, equivalent on a global scale to the European Union, will inevitably emerge. As we confront repeated catastrophes, we will see played out in the economic realm a strong selection against individual and societal behaviours that cannot be tolerated in a world of scarcity.

Discomfiting as such predictions may be to some, the accelerating rate of environmental change will make them inevitable. If we are to retain a substantial human population as the planet alters, our behaviours must alter as well. Otherwise, our societal upheavals may result in long-term ecological damage that can be reversed only after tens or hundreds of thousands of years.

Scream and argue and fight as we may about how to behave in the future, our past evolutionary history has provided most of us with the ability to change how we behave. This is our remarkable strength as a species.

3.5.3 Colonization of new environments by our species

A third future scenario, that of the colonization of other planets, is rapidly moving from the realm of science fiction to a real possibility. More than 200 extrasolar planets have been discovered in the last decade. These are mostly Jupiter-sized or larger, but it is safe to predict that within years or decades Earth-sized extrasolar planets, some of them showing evidence of life, will be found. The smallest extrasolar planet yet found is a recently discovered mere5-Earth masses companion to Gliese 581 which lies in the habitable zone and is likely to possess surface water (Beaulieu et al, 2006). In view of the selection effects applicable to the surveys thus far, the discoveries of even smaller planets are inevitable.

This prediction is at variance with the argument presented by Ward and Brownlee (2000) that planets harbouring complex life are likely to be extremely rare in our galaxy. However, that argument was based on a biased interpretation of the available data and the most restrictive view on how planetary systems form (Kasting, 2001).

No more exciting moment of scientific discovery can be imagined than when we first obtain an image or spectrum of an Earth-sized planet with an oxygen-rich atmosphere circling a nearby star (soon to become possible with the advent of Darwin, Kepler, Gaia and several other terrestrial planet-seeking missions in the next several years). It is likely that the challenge of visiting and perhaps colonizing these planets is one that we as a species will be unable to resist.

The colonization of other planets will result in an explosive Darwinian adaptive radiation, involving both our species and the animals and plants that accompany us. fust as the mammals radiated into new ecological niches after the extinction of the dinosaurs, and the finches and land tortoises that Darwin encountered on the Galapagos Islands radiated adaptively as they spread to different islands, we will adapt in different ways to new planets that we explore and colonize.

The new planetary environments will be different indeed. How will we be able to colonize new planets peopled with indigenous life forms that have a different biochemistry and mechanism of inheritance from us? Could we, and the animals and plants that we bring with us, coexist with these indigenous and highly adapted life forms? Could we do so without damaging the ecology of the planets we will be occupying? And how will competition with these life forms change us? Will we be able to direct and accelerate these changes to ourselves by deliberately modifying the genes of these small populations of colonists?

If we are able to adapt to these new environments, then 10,000 or 100,000 years from now our species will be spread over so wide a region that no single environment-caused disaster would be able to wipe us all out. But our continued existence would still be fraught with danger. Will we, collectively, still recognize each other as human? What new and needless prejudices will divide us, and what new misunderstandings will lead to pointless conflict?

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