Question

Why are we not seeing novel life forms arising on Earth continually?

Earth's biosphere is teaming with life in every corner, from large mammals to the smallest of microbes finding their niche in extreme environments. Each has adapted to a particular environment, to which it is ideally suited, and it appears that most, if not all, plausible ecosystems have been exploited by living organisms. Most scientists consider it inevitable that life, similar to the earliest forms, does indeed spontaneously erupt occasionally. It is believed that these tiny populations of organized amino acids and carbon structures, though, would hardly have sufficient time to evolve before some more highly developed organism (though likely still a microbe itself) comes along and processes them as foodstuff. Indeed, the struggle for life today would be infinitely more competitive than it was at the dawn of life. Any life form with less than a cellular organization and lacking a highly specialized and vacant realm in the ecosystem would most certainly meet a hasty demise. Existing life, then, certainly may inhibit the formation of new organisms simply due to the competition of all life for limited resources. It just so happens that the simplest forms of life would also be the easiest to digest and use as energy sources or nutrients, a serious disadvantage for emerging life! In fact, this helps explain why evolutionary theory generally traces back all current earthly life to a common single-celled ancestor. Once this organism had reproduced in sufficient numbers, it would have been able to out-compete any otherwise viable forms emerging later. This most certainly does not mean that a lifeless Earth-like planet could not generate such organisms. The exact opposite is true, since without competition, any emerging life would have a monopoly on the processing of organic nutrients. It is not until one form of life has firmly taken hold of a large-scale ecosystem that other proto-forms are effectively suppressed. For more information on this topic, visit any of the websites listed below: http://origins.jpl.nasa.gov (Site with a wealth of information on the origins of life) www.talkorigins.org (devoted to discussion of biological and physical origins) www.nsf.gov/home/crssprgm/lexen (Life in extreme environments/niches)
May 1, 2002