Embryology Test 4: Beginning of Life

Organism creation

-Entity undergoes biological change
-Entity becomes a new substance (a new organism)

Development (different from organism creation)

-Organism undergoes biological change
-same entity before and after - same organism before and after
-start of development = beginning of life

Carnegie stages

developmental stages in vertebrates
-starts at fertilization
Categorized by visible structures
-not days or size
-applicable to different developmental rates and wide variety of species
only covers embryonic development
- does not cover fetal development

What is the general current scientific opinion on when human life begins?

At fertilization

Can chromosomal constitution define a human organism? And why?

No, not sufficiently
-DNA mutations can alter genetic code of individual cells without creating an organism
-Altering an adult's DNA doesn't make them a new person

Can chromosomal constitution define a human organism?

No - ex. identical twins have same genetic code without being the same organism

What are 4 biological categories to explain?

1. Standard cases
2. unusual cases
3. Non-organismal cases
4. Controversial cases

Standard cases

cases of common and typical development

2 types of standard cases

1. Normal development
2. Multiple species

Standard cases: normal development

When in the process of fertilization does life begin?

Standard cases: Multiple species

A good definition should be applicable across multiple species
-Implantation-based criteria don't apply to organisms without a womb
-Birth-based definitions don't apply to organisms that aren't born

Two types of unusual cases

1. Developmental anomalies
2. Identical DNA offspring

Unusual cases: developmental anomalies

-can result in odd DNA contents
-Criteria based on a certain amount of DNA can't explain these cases
-Loss of a structure:criteria based on existence of thinking part of brain (cerebrum) can't explain surviving anencephalic infants

Identical DNA offspring

Many organisms can create clones with identical DNA to parent
-causes problems for criteria based on new DNA content

Non-organismal cases

entities that have commonalities with organisms, but are not themselves organisms
examples: biofilms and cities

Controversial cases

cases where the metaphysics are uncertain and/pr debated
-a good criteria should be able to explain these
Ex. monozygotic twinning

4 ways to explain twining and the beginning of life

1. non-human twinning
2. Deadly twinning
3. Conjoined twinning
4. Regulative twinning

Non-human twinning

-No organism exists before twinning
-Two organisms exist after twinning
-Probably the most common philosophical opinion

Deadly twinning

-One organism exists before twinning and dies
-Two different twin organisms exist after twinning
-Widely believed by philosophers

Conjoined twinning

-Two organisms created at fertilization
-Twinning separates bodies of both organisms
-Believed by small minority of philosophers

Regulative twinning

-One organism exists before twinning
-A new organism buds off of the first organism
-Assumed to be the case in biology textbooks

Three key questions to discovering a new organism

1. Is there an organism before the event?
2. Is there an organism after the event?
3. If the answer to both of these is yes... is the organism after the same as the one before?