Charles Darwin was arguably the most radical, disruptive thinker of the 19th century, and his theories on evolution provoked as many questions as answers. Many of the mysteries stemming from his ideas were explored this month as part of a three-day MIT conference that celebrated the 200th birthday of the famed naturalist and examined his continuing impact on geology, biology and culture.
Among the questions addressed at the Jan. 22-24 Darwin Bicentennial Symposium were "How did fish start walking on land?" "Why do animals that live in dark underground caves lose eyesight and pigmentation?" and, "If humans evolved from primates, why aren't we continuing to evolve?"
The conference was meant not only to explore the ongoing questions posed by Darwin's work, but also to underscore the important place of evolution in education, said symposium organizer and MIT Professor of Molecular Biology Jonathan King. He explained that the event was partly geared toward high school biology teachers, many of whom struggle to make Darwin and evolution relevant to their students.
"The bicentennial was an opportunity that we didn't want to pass up," King said.
The conference, which took place a few weeks before the Darwin's Feb. 12 birthday, began with an examination of the evolution of the solar system and the Earth and continued with sessions on the mechanics of evolution, Darwin's impact on culture and other topics.
The session on "Evolutionary Mechanisms Among Vertebrates" was perhaps the most significant, King said, as it featured lectures by Farish A. Jenkins Jr., the Alexander Agassiz Professor of Zoology at Harvard University; Cliff Tabin, of the Department of Genetics, Harvard Medical School; and Pardis Sabeti, assistant professor in the Department of Organismic and Evolutionary Biology at Harvard -- all described by King as world leaders in their respective fields.
The session featured a discussion on the evolution of fins into limbs, which King called one of the most important transitions in evolution.
Evolutionists have theorized that land creatures evolved from fish, but proof of such a change --Â fossil evidence of the intermediary physiology of ocean animals that ventured onto land --Â has been hard to come by. That changed when Jenkins' team discovered the remains of an unusual creature that 375 million years ago had the anatomical capabilities to move from shallow water to land.
With great relish, Jenkins described the discovery of a fossil of the long-extinct Tiktaalik roseae, which had weight-bearing fins that could assume both fin-like and limb-like postures. Darwin and others had theorized about such creatures; its remains were finally found in 2006 in the Canadian Arctic.
Another issue that intrigued Darwin and continues to interest researchers today was why dark, underground cave environments worldwide produce fish, insects and other animals that are blind and lack pigment. Losing eyesight or pigment doesn't seem to add any evolutionary advantage so why did this mutation get passed along? Many conclude that some mutations are "neutral" in their effect.
However, Tabin, who has researched the blind Mexican Cave Tetra or Astyanax mexicanus by crossing it with similar, sighted tetras, suggested that the loss of eyesight does reflect natural selection by conferring three possible advantages: eyes are vulnerable to infection, eyes have an "energy cost" to the body and no eyesight provides more neural space for other necessary senses, such as taste.
Darwin's research in the Galápagos Islands included his speculation on why local finches -- now called Darwin's finches -- evolved to have a variety of beaks: short, long and broad. Tabin's team, working with finch embryos, has been able to target the genes that control for beak size and create, for example, broad beaks in normally short-beaked birds. Such work has implications for manipulating what Tabin calls a species' blueprint, to "make a cat instead of a mouse," as he put it.
While anti-evolutionary groups may argue that humans are immune from evolution, Sabeti showed how humans are continuing to evolve. She cited the human ability to digest cow's milk, which developed rapidly over a space of 10,000 years and coincided with the domestication of cattle. Being able to digest a ready protein source and to also wean babies more quickly conferred evolutionary advance.
A version of this article appeared in MIT Tech Talk on February 4, 2009 (download PDF).
