Practicalities and beyond

Reconstructing all this evolutionary history can have practical implications. Early in Keeling’s career, he investigated the peculiar discovery that malaria parasites have remnants of organelles that once carried chlorophyll. “Why would malaria have a chloroplast? They live in the dark,” Keeling says. The researcher, Iain Wilson, who originally proposed the notion was dismissed for a long time as ridiculously wrong. But evidence grew, and today scientists agree that a certain small bit in the parasite left over from a photosynthetic past still has some function in the dark. That finding helps explain the effectiveness of some formerly mysterious treatments for malaria: The drugs attack chloroplasts.

A realistic tree of life can also change the way researchers look at more theoretical questions, such as how in the world such a supposedly wasteful and irrational process as sex evolved. Only one of two partners can bear young, halving productivity from the start. Or so goes a long-running thread of research and debate (SN: 2/14/09, p. 16).

Yet that furor is so multicellular. Simpson and Roger along with philosopher Maureen O’Malley of the University of Sydney in Biology & Philosophy in 2013 pointed out that the basics of sex must have evolved long before birds, bees or anything else multicellular.

In single-celled organisms, reproduction does not require sex, nor does sex always produce offspring. Two ciliate cells can meet, mingle genes and remain only two cells. The eukaryote tree abounds with single-celled organisms practicing the basics that combine to make multicellular reproduction possible. The alleged wastefulness of sex is really a question of why the peculiar form of sex tied to multicellular reproduction persists in a few outliers.

Useful as a good tree of life can be, Keeling objects to the idea that eukaryotes should be appreciated just for their utility. People enjoy animals and plants for their own sake. “A giraffe won’t save your life, but people like giraffes,” he says. To him, one-celled eukaryotes are Serengeti charismatic, just smaller. Some species have a structure — similar to camera-like animal eyes — with a cornea-like outer covering derived from mitochondria and a light-sensitive inner cup from an engulfed red-algal organelle, Keeling and colleagues reported July 9 in Nature. Several large dinoflagellate species hunt despite living inside a rigid shell. They push a stomachlike structure out a hole in the shell and digest prey larger than they are. Other single cells grow delicate, multipointed outer casings that eventually wash ashore, covering beaches with millions of miniature stars.

Knowing that the living world has so much invisible variety can change a person’s perspective, says Fabien Burki, who works with Keeling at the University of British Columbia. The supergroup tree offers the little back-of-the-neck shiver-thrill of realizing that every tomato patch, termite gut or beach bucket of seawater holds life much vaster and stranger than imagined. Says Burki: “It’s like the astronomers discovering there are planets around other stars.”

Поиск по сайту: