Upright Origins

Evolutionary studies have conclusively demonstrated that humans and the great apes originated from a common ancestor, some six million years ago. In fact, DNA analyses show that we share some 98% of our DNA with chimpanzees and bonobos. We are close cousins.

So why do Homo sapiens stand upright on two legs, while our ape cousins hunker down closer to the ground, getting about on four legs? While we began running around on the ground on two legs, they maintained the ability to negotiate their way through the trees with strong forearms. Our forearms, on the other hand, morphed into appendages capable of carrying things around, while theirs maintained the ability to swing from tree to tree.

It has become an acceptable idea on the part of anthropologists that at some time in the past—some four million years or so ago—the vast forests of Africa transitioned to vast savannas of grasslands, punctuated by occasional trees. What's a tree-swinging ape to do, when the trees become spaced too far apart to enable it to swing from one tree to another? Well, it comes down to the ground and forages for food there, adapting to the new environment.

The threat on the ground, however, is that now lions and tigers find you at their level—providing them a new tasty treat. Lions love the savanna, which gives them the opportunity of chasing down prey that cannot leap into a tree to escape their charge.

Evolution, ever on the march for one species to be eaten and another to avoid being eaten, transformed our ancestors into critters who could stand upright, so they could better spot a lurking lion, and survive another day. Those savanna grasses could be peered over by ancient upright Homo erectus, giving them a survival advantage. In the meantime, chimps retreated to dense stands of trees along rivers, while our direct forebears came to preside over the open savannas. Not only could we see better in our elevated stature, but our arms were now available to carry food, weapons, and babies.

So what brought about the transition from dense forests to wide-open savannas? Climate change of some sort probably did it. Over the last several million—or even billion—years Earth's climate has spectacularly fluctuated. The causes of change have been diverse. We are often not sure of the origins of climate variation, although we can demonstrate that it did happen and describe the consequences.

Now comes the results of a recent fascinating study at several US universities suggesting that a series of supernovae in our corner of the Milky Way Galaxy showered the Earth with cosmic rays a few million years ago. For quite a long period of time these rays ionized the planet's atmosphere—causing it to be far more electrically conductive. The result could have been an increase of wildfires triggered by lightning in African forests, transforming the terrain from forests into grasslands. With trees much more scarce, grasses took over, and it's an advantage to stand above the grass, to spot those hungry lions.

So, were exploding stars the trigger for Homo species to become dominant? We know that, without supernovae, elements heavier than hydrogen and helium would never have been created in the early universe. Thus, it's true that we are all stardust—from rocks to plants to animals. Maybe we humans even owe our ascendancy to those exploding stars?

Whale of a Cousin

Only three species on planet Earth have evolved the process of going through menopause—wherein females continue to live many years after they have stopped reproducing. Two of these species are whales (killer whales and short-finned pilot whales) and the third is humans. For these three menopausal species, females quit reproducing in their 40s, but can continue living into their 90s. 

Why are these three dissimilar species so similar in this way? What could be the reason for menopause—or what is its advantages for a species—when the usual drive for a species to survive is to reproduce as much as possible, as long as possible, and pass their genes into the future? (If there was no reproductive advantage to menopause, it would not have evolved.) What use can old females have to their whale pods or human societies? Do we really need “old ladies”?

None of the great apes—with whom we share about 99% of our DNA—go through menopause. Old female apes stay fertile all their lives and live only to about 40 years of age. So again the question arises, why do old-lady whales (much more distant from us, DNA-wise) and humans quit having babies? I find it fascinating that it’s just the whales and us.

The answer of “why menopause?” seems to be due to the social structures that have evolved for these two types of mammals—structures that are unique to killer whales, short-finned pilot whales, and Homo sapiens. There are likely two answers as to why menopause is useful: (1) keeping female elders around is important because they can share their knowledge and expertise of how to find food and safety, thereby continuing to help the species thrive, and (2) by giving up having more offspring, they can avoid reproductive competition with their daughters—so as to give the grandchildren of these long-living species a better chance at life. 

Continued survival of the species is what it’s all about. Resources in a group’s environment may be limited, so overcrowding does not help the species stay fit and robust.  Older females who quit having babies help to limit crowding. Additionally, useful and novel gene permutations (which younger females are more likely to create) must be allowed a chance to propagate into the future, which creates evolutionary progress.

So the grandmother humans and whales willingly and wisely step aside, passing the reproduction game on to their daughters. Crones can be an invaluable source of community knowledge and tradition. 

Males of these species can also possess valuable knowledge, but the females are more socially connected and pass more information on more effectively.