| Some years ago, Margulis promoted a new concept in evolution. Complex life developed from the merging of microbial forms of life. Elements of the cell such as mitochondria, chloroplasts and other organelles came from small, simple lifeforms invading larger cells. The idea was a long time in gaining acceptance, but is now part of conventional evolutionary texts. In this book, she expands her earlier work with some accounts of her life as a scientist and wife of Carl Sagan. She also goes beyond her earlier work to advance a new thesis on the accelerator of evolution - sex. While many of her ideas are presented in more detail elsewhere, this book is a good, quick introduction to fuller accounts of her thinking. Margulis is an innovator - forceful in imparting her ideas. She portrays herself as a rebel from early in her career, arguing here that she was sceptical of "genes in the nucleus determin[ing] all the characteristics of plants and animals." Her misgivings received scant support, however, without a replacement thesis. She found one in symbiosis - the association of multiple organisms. It took many years of investigation, including initial rejection of her attempts to publish, before the idea of SET [Serial Endoymbiosis Theory] found acceptance. So much attention had been focussed the DNA in the cell nucleus that organelle structure and function had been essentially overlooked as irrelevant. That these organelles might have been independent organisms at some point was too novel. Her account of the struggle to gain recognition is related as one of dogged persistence, nearly devoid of outside support . Moving through an interesting discussion of life's origins, she dismisses the notion that forms of nucleic acids arose before simple cells. She finds the natural occurence of lipids [fats] as the more likely precursors of complex life, with RNA and DNA arising as a way to give these fat globules more survival ability. As with her earlier thesis, this one will generate controversy, something Margulis seems nutured on. Her proposal about the emergence of sex will come as a surprise to most readers. In a word, she suggests sex resulting from cannibalism. In Margulis' view, certain microbes under stress, notably the absence of food, turned on each other for survival. The cannibalism was not always fully consummated, she suggests, but the beginnings of mixing genetic material was begun in the process. Incomplete cannibalism could lead to the formation of a new, more complex organism. If this process occurred often enough within a compatible group, the new organism, obviously larger than its predecessors, would be more fit to compete. In conclusion, Margulis makes a strong case in favour of James Lovelock's Gaia concept. This might have been a non-sequitor in the hands of someone less able to deal with novel ideas. Margulis stresses that Gaia has been mistakenly viewed as Earth's biosphere acting as a single organism. She argues that Gaia really means a global network - a "system of organisms." The Gaia concept means the elements of the "system" are tightly entangled and extinctions weaken the structure. If the extinction rate exceeds the rate of recovery the system is endangered. It's interesting to note in light of her definition that the Gaia website still refers to it as a "superorganism," not a "system of organisms." This disparity doesn't detract from Margulis' presentation, which is admirably presented. She offers enough graphic support for the text to clarify or enhance her themes. In all, this is a fine mind-opener in thinking about the development of early life. Readable by anyone interested in life's history and processes. |
home
