In Chapter VIII ("That's Life: Why You and Your iPod Must Die", from pages 194 to 205, Dr. Moalem discusses the issues inherent in human childbirth, explaining that two evolutionary changes to human skeletal structure has created difficulties for females when giving birth: bipedalism (walking on two feet), which has caused the pelvis and birth canal of women to become narrow and curved; and larger brains, which cause infant heads to be large, making it difficult for the baby to exit through the vaginal opening. This relates directly to Big Idea 1: The Process of Evolution Drives the Diversity of Life, as the question Dr. Moalem raises is simple - if these were evolutionary measures, why do they make it harder to reproduce.
Dr. Moalem goes on to briefly explain the aquatic ape hypothesis, which is used by modern evolutionary revisionists to explain these evolutionary changes. In a few sentences, explain what the aquatic ape hypothesis is and what evidence is used to corroborate it (this should be done at a rudimentary level; a middle schooler should be able to follow the logic). Using terms from the biology unit and the concept of natural selection, create a timeline (dates not necessary) that describes the evolutionary path supposedly taken by mankind under the aquatic ape hypothesis and state why such changes were necessary. Finally, provide examples of one or two other mammals that have supposedly undergone similar terrestrial evolutionary changes (i.e. from land-to-water or from water-to-air, etc.). Provide evidence for this/these changes and cite the sources from which you drew.
Be sure to include the following terms in each of the three parts delineated above: natural selection, selective pressure, survive and reproduce, selective advantage.
(Justin Millman; jmillma4@students.d125.org)
Part 1
ReplyDeleteThe aquatic ape theory resulted from the fact that many human ancestors spent time in and around water for survival. As Moalem mentions, "their ability to survive on land and water gave them twice as many options to avoid predators" (199). The aquatic ape theory could explain many features we humans have today. For example, it explains why we lost fur, why our noses are more prominent, and also, why fat is attached to our skin. All of these previously mentioned traits occurred in order to help us survive in aquatic environments- to streamline faster, to dive better, and to use less energy to swim.
This process of acquiring favorable traits is known as natural selection, which relates to Big Idea 1, which states the process of evolution drives the diversity and unity of life. In natural selection, first their must be variation in traits among a population. Then, due to selective pressures, one trait is favored over the other. This allows those with the selective trait to survive and reproduce better than those without the selective trait, thus giving a selective advantage to those with the trait. Over time, the population can adapt to its environment and will be able to survive and reproduce more easily.
In humans, "water acted as an agent of selection" (201). Humans could survive and reproduce better when able to use water to hide from land predators and also to dive for food. Therefore, humans with little hair, more prominent noses, and more fat were selected for in this environment. As time went on, the population of humans evolved to be able to use water to their advantage. The selection of bipedalism also arose, leading to advantages in the water, by being able to stand and breathe while in deeper waters. However, this also causes an issue in childbirth. Bipedalism changed our pelvis and twisted the birth canal making childbirth much harder, especially with human's bigger brains. To fix this, water birthing became a solution. Since water made it easier for aquatic apes to give birth with small pelvic openings, the same should work with humans. Thus, helping humans survive and reproduce.
(Posted by Lindsay Pontello, lpontel4@students.d125.org)
Part 2
ReplyDeleteOn the other hand, the savanna hypothesis suggests that our ancestors moved into the savanna and had to find new ways to live. In order to live in this environment, they had to "scan horizons for predators" (197), which lead to bipedalism, work together, which lead to bigger brains, and try not to overheat, which led to the loss of fur. The savanna theory is the conventional theory and can be proved true in numerous situations, however, there are many gaps in the hypothesis, allowing the aquatic ape theory to hold true in situations as well. The History Planet (http://historyplanet.wordpress.com/2010/03/17/aquatic-ape-theory/) acknowledges that the aquatic ape theory is far from proven, but provides significant evidence for its validity. The History Planet mentions that "Of all man’s ancestors, Home Erectus, experienced the largest singe brain growth. Most Homo Erectus finds have been found along coastal areas and Erectus is accepted by mainstream archaeology to be a shore dweller" This idea of living by the shore and having bigger brains supports the Aquatic Ape Theory rather than the savanna hypothesis which thought that since the apes had to make tools in the savanna, they adapted to having bigger brains.
A mammal that has supposedly undergone an change from being a land mammal into an aquatic animal is the whale. On http://darwiniana.org/landtosea.htm, a cladogram is shown from the book Evolution: The Triumph of an Idea by Carl Zimmer, displaying the transition from mesonychids (a land mammal) all the way to the odontocetes (an aquatic whale). Not only did the legs become flippers or vestigial structures for the whale, but the whole breathing and hearing systems changes (http://darwiniana.org/landtosea.htm). Once an aquatic animal, whales no longer had to worry about gravity and strength of bones, so evolution selected for whales to become the size they are today.
(Posted by Lindsay Pontello, lpontel4@students.d125.org)
Thanks, Lindsay. Discussions on the so-called “aquatic ape theory” are often outdated, not considering the recent literature on the subject.
ReplyDeleteHumans didn’t descend from aquatic apes, of course, although our Pleistocene ancestors were too slow & heavy for regular running over open plains as some anthropologists still believe.
Instead, Homo populations during the Ice Ages (with sea-levels often 100 m lower than today) simply followed the coasts & rivers in Africa & Eurasia, eg, 800,000 years ago, they even reached Flores more than 18 km overseas.
- google “econiche Homo”
- google “aquarboreal” on ape & australopith evolution
- eBook Was Man more aquatic in the past? introduction Phillip Tobias http://www.benthamscience.com/ebooks/9781608052448/index.htm
- guest post at Greg Laden’s blog http://scienceblogs.com/gregladen/2013/01/30/common-misconceptions-and-unproven-assumptions-about-the-aquatic-ape-theory
- http://greencomet.org/2013/05/26/aquatic-ape-the-theory-evolves/
- Human Evolution conference London 8–10 May 2013 with David Attenborough, Don Johanson etc. www.royalmarsden.nhs.uk/education/education-conference-centre/study-days-conferences/pages/2013-evolution.aspx
- M Verhaegen & S Munro 2011 “Pachyosteosclerosis suggests archaic Homo frequently collected sessile littoral foods” HOMO – J compar hum Biol 62:237-247
- M Vaneechoutte, S Munro & M Verhaegen 2012 “Reply to John Langdon’s review of the eBook: Was Man more aquatic in the past?” HOMO – J compar hum Biol 63:496-503