AboutDana Krempels, Ph.D. Expertise I can answer biology-related questions in the areas of evolution, zoology, botany, genetics, and ecology. But I don't answer homework questions or provide ideas for your science fair projects. So students please do your learning the right way by reading your text assignments and studying!
Experience At the University of Miami, I teach Evolution and Biodiversity, Botany, Zoology, Genetics, Ecology, and a variety of seminars (e.g., the Biology and Evolution of Human Gender Roles).
Education/Credentials I have a B.S. in Biology and an A.B. in English from the University of Southern California (1980).
I earned my Ph.D. in Biology in the area of evolutionary biology/visual physiology from the University of Miami in 1989.
Past/Present Clients I am currently an "expert" in both the "Rabbits" and "Wild Animals" categories.
Your very prompt reply seemed to say that there was no scientific answer to my apparently simple question of when species classification applies to any creature, or that perhaps only adult/definitive specimens need apply for membership in their species. I find that rather difficult to understand.
Further, you seemed to say that the proper definition of "organism" was so restrictive as to exclude zygotes of any species, and yet they do survive in the proper environment, which is all that can be said of any organism, is it not?
And finally your say "But if it is not yet viable outside the egg, is it a chicken, or just a potential chicken?" My question to you is: what principle of taxonomy makes "viability" a mandatory property for classification?
ANSWER: Dear Doyle,
I'll bracket your quotes so that I can answer each section in turn:
[Your very prompt reply seemed to say that there was no scientific answer to my apparently simple question of when species classification applies to any creature]
That is correct. The scientific method is used to answer questions by posing a testable hypothesis, and then designing an experiment to challenge that hypothesis with rigor.
If you are able to come up with a testable hypothesis to address when "life" begins, or when a zygote or embryo officially becomes a member of its species, then I would be happy to see and critique it.
But I suspect you will not be able to do it, because you are talking about *definitions*, not about answering a scientific question. The two are very different.
[or that perhaps only adult/definitive specimens need apply for membership in their species.]
Neither zygotes nor embryos nor juveniles nor adults apply for membership to their respective species. They are assigned species status by means of a simple classification method that is (usually, but not always) based upon the characteristics of the fully developed organism or its free-living larval form. The zygote of a particular species is called a "zygote of species XXX".
[I find that rather difficult to understand.]
I hope I have made it a bit more clear for you.
[Further, you seemed to say that the proper definition of "organism" was so restrictive as to exclude zygotes of any species, and yet they do survive in the proper environment, which is all that can be said of any organism, is it not?]
In simple answer to the above question: an organism is defined by more than its ability to survive in the proper environment. A zygote is a zygote. A multicellular life form is just that. What you want to name them is up to you. But a zygote is not an organism. It is a single, fertilized cell that can survive only if it is able to grow and differentiate into whatever finished "product" is encoded by its DNA. That's a simple definition, and I did not devise it.
As a side note: In the future, if you quote me, please provide the direct quote to which you are referring. Do not say that I "seemed to say" something, because that already introduces any bias you might have had in interpreting what I actually did say.
[what principle of taxonomy makes "viability" a mandatory property for classification?]
How about the biological definition of a species:
"A group of similar organisms that can mate with each other to produce fertile, viable offspring."
I did not make up that definition, either. You can find it in just about any good biology textbook.
Hope that helps.
Dana
---------- FOLLOW-UP ----------
QUESTION: Dear Dr. Krempels,
I'll bracket your quotes so that I can ask about each section in turn:
[If you are able to come up with a testable hypothesis to address when "life" begins, or when a zygote or embryo officially becomes a member of its species, then I would be happy to see and critique it.]
"Life" is a continuum, is it not? Therefore the proper question, it seems to me, is when does each new creature begin it's existence as an organism distinct from it's parents. Would you agree? And it seems to me that there is no other time during the existence of any creature that can be singled out other than fertilization.
[The zygote of a particular species is called a "zygote of species XXX".]
Yes of course. Is it not also equally true than an adult of species XXX is similarly referred to as "an adult of species XXX"?
[But a zygote is not an organism. It is a single, fertilized cell that can survive only if it is able to grow and differentiate into whatever finished "product" is encoded by its DNA. That's a simple definition, and I did not devise it.]
Here is a simple definition from Merriam Webster which is slightly different from yours:
Main Entry: or·gan·ism Pronunciation: 'or-g&-"ni-z&m Function: noun Date: circa 17741 : a complex structure of interdependent and subordinate elements whose relations and properties are largely determined by their function in the whole 2 : an individual constituted to carry on the activities of life by means of organs separate in function but mutually dependent : a living being
In what way does a zygote or early embryo not fit that description?
[How about the biological definition of a species:
"A group of similar organisms that can mate with each other to produce fertile, viable offspring."]
Do I understand you to be saying that before any creature may be properly classified as to it's species it MUST BE ABLE TO PRODUCE OFFSPRING AT THAT MOMENT?
ANSWER: Dear Doyle,
["Life" is a continuum, is it not?]
"Life" has a precise, specific definition in the biological sciences, and it is not defined on a continuum. If you wish to see it that way, then you have that prerogative. But it is your own definition, and not one consistent with the definition generally used in the biological sciences.
But the fact that you did not respond to my suggestion that you devise a testable hypothesis and experiment to determine when life begins suggests that you agree with me: this question is in the realm of philosophy, not science.
[Therefore the proper question, it seems to me, is when does each new creature begin it's existence as an organism distinct from it's parents. Would you agree?]
Whether I agree or disagree is irrelevant. The question does not have a single valid answer.
And while this question may be very important to some people--and I respect that--my personal feeling is that the question of when life begins is irrelevant, and does not have a single answer satisfactory to everyone. There is certainly no answer that can be rationally, dispassionately devised. So I will leave the question to those who wish to argue it. I am not among them.
[And it seems to me that there is no other time during the existence of any creature that can be singled out other than fertilization.]
You are certainly entitled to that subjective opinion. But others are just as entitled to subjective opinions that differ from your own.
[Is it not also equally true than an adult of species XXX is similarly referred to as "an adult of species XXX"?]
It can be referred to in this way, but generally this is not done in scientific work. It is understood, unless otherwise noted.
[2 : an individual constituted to carry on the activities of life by means of organs separate in function but mutually dependent : a living being
In what way does a zygote or early embryo not fit that description?]
A zygote does not fit the second description above. It might fit the first, but that one is a very general, inclusive definition.
Even if you wish to consider a zygote to be an organism, then so what? What is your point?
[Do I understand you to be saying that before any creature may be properly classified as to it's species it MUST BE ABLE TO PRODUCE OFFSPRING AT THAT MOMENT?]
That is not what the definition says. I am giving you the biological definition of a species, and you can do with it what you will.
But if you are trying to coerce me into a religious debate about when human life begins, then please stop here. You are wasting your time and my time. The question is NOT scientifically addressable, and so--as I've said several times before--it must remain in the realm of philosophy. And that means that subjectivity will reign. I'm not even going to go there.
Dana
---------- FOLLOW-UP ----------
QUESTION: Dear Dr. Krempels,
["Life" has a precise, specific definition in the biological sciences, and it is not defined on a continuum.}
My apologies for not making myself clear. I used the term "continuum" not as a definition of the word life, but rather to indicate that life itself does not stop and start again, at least in our age. For that reason, the question of when life "begins" seems improper to me, since it never actually ends. And since living sperm and living egg combine to form a living creature with a new DNA code, it seems to me that action marks the beginning of the existence of a new organism. That's what I meant.
[A zygote does not fit the second description above. It might fit the first, but that one is a very general, inclusive definition.]
How many definitions does it need to fit to qualify? Is one sufficient?
[Even if you wish to consider a zygote to be an organism, then so what? What is your point?]
That a new organism has been created, that's all.
[But if you are trying to coerce me into a religious debate about when human life begins, then please stop here.]
Absolutely not. I'm not religious, and I don't believe that life "begins". However, I do believe that we have our humble beginnings as organisms of the species Homo sapiens, at fertilization. Is there any scientific reason to believe otherwise?
Answer Dear Doyle,
[And since living sperm and living egg combine to form a living creature with a new DNA code, it seems to me that action marks the beginning of the existence of a new organism. That's what I meant.]
This is not an unreasonable definition, and many would agree with you. Others might have a different definition, because--like many things in biology--some things defy our ability to easily classify or categorize them.
[How many definitions does it need to fit to qualify? Is one sufficient?]
I imagine so.
[I do believe that we have our humble beginnings as organisms of the species Homo sapiens, at fertilization. Is there any scientific reason to believe otherwise?]
There is no scientific reason to "believe" either way. I have no problem with your defining the beginning of an organism at fertilization, but it is a definition, not science, per se. That's all I'm saying.
