Dear Phil:
OK, here I am finally responding to you after 12 days, during half of which I did not even know you had responded (it got temporarily buried, I'm afraid). I'll do my best to do better in the future, if there is one.
A species is, technically, a genetically very closely similar population of organisms that are capable of reproduction. Some species are more variable than others and may thus be subclassified into subspecies. Going up the taxonomic ladder, a group of similar species constitutes a genus, similar genera constitute an order, then a class, a division. and a kingdom (or phylum), I believe. But the key to a species, apart from the close physical similarity of individuals, is the ability of the members of a population to freely interbreed. When the number of individuals in the population declines below some threshold (which varies for each species), the population typically becomes extinct as the remaining individuals age and die or are killed.
I do not know the number of species and doubt that anyone does. Certainly it is in the millions. Insects have by far the largest number of species, and undoubtedly dozens do become extinct every day because many are very concentrated in their geographic distribution. So if 27,000 species became extinct in a given year, some large percentage of those would be insects. And the vast number of those extinctions probably occur in biologically disturbed areas of species-rich zones like the tropics, not Seattle. So you personally would not observe this process occurring in an overt way. Nevertheless, these extinctions of insects in the tropics are biologically significant because they permanently deplete the gene pool of the earth and may affect, e.g., animals that feed on them.
Once a species is gone, it's gone forever (unless genetic engineering can resurrect it, which is currently becoming possible, although who knows where we will find the room for herds of mastodons). New species may evolve, but the time scale of evolution is too slow for us to perceive and really has no relevance to human experience.
The relationship between population growth and extinctions is direct in a global sense but far more variable on a local scale. In an area like Seattle you would be unlikely to witness many extinctions, but rather a progressive intrusion of human activities into natural areas (primarily through construction activities, which basically replace nature with artificial and depauperate environments). In a country like Cameroon extinctions from insects to mammals are frequent.
Best wishes and hope to hear from you soon,
Steve
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Dear Steve,
Thanks for your email and for taking the time to answer my questions about species. I am currently down in Peru visiting a Center I helped found about eight years ago.
I do have more questions, but still am wondering whether dogs are all one species. Also whether 99+% of all species are now exctint.
My question about whether humans have observed the emergence of a new species comes partly from reading Stephen Jay Gould where he gives the impression that instead of species branching out what we actually have is a funneling down process. Would appreciate your comments.
Sincerely,
Fr. Phil Bloom