Why Ida fossil is not the missing link

On May 19, 2009 a 47-million-year-old fossil was revealed to the public for the first time. This primate, nicknamed “Ida” was proclaimed by the media to be the “missing link” in human evolution and showed great promise in the quest to understand our species’ past. However, as the first descriptions of the fossil were released the excitement dwindled as scientists realized that the missing puzzle piece was still a mystery.

            Ida has been found to be a “new genus and species of adapiform primates, Darwinius massillae.” While Ida is clearly a primate, she lacks certain characteristics that would put her in the Homo sapiens lineage. She is therefore not a close relative to anthropoids, the group of primates that include humans, monkeys, and apes.

Adapiforms, such as Ida, did not have grooming claws or toothcombs. Despite the lack of these characteristics, Ida’s anatomy is very similar to the living lemur. As seen in the diagram above, her new lineage broke away from lemurs about three million years after lemurs evolved. Despite the controversy surrounding Ida’s relatives, her well-preserved form is very enlightening. Her stomach contents as well as some details of her soft anatomy were well preserved. While Ida is clearly not a link in our side of evolution, she may turn out to be a “missing link” between certain species of Eocene adapiforms.

More recently, the discovery of a fossilized jaw bone has subtracted some of Ida's excitement. In 2009 a 4.4 million year old fossil thought to be a human ancestor was found. Called Ardipithecus, this fossil was intact with complete fur and skeletal framework. This discovery has caused a lot of debate about its relevance to human evolution as some people are skeptical about where it would fall in the evolutionary timeline.

Personally, I find both discoveries intriguing and questionable. Other than the fact that we will never truly know the origins of the human species, it is hard for me to believe such a simple looking creature could have evolved into the blog writing "intellectuals" that we are now. As with Ida, Ardi will help to fill in a missing puzzle piece from the past, but it will never be proven that she is that closely related to you and I. 

Sources: Beard, Chris. "Why Ida fossil is not the missing link." New Scientist. n. page. Web. 22 Feb. 2013. <http://www.newscientist.com/article/dn17173-why-ida-fossil-is-not-the-missing-link.html>.

Weiss, Ken, Anne Buchanan, Holly Dunsworth, and Dan Parker. "A Chimp in Our Ancestry?." Mermaid's Tail. n. page. Web. 23 Mar. 2013. <http://ecodevoevo.blogspot.com/2009/11/chimp-in-our-ancestry.html>.

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Jogging Our Memories

            It’s no secret that regular exercise maintains and improves a person’s internal and external fitness, but new hypotheses, discussed in a recent article by The New York Times, are emerging concerning the extent of advantages that exercise can bring – and may have already brought – to the human body. Walking is one of the key traits that researchers in the past have used as evidence for human evolution, acquired after human ancestors diverged from the ape lineage. Usually, their diet and collaborations with others to hunt for food are the factors used to explain how humans continued to evolve, but now, researchers suggest that endurance running could have also had a major impact in how humans changed over time (Bramble and Lieberman, 2004).

In their paper, Dennis Bramble and Daniel Lieberman discuss how humans’ ability to endurance run – and do so with relative ease – is impressively much greater than any other comparable quadrupeds. Humans use much more metabolic energy while endurance running in comparison to other mammals; biomechanical research within humans today shows that their skeletons, long tendons in the legs, core stability, and ability to maintain a regular body temperature would have made running easier (Bramble et. al, 2004) and increased their chance of selection for future generations. But how does endurance running relate to human evolution? Bramble and Lieberman suggest that the ability to endurance run would have made it easier for early, scavenging hominids to gain access to prey. As hominids evolved into hunters and gatherers, endurance running capability grew more important. As with early hominids, those who were able to outrun (and catch) prey the longest, were more likely to be able to support their protein-rich diet, survive longer, and be more successful in passing on their genes to the next generation (Reynolds, 2012). However, these suggestions still don’t speak as clearly to how exercise may have aided human evolution in the past.

In another paper referenced by The Times, researchers David Raichlen and John Polk discuss the link between endurance running in human ancestors and the evolution of the brain. In line with the fact that humans can run longer than other comparable quadrupeds, we also boast brains that are three times larger than expected (Raichlen and Gordon, 2011). In recent studies, improved acuity and an increase in specific areas of the brain were linked with extended exercise. From experiments in rodents subjected to long bouts of aerobic activity, researchers saw a significant increase in brain-derived neurotrophic factor (BDNF), a protein that fosters brain growth and development. Other proteins such as insulin-like growth factor I (IGF I) and vascular endothelial growth factor (VEGF) also contribute to brain growth.

 Figure from Raichlen & Polk, 2013: “Evolutionary model linking APA and brain size in humans. Solid arrows denote downstream effects of selection for APA performance. Dashed arrow indicates a possible adaptive link between neurobiology and exercise performance.”

All these experiments and research suggest that as early humans ran for long periods of time after their prey, they were also slowly contributing to the evolution of the brain, shifting the species into a more streamlined and intelligent one than before. The long periods of aerobic exercise would have not only increased their fitness so that those genes could pass on to subsequent generations, but would have also increased proteins in the body that allowed the brain to grow. As the brain grew, humans became more cognizant and intelligent concerning increasingly complex matters.

So for those looking for encouragement in keeping up with their new exercise regimens, researcher Daniel Lieberman is correct when he says “there is a deep evolutionary basis for the relationship between a healthy body and a healthy mind” (Reynolds, 2012).

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Cited Sources:

Bramble, D.M., & Lieberman, D.E. (2004 November 18). Endurance Running and the

Evolution of Homo. Nature, 432(7015), p. 345-48.

doi:http://dx.doi.org.ezproxy.rice.edu/10.1038/nature03052

Raichlen, D.A., & Gordon, A.D. (2011 June 22). Relationship between Exercise Capacity

and Brain Size in Mammals. PLos One, 6(6).

doi:10.1371/journal.pone.0020601

Raichlen, D.A., & Polk, J.D. (2013 January 7). Linking brains and brawn: exercise and

the evolution of human neurobiology. Proceedings of the Royal Society B, 280(1750).

doi:10.1098/rspb.2012.2250

Reynolds, G. (2012 December 26). Exercise and the Ever-Smarter Human Brain. The

New York Times. Retrieved from http://well.blogs.nytimes.com/2012/12/26/exercise-and-the-ever-smarter-human-brain/.