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Several developments underlie this trend. Biologists have come to recognize the many ways in which evolution has forged commonalities among organisms.
"There are much greater similarities at the genetic level than biologists had appreciated, profound similarities," says Carroll. "That forced a rethinking. It meant that a generation of biologists had to learn not only about the connections among organisms but also about how those connections could be used as research tools."
New genomics data have highlighted these evolutionary links. Whereas biologists used to rely on similarities in shape or behavior to draw evolutionary connections, they now can reconstruct evolutionary lineages by analyzing DNA sequences. "You can document the dramatic genetic events that changed the nature of an organism over evolutionary time," says HHMI investigator David Haussler at the University of California, Santa Cruz.
Biologists increasingly have realized that questions involving evolution have important connections to other scientific fields.
In addition, biologists increasingly have realized that questions involving evolution have important connections to other scientific fields. And as they have forged multi-disciplinary collaborations with chemists, geologists, computer scientists, and social scientists, new ideas and techniques have flooded into the biological sciences.
The growing prominence of evolutionary biology is apparent in the work of many HHMI investigators. Here are five examples.
In principle, evolution is remarkably simple. Among assemblages of molecules able to reproduce themselves, some copies turn out slightly different from the original. When a variant appears that is better able to survive and reproduce, it will become more numerous. And as these entities continue to copy themselves and change, some will come to exploit existing resources in new ways or move into new environments.
Biologists may never know exactly which molecules came together to form the first living organisms, but HHMI investigator Jack W. Szostak, a geneticist at Massachusetts General Hospital and Harvard Medical School, is very close to demonstrating how the process could have occurred early in Earth's history. In his laboratory at Massachusetts General Hospital, Szostak and colleagues synthesized chains of nucleic acids that can latch onto other nucleic acid chains (including copies of themselves) and partially copy those chains. On the early Earth, reproducing chains of nucleic acids could have formed within vesicles composed of fatty acids, which could have been plentiful in certain places. This compartmentalization is critical, Szostak points out, because otherwise, highly efficient replicators will make copies of all the nucleic acid chains around them. If they are isolated inside a vesicle, however, they will make more copies of themselves and thereby increase in number.
A major challenge for Szostak's team has been devising a way of coordinating the growth and division of the vesicle with the replication of its contents. After examining several possible mechanisms, "we worked out an idea that was relatively simple," he says. They found that putting nucleic acid chains inside a vesicle creates osmotic pressure inside the membrane. These highly pressurized vesicles are able to absorb fatty acids from less-pressurized vesicles and grow. If these growing cells divide randomly or at a certain size threshold, they reproduce faster than less rapidly growing cells. In this way, says Szostak, a highly efficient nucleic acid replicator could outcompete less efficient replicators.
The outcome is natural selection among membrane-encapsulated nucleic acid chains. "It's a nice simplification of the whole process," says Szostak. Different replicator-vesicle packages compete with each other to become more numerous, so Darwinian evolution can occur with relatively simple molecular systems. Once these simple cells start competing, Szostak believes, there is a "snowball effect. You start to get additional functions evolving, and that's going to lead to changes in the membrane composition. The whole system is going to be under pressure to get a lot more complicated pretty quickly."