In casual encounters with the material universe, we rarely feel any difficulty here, since we usually deal with things that are clearly alive, such as a dog or a rattlesnake; or with things that are clearly nonalive, such as a brick or a typewriter. Nevertheless, the task of defining "life" is both difficult and subtle; something that at once becomes evident if we stop to think. Consider a caterpillar crawling over a rock.
September 1, ] 1. It also discusses several issues related to speciation. I have divided this FAQ into several sections. Part 2 discusses several definitions of what a species is. Part 3 explains the context in which observations of speciation are made. Part 4 looks at the question, "How can we tell when a speciation event has occurred?
Part 6 is a list of references. The descriptions of each observation come from the primary literature. I went back to this literature for two reasons.
First, many of these observations are not discussed or not discussed in much detail in secondary sources such as reviews, texts and popular articles. Second, it is difficult, if not impossible, to evaluate what a piece of research actually established without looking at the methods and data.
Secondary sources rarely give this information in any detail. Anyway, I have included only those observations that I have been able to find the original sources for.
I consider this FAQ incomplete. One reason for this is that I am still chasing references I still have a list of over to find.
More important is the fact that observations of speciation are buried in papers on a number of topics.
If you know of observations that I should include, let me know and I will chase down the reference, read it and modify the file assuming that the data are the least bit convincing.
I ask that you try to give me as complete a reference as possible to aid me in finding the original source.
These questions got me interested in the topic. I hope that I have, at least, provided grist for the mill that will grind out an answer to Rich's questions.
In any case, Rich deserves the credit or blame: My starting point was the references contained in the old speciation FAQ. Tom Scharle and Simon Clippingdale sent a couple of references my way. Finally, John Edstrom sent me considerable information on symbiosis in Amoeba.
While I have not had a chance to get all the references that he has sent me, he has given me a great deal to think about over the role of symbiosis in speciation. Many thanks to all. This is a topic of considerable debate within the biological community. Three recent reviews in the Journal of Phycology give some idea of the scope of the debate CastenholzManhart and McCourtWood and Leatham There are a variety of different species concept currently in use by biologists.
These include folk, biological, morphological, genetic, paleontological, evolutionary, phylogenetic and biosystematic definitions.
In the interest of brevity, I'll only discuss four of these -- folk, biological, morphological and phylogenetic. A good review of species definitions is given in Stuessy In societies that are close to nature, each taxon is given a name.
These sorts of folk taxonomies have two features in common. One aspect is the idea of reproductive compatability and continuity within a species. Dogs beget dogs, they never beget cats! This has a firm grounding in folk knowledge.
The second notion is that there is a discontinuity of variation between species. In other words, you can tell species apart by looking at them Cronquist This concept defines a species as a reproductive community. The earliest precursor that I could find was in Du Rietz Du Rietz defined a species as " A few years later, Dobzhansky defined a species as " It emphasizes experimental approaches and ignores what goes on in nature.
By the publication of the third edition of the book this appeared in, Dobzhansky had relaxed this definition to the point that is substantially agreed with Mayr's.A Definition of Life.
The ubiquity of life In earlier chapters we considered the astronomical environment which extraterrestrial lifeforms must cope with. Other galaxies, stars, and countless planets appear amenable, if not perfectly hospitable, to life.
Devil In The Dark () The Horta was an example of Silicon life.; Now we are really sailing off into terra incognito. "Here be dragons" and all that. But if you have starships, you almost have to have aliens (Isaac Asimov's Foundation trilogy being the most notable exception).The "science" is called Astrobiology, the famous "science in search of a subject".
A look at a large number of observed speciation events. Not only does this article examine in detail a number of speciation events, but it also presents a brief history of the topic of speciation.
is and in to a was not you i of it the be he his but for are this that by on at they with which she or from had we will have an what been one if would who has her. During meiosis.
It was the behaviour of chromosomes during meiosis, however, that provided the strongest evidence for their being the carriers of genes. Evolution - The science of evolution: The central argument of Darwin’s theory of evolution starts with the existence of hereditary variation.
Experience with animal and plant breeding had demonstrated to Darwin that variations can be developed that are “useful to man.” So, he reasoned, variations must occur in nature that are favourable or useful in some way to the organism itself in the.