Why Did Humans Evolve?

It is pretty well known that humans evolved from ape-like ancestors. But let’s ask evolution study’s most important question: why?  What traits caused humans to diverge into a completely new species from our primate ancestors?

The answer, according to University of Utah biologist Dennis Bramble and Harvard University anthropologist Daniel Lieberman, is the ability to run. Bramble and Lieberman concluded that modern humans (Homos) evolved from ape-like ancestors called Australopithecus because they needed to run long distances. Two million years ago, natural selection favored the Australopithecus that could run – perhaps because they could outrun predators, or more efficiently hunt animals or scavenge carcasses. Over time, the body shape of the Australopithecus changed as new body features that favored long-distance running were selected, giving rise to the genus Homo.

Humans evolved from apes because of the advantageous ability to run long distances.

 

 This theory contradicts the popular theory that running arose as a by-product of bipedalism in our already human ancestors. However, bipedalism was a trait that evolved at least four and a half million years ago in our ape-like ancestors the Australopithecus. This species walked on two legs, but it also retained the ape-like ability to travel through trees. It was not until three millions years after the evolution of bipedalism that our ancestral species began to run. Learning to run came at the cost of no longer being able to travel through trees, and marked a significant transition of our ancestors from ape-like to human-like. 

Walking does not explain the radical transformation of the ape-like body that occurred and resulted in humans, since our first walking ancestors were still markedly ape-like. As Australopithecus began to run long distances, their features transformed, eventually giving rise to Homo species. For example, changes to the head such as a flatter face, smaller teeth, and a shorter snout shifted the center of mass back so that balancing the head became easier while bobbing up and down during running. The detaching of the shoulders from the head and neck allowed rotation of the body while the head looked forward during running.

If running had not arisen, these features would not have changed and we might still be very ape-like today (more so than we already are)! Therefore, the evolution of running marked a key event on the evolutionary timeline of modern man.

-Author: Nupur Jain

References:

Lieberman, Daniel E., and Dennis M. Bramble. 2007. The evolution of marathon running: Capabilities in humans. Sports Medicine 37(4-5): 288-290.

Photo from: http://coasthillsrunningclub.com/

What Do Women Want?

Mate selection is a vitally important process both in the animal world and amongst humans. Selecting a sexual partner plays a crucial role in reproduction, and therefore evolution. Interestingly, the reverse is also true: evolution impacts our mating decisions. Evidence suggests that women’s mating strategies have been impacted by evolutionary pressures faced by our ancestors. When a woman chooses a partner, her decision is partially the result of several psychological factors, perhaps even ones beyond her awareness.

http://en.wikipedia.org/wiki/File:Man-and-woman-icon.svg

Research into women’s sexual strategies is conducted from the perspective of evolutionary psychology. Evolutionary psychology is a fascinating field because it explores the impacts of evolution beyond the physical adaptations that species display over time. The core assumptions of this field are that the mechanisms of the mind, like any other organ, have specific functional adaptations. Among these mechanisms are adaptations underlying women’s sexual behavior.

The criterion for sexual selection that would be most favored by evolution is reproductive success. One of the major challenges to reproductive success is the unusually high parental investment required for human offspring. By default, women must invest in their children for a nine month pregnancy, and for an additional ~2.5 years after that while breastfeeding. Beyond this, human children are generally not self-sufficient for many years, and require further care. For females in ancestral times, bi-parental care better ensured their own reproductive success. Children were much more likely to survive during when male parents showed investment in their offspring. Therefore, women have evolved to select partners who are more likely to be invested in their offspring over a long term. The fact that marriage or other partnership between parents is an almost universal human concept demonstrates that seeking long-term commitment is likely an evolutionary adaptation. 

 In addition, women appear to have adapted to seek men who can acquire resources for them and their offspring. In fact, in a study conducted by Li and colleagues, women demonstrated that in building an ideal mate, ability to acquire resources and intelligence were necessities, while traits such as personality and kindness were given less importance. This makes sense given that, at the time evolution was likely operating on sexual decision-making, acquiring resources such as food was more difficult, and dictated survival.

Women’s behavior, as almost any man will tell you, is diverse and complex. It cannot be boiled down to a few factors such as those listed above. Modern women are not the same as ancestral ones, and can make choices based on more than reproductive success. However, the particular evolutionary adaptations discussed above – finding long-term partners and choosing mates with many resources -are widely observed. This indicates that, in addition to the conscious considerations of partner preferences made by individuals, most women have underlying mechanisms of the mind that cause them to pick mates that would in an ancestral world guarantee reproductive success. 

-Author: Nupur Jain

References:

Li, N. P., Bailey, J. M., Kenrick, D. T., & Linsenmeier, J. A. W. (2002). The necessities and luxuries of mate preferences: Testing the tradeoff's. Journal ofPersonality and Social Psychology, 82, 947-955.

 

Pillsworth, Elizabeth G., and Martie G. Haselton. "Women's Sexual Strategies: The Evolution of Long-Term Bonds and Extrapair Sex." Web. <http://www.sscnet.ucla.edu/comm/haselton/webdocs/pillsworth_haseltonARSR.pdf>.