My boyfriend glanced at the title of this book and said, "Isn't it obvious?" While I wouldn't describe the concepts as obvious, I would say they make sense. I loved this exciting book! It has thought provoking ideas relevant to our lives, such as the relationship between population age structure and political stability, and uses the evidence to suggest a variety of ways we can achieve a more peaceful world.Ideas:Ingroup/outgroup instinct:"The instinctive predispositions of team aggression... the ability to recognize kin, the ultimate ingroup, is critical for social animals. It is a prerequisite for avoiding incest... underpins altruistic behaviors."Left to their own devices, young men cause instability:"Young men are the revolutionaries, the superstar computer programmers,the best athletes, the most courageous soldiers, the bravest mountaineers, the most creative musicians, but also the most vicious gang members and nearly all the suicidal terrorists... Relatively minor shifts in demographic trends can actually precipitate major political events and help to shape the course of history... population age structure can tell us a lot about a country's political stability... civil violence around the world in the late twentieth century found a sharp rise when the ratio of younger men aged fifteen to twenty-nine years old equaled or exceeded the number of older men in the population... CIA identified rapid population growth as the number one problem in national security. Until recently, population growth and age structure have been major driving forces behind violence, insurrection, and war. Age structure of a population accounts for about one third of the variables associated with the likelihood of warfare. In other social species [sea otters and elephants], older individuals provide an important counterbalance to the aggressive instincts of young males."On terrorism and its relationship between young men not having opportunities or anything to lose:Palestinians: half the population under age 15, unemployment is 40% and rising, chaste Arab society, few men have financial independence to marry: large pool of young men, lack of opportunities, sexual frustration: breeding ground for team aggression in the form of terrorism.[now-married terrorists] "didn't accept [terrorist projects] because they feared arrest and losing their new family. Marriage and having children had put them in a situation where violent, high risk actions no longer made emotional, economic, or evolutionary sense,and Black September collapsed."The pill is mightier than the sword: the relationship between birth control and political stability / socioeconomic mobility:"One of the most important things we can do for the safety and peace of the planet is to let women have control over whether and when to have a child. .. The ability of women to control their family size is often resisted by men. Controlling birth allows women to become more educated, opens up more opportunities, move up economically, slows population growth/fight over resources, produces fewer volatile young men. Women having a lot of children have a hard time getting them or their families out of poverty...As women are given the means to control their own fertility, family size begins to fall. What has been called a "demographic dividend" then begins to kick in. Savings rise as the cost of educating an caring for the next generation falls, and women begin to achieve social and legal equality as they are able to contribute more to the formal labor force, [for example] all the Asian "tiger" economies...Stalin, Hitler, Ceausescu, and Idi Amin were among the vilest and most cruel dictators of the twentieth century and each one took specific steps to restrict access to family planning and safe abortion."This book caused me to think about how we can affect the state of our world. In the past, I'd bet the correlation between the success of your progeny and the success of your ingroup was probably significantly higher than the correlation between the success of your progeny and that of humans as a species. In the modern world, this may no longer be true, and that may be why our instincts to define an outgroup based on language/physical appearance/ religion/location, to then kill these outgroup members, and to oppose female ability to control birth, these relatively short term greedy behaviors that had led to higher reproductive success for their carriers in the past are now causing a problem and may lead to the destruction of our species. In the past, it probably benefited your ingroup to have outgroups that lived in turmoil and violence, but this is probably no longer beneficial- it's no longer sufficient to just have peace within your ingroup- the world is too connected so that we have to work for peace in other people's ingroups too.The old definitions and ways of identifying one's ingroup are actually now erroneous or misleading. Just because someone lives far away or has a different language no longer means that they are not in your ingroup- their lives do significantly affect the quality of your life and your long term reproductive success, so their welfare should actually be important to you. This is not an easy leap for us to make. We're programmed for a less global world. We have many Stone Age behaviors that have turned out to be maladaptive for our modern global world. For example, eating as much sugar as possible used to increase your odds of surviving and passing on your genes, but in today's world this behavior actually kills you and decreases your probability of mating because many don't want to mate with fat people. If we can't even control a desire that has such an immediate and local impact on our own bodies such as choosing what we eat, how much harder will it be for us to coordinate to override our instinctive tendencies to form ingroups/outgroups and think long term- generations into the future? How much harder is it to choose not to fear and hate the foreign dude than it is to choose not to eat that cake?I'm often tempted to view any problem as fundamentally a technological problem. We have developed fake sugars so that we don't have to deny our ancient programming. Making communications technology widely available to everyone can allow us to connect in communities that make it harder for us to hate each other, and making birth control technologies available to more women will help us solve some population and ultimately political, socioeconomic, environmental issues too.However all this seems like a short term solution- unless we find an energy source that grows faster than we do, or unless it's more efficient to create our own energy than to take it from others, we will always jostle for resources. Even if one day we achieve optimal population growth we will still have wars over what type of people get to comprise that population, and then maybe some people will figure out that they are more likely to push out the other parts of the population if they grow their own part beyond what is optimal in the short term, since it could be long term optimal if it means they get to eliminate the other populations long term, suggesting that people probably oppose contraception for members of their ingroup but are fine with outgroups having contraception, putting everyone in a reproductive arms race.