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>.

Human emotion

It has been accepted for many years that all humans, regardless of culture, have the same facial expressions.  A smile is a smile and means the same thing everywhere.  However, a recent study of people's interpretations of facial expressions disagrees with this common wisdom.
Creating many computer generated facial expressions, the researchers asked recent immigrants to the U.S. and Westerns to interpret the faces.  The subjects responded differently, which means that facial expressions may not have the biological basis that we have long assumed.  This study needs more work (more participants) before this can truly change how we think about the emotions of humans, but it does hint to part of the problems we have when interacting with foreign cultures.


Read about it here

The Sun, and the Color of Our Skin

Of the many things we identify ourselves by, skin color seems to be one that is both obvious and persistent throughout history (whether for better or for worse).  We attribute a lot of things to the color of our skin.  We build communities, cultures and our identities around our skin pigmentation, but we are often slow to attribute this “important” aspect of our lives to the science and evolutionary principles that actually underlie it. 

While there have been many historical movements for and against varying skin shades, there always is little thought paid to the fact that skin color is very dependent on the ancient migration patterns of our ancestors and the ability our extinct primate predecessors to adapt to heat and sun exposure.  Some scientists believe that our very early ancestors had light skin, similar to that of chimpanzees.  However, their skin began to experience various pressures as they wandered out of the forest and began to populate the more sun-exposed savannas and fields.  In the harsher environment offered by the savanna, our ancestors experienced selection for more sweat glands and for the ability to spend more time foraging in the sun.

While most people recognize the existence of a skin color gradient based on global latitude, it wasn’t until tests were conducted by NASA in the 70s and 80s that we could for sure correlate the amounts of ultraviolet light that reach the planet’s surface with skin color.  These tests showed that areas closer to the equator received more ultraviolet radiation and those further from it received less, correlating with darker-colored skin near the equator and lighter skin away from it.  Furthermore it was found that skin color actually has a lot to do with the vitamins that humans receive.

 “Unfortunately” for the supremacists (of any kind), skin pigmentation has more to do with regulating ultraviolet penetration of the skin than it does with the capabilities and rights of a human.  Skin color adaptations have been shown to oscillate and occur rather rapidly on an evolutionary time scale.  Given this fact, it should be no surprise that they are currently changing and will continue to change as human migration is further facilitated by improved means of transportation.  We should also expect to see the effects of these adaptations on “displaced humans” who move to areas to which their skin is ill-equipped to handle the levels of ultraviolet radiation.  How do you guys think modern migration and spread of technology will affect the color of our future?

Skin color of indigenous populations vary with the levels of ultraviolet radiation they receive.

 -Matthew Moran

Jablonski, Nina, and George Chaplin. "The Evolution of Human Skin Coloration."Http://www.bgsu.edu. Bowling Green State University, 2000. Web. 15 Apr. 2012. <http://www.bgsu.edu/departments/chem/faculty/leontis/chem447/PDF_files/Jablonski_skin_color_2000.pdf>.

Kirchweger, Gina. "The Biology of Skin Color: Black and White." PBS. PBS, 2 Feb. 2001. Web. 16 Apr. 2012. <http://www.pbs.org/wgbh/evolution/library/07/3/text_pop/l_073_04.html>.

Antibacterial Hand Products. Potentially Dangerous, Decidedly Useless.

As the son of a bonafide germaphobe, I have become quite well acquainted with many of the different hand sanitizers currently out on the market. While I have certainly come to appreciate the smell of cucumber melon and isopropanol that follows my mother everywhere she goes, I certainly had to endure nearly the entire bouquet of scents that the different foam, gel, and liquid replacements to hand washing come in. One common factor present among all of these different products has really come to concern me, however, especially as I’ve learned more about evolution this semester.  The worrisome component of these solutions of course, is the proudly advertised “antibacterial power” that my mother particularly seems to love. As we’ve learned in this and perhaps other courses, the elimination of sensitive bacteria by the careless use of antibiotics opens up a competition-free space for resistant bacteria to reproduce more successfully, evolve, and propagate their drug resistance. This of course can have tremendously negative public health outcomes if these bacteria end up being pathogenic for humans. Alarmed, I began to ask myself, can antibacterial gels and hand soaps lead to the spread of drug resistant bacteria in the same way that antibiotics do? Epidemiologists warn, they can.

Bird Song

I generally appreciate birdsong as I walk around campus. However, I always find myself grumpily thinking about strangling a bird and eating it for dinner when they wake me up too early in the morning. But regardless of my annoyance, I usually walk around Houston fairly amused by the chattering that goes above my head in the form of song. But to my human ears, it all sounds like chirp chirp chirp, if you know what I mean.

So it was to my great surprise when I found out that birdsong has actually changed depending on the environment. In fact, the sheer difference between the city and a forest leads birds to have a change in bird song, and consequently in signaling. This divergence was noted in an article that compared the songs of great tits within the city and the forest where it found that songs changed both in duration and also in frequencies. [1]. The great tits in noisy locations (city) sing at a higher minimum frequency, most likely to be heard over the ever-present lower frequency white noise of the city. Furthermore, these birds in the areas with greater sound pollution had a restricted range in their repertoire of songs and

This study implies that an environment changed by humans can potentially alter the communication of a wild bird like the great tits. This amount of change in the communicative aspect for wild birds domesticated within a city can affect breeding opportunities and change a species' drastically. So while my own ears might be hearing chirp chirp chirp, the population of birds in a city might actually slowly be changing their own birdsong to something a little less diverse than expected in the wild, which might even alter mating behaviors in the future.

[1] Slabbekoorn, H. & Peet, M. (2003). Birds Sing at a Higher Pitch in Urban Noise. Nature. 424, pg 267.

I am a Great Tit!

from http://robandmazza.blogspot.com/2011/05/chick-  factor.html

See into these C-Sections

Recently I babysat for a couple who wanted a night out. As they told me about their precious little parasite, one thing that caught my ear was that she was a delivered through a Caesarean Section rather than natural birth. Through some medically related classes that I've taken at Rice University I've been hearing how there has been an increase in the amount of C-sections done. Although many attribute this phenomena to the availability and convenience of the procedure, I began wondering if evolution could actually be a major factor in this increase of C-sections.


Of course, research needed to be done and I scoured through Google Scholar and the Fondren Library for articles that could potentially let us see more clearly in this C-Section phenomena. Many articles concur that there has been rising rates in caesarean sections of approximately 10-15% in the World Health Organization [1]. However, delving specifically into the idea that evolution explaining an increase of c-sections, apparently one reason linked to evolution is that the human body is rather like a hunter-gather's body living in the 21st century. While society has changed so that women have become fatter (sigh) and more likely to give birth at an older age. However, evolution has not occurred through natural selection on women's' bodies to adapt to those social changes.  So ultimately, the article concluded, "cultural evolution has outstripped biological evolution."


I quickly dove back into the mess of articles to see if anything else corroborated these everyday evolution events happening in our very midst (well, not mine or yours, but "ours" as in humanity's). And I promptly stumbled upon another article at that discussed the conflict between the maternal pelvis and fetal head size in terms of selection pressure [2]. In this article, it was concluded that human birth has always been constrained by the size of the birth canal  and pelvis (oh lovely images), and that those babies with larger heads than normal before C-sections would die from cephalopelvic disproportion. Thus, pelvis size has always been a negative selection on the size of babies' heads.


The article goes on to speculate about the increase of IQ that might be seen in the future due to the introduction of C-section, and consequently the survival of big-headed babies.  However, I find myself a little skeptical about that. But who knows, maybe the baby I watched over recently is going to be a genius - after all, she did come from a C-section birth, the newest removal of a negative selection force.

 -Karen Lin


[1] Liston, W. A. (2003). Rising caesarean section rates: Can evolution and ecology explain some of the difficulties of modern childbirth? Royal Society of Medicine (Great Britain).Journal of the Royal Society of Medicine, 96(11), 559-61. http://search.proquest.com/docview/235006270?accountid=7064
[2] Walsh, J. A., M.D. (2008). Evolution & the cesarean section rate. The American Biology Teacher, 70(7), 401-404. http://search.proquest.com/docview/219029276?accountid=7064

Hominid Move from Trees to Ground

   Our presence living on the ground (or at least not in trees) is seldom remarked upon in everyday life, but our ancestors spent their lives in the trees. How did our species make the move from the trees to the ground? Following loosely from my last post about learning more about human bipedalism through the observations of a closely related species, a new study into the ground nests of chimpanzees has revealed some interesting possibilities about our ancestors’ move from the trees to the forest floor. 

  

Bipedalism in Humans and Chimpanzees

   One of the key identifying characteristics of humans is our ability and preference for walking upright on two legs. We tend not to think much of it in our day to day lives, but bipedalism is rare in the animal kingdom; only primates are capable of it and among primates only humans are bipedal to the exclusion of all else. But why did humans and other primates develop even limited bipedalism? Other mammals exist without it fairly well. There have doubtlessly been many theories about this trait, two are discussed below.

“Asian Flush,” a Gift or a Curse?

As anyone who has ever been to a Rice party can attest to, many of our friends from East Asian backgrounds tend to show a visible response to alcohol much more quickly than others might. While mostly thought of as nuisance, the pink facial tinting known as “Asian flush” or “Asian glow” is believed to have been evolutionarily selected as a favorable trait relatively recently in our biological history.

For those unfamiliar with “Asian flush,” the term is most commonly used to describe a wide range of symptoms that appear shortly after drinking alcohol. As the name implies, the most frequently experienced symptom of this is turning red in the face, though some report the occurrence of nausea, tachycardia, and facial swelling as well. These symptoms are produced as a direct result of an enzyme deficiency that leaves the body with an accumulation of one of alcohol metabolism’s first byproducts, acetaldehyde, which is the chemical culprit behind all of these unpleasant symptoms.