DEGRASSE TYSON: And now for some
final thoughts on living forever. The urge to not want to die is as natural as
life itself. But you should always be careful what you wish for. One day, it
just might come true. If, starting now, everyone in the world lived forever,
then Earth's current population of seven billion, which would, at its current
rate of growth, double in 60 years, would instead double in only 35. Take this
forward six centuries or so, and you have so many people on Earth that
everybody will have to stand up straight, just to fit on all the world's land
area. So that leaves interplanetary colonization as the only obvious next step
to accommodate such vanities. But not all planets are Earth-like. Actually,
none of the known planets, inside or outside our solar system, are Earth-like.
Which means if bio-mechanical genetic engineering is what grants you
immortality, then why not alter or enhance our organs in ways that allow us to
thrive under the exotic conditions of alien planets? And that could only be decades
away. There's just one catch. You need a space program capable of leaving
Earth entirely, rather than just driving round the block in Earth orbit. Until
then, our bodies may out-advance our access to space, making Earth a very
crowded place to come. And that is the Cosmic Perspective.
And now, we'd like to hear your perspective on this episode of NOVA ScienceNOW. Log on to our Web site and tell us what you think. You can watch any of these stories again, download additional audio and video, explore interactives, hear from experts and watch revealing profiles of our Web-only series, The Secret Life of Scientists and Engineers .
The most commonly used AAS in medicine are testosterone and its various esters (but most commonly testosterone undecanoate , testosterone enanthate , testosterone cypionate , and testosterone propionate ),  nandrolone esters (most commonly nandrolone decanoate and nandrolone phenylpropionate ), stanozolol , and metandienone (methandrostenolone).  Others also available and used commonly but to a lesser extent include methyltestosterone , oxandrolone , mesterolone , and oxymetholone , as well as drostanolone propionate , metenolone (methylandrostenolone), and fluoxymesterone .  Dihydrotestosterone (DHT; androstanolone, stanolone) and its esters are also notable, although they are not widely used in medicine.  Boldenone undecylenate and trenbolone acetate are used in veterinary medicine . 
Chimpanzees live in large multi-male and multi-female social groups , which are called communities. Within a community, the position of an individual and the influence the individual has on others dictates a definite social hierarchy . Chimpanzees live in a leaner hierarchy wherein more than one individual may be dominant enough to dominate other members of lower rank. Typically, a dominant male is referred to as the alpha male . The alpha male is the highest-ranking male that controls the group and maintains order during disputes. In chimpanzee society, the 'dominant male' sometimes is not the largest or strongest male but rather the most manipulative and political male that can influence the goings on within a group. Male chimpanzees typically attain dominance by cultivating allies who will support that individual during future ambitions for power. The alpha male regularly displays by puffing his normally slim coat up to increase view size and charge to seem as threatening and as powerful as possible; this behaviour serves to intimidate other members and thereby maintain power and authority, and it may be fundamental to the alpha male's holding on to his status. Lower-ranking chimpanzees will show respect by submissively gesturing in body language or reaching out their hands while grunting. Female chimpanzees will show deference to the alpha male by presenting their hindquarters.