21/3/2022: Development in Evolutionary Thought: Introduction
Development: change in morphology and structure of organism from fertilization to adult
All cells in the body are copies of the mother → going all the way back in time → all cells are
copies of the first living cell.
Mushroom example → spots are not genetic → protect the mushroom in the early stages → as
the mushroom grows, it is spread out across the surface → other mushrooms have the same
protection, but instead of spreading over the surface, the protection remains underground →
therefore gene is not necessary for spots → gene might influence how well it stretches or
brakes → developmental explanation more fitting.
Aristotelian ideas: development was the original way of explaining ecology, but was not used
anymore after Mendelian genetics were found. During the 20th century, a change back to
Aristotelian ideas happened.
Aristotelian ideas have 5 fundamental ideas that are fundamental to biology:
- A desire to explain features of animals with reference to their function (=adaptation)
- The teleological argument, lacking evolutionary theory (since during this time evolution
was not a concept)
- Recognition of homologous structures (windpipes in different air-breathing species)
- Recognition that animals function as a coordinated set of traits (if you have blood, you
need a heart; if you breathe air, you don’t have gills)
- Categorization of animals according to the general adaptations → posits a bunch of
traits that define different “types” of animals (eg. animals with blood, live-bearing animals
vs. egg-laying animals,).
+ Examples of the Aristotelian ideas
Spontaneous generation: before the 17th century, it was commonly accepted that life grows
out of other types of life or non-life (for example: meat makes maggots, trees make birds).
Preformationism: the structures that make up the body are all present from fertilization and
simply grow and change their shape and organization during development. This position is often
unfairly caricatured.
Recapitulation: during development and growth (ontogeny) from fertilization to adulthood the
animal passes through embryonic stages that reflect the adult form of the animal’s distant
ancestors (phylogeny) → stated as the biogenetic law → ontogeny recapitulates phylogeny.
, Biogenetics has 3 laws:
- Law of correspondence: each stage of development in higher animals corresponds to
the adult stages of lower animals
- Phylogenesis: occurs by adding new stages to the end of normal development
- Truncation: continual addition of new stages at the end of development will result in
development taking too long. So, the earlier stages will speed up while the new stages
will be slower
Fertilized egg → Fish → amphibian → human. This idea of recapitulation introduces an
important concept: differences in adult animal form result from changes in developmental timing:
heterochrony
Von Baer’s principles → outlines a set of developmental principles:
1. More general characters of a large group appear earlier in the embryo than more special
characters → rejection of preformatism
2. From the most general forms, the less general form is developed, and so on until finally
the most special arises → the idea of specialization → all have paws, but some have
claws → specialization of the paws.
3. Every embryo of a given animal form, instead of passing through the other forms, rather
becomes separated from them → rejection of recapitulation
4. Fundamentally, therefore, the embryo of a higher form never resembles any other form,
but only its embryo → rejection of recapitulation
All animals share the first stage of embryonic development. Fish and mammals have the first 3
stages in common. During development, different types of animals diverge, they do not
recapitulate.
Concepts of heredity → Lamarck's idea → animals inherit traits due to the need for this trait →
main example: the giraffe's neck → this is not explaining how information about the need for a
long neck is passed on to offspring.
Concepts of heredity:
Functional: traits are explained with reference to their
functional needs and conditions of existence → are talking
about the accumulation of small changes over time
Structuralist: traits of animals are best explained as
variations on a single underlying form → are talking about
the structure of the whole body
Development: change in morphology and structure of organism from fertilization to adult
All cells in the body are copies of the mother → going all the way back in time → all cells are
copies of the first living cell.
Mushroom example → spots are not genetic → protect the mushroom in the early stages → as
the mushroom grows, it is spread out across the surface → other mushrooms have the same
protection, but instead of spreading over the surface, the protection remains underground →
therefore gene is not necessary for spots → gene might influence how well it stretches or
brakes → developmental explanation more fitting.
Aristotelian ideas: development was the original way of explaining ecology, but was not used
anymore after Mendelian genetics were found. During the 20th century, a change back to
Aristotelian ideas happened.
Aristotelian ideas have 5 fundamental ideas that are fundamental to biology:
- A desire to explain features of animals with reference to their function (=adaptation)
- The teleological argument, lacking evolutionary theory (since during this time evolution
was not a concept)
- Recognition of homologous structures (windpipes in different air-breathing species)
- Recognition that animals function as a coordinated set of traits (if you have blood, you
need a heart; if you breathe air, you don’t have gills)
- Categorization of animals according to the general adaptations → posits a bunch of
traits that define different “types” of animals (eg. animals with blood, live-bearing animals
vs. egg-laying animals,).
+ Examples of the Aristotelian ideas
Spontaneous generation: before the 17th century, it was commonly accepted that life grows
out of other types of life or non-life (for example: meat makes maggots, trees make birds).
Preformationism: the structures that make up the body are all present from fertilization and
simply grow and change their shape and organization during development. This position is often
unfairly caricatured.
Recapitulation: during development and growth (ontogeny) from fertilization to adulthood the
animal passes through embryonic stages that reflect the adult form of the animal’s distant
ancestors (phylogeny) → stated as the biogenetic law → ontogeny recapitulates phylogeny.
, Biogenetics has 3 laws:
- Law of correspondence: each stage of development in higher animals corresponds to
the adult stages of lower animals
- Phylogenesis: occurs by adding new stages to the end of normal development
- Truncation: continual addition of new stages at the end of development will result in
development taking too long. So, the earlier stages will speed up while the new stages
will be slower
Fertilized egg → Fish → amphibian → human. This idea of recapitulation introduces an
important concept: differences in adult animal form result from changes in developmental timing:
heterochrony
Von Baer’s principles → outlines a set of developmental principles:
1. More general characters of a large group appear earlier in the embryo than more special
characters → rejection of preformatism
2. From the most general forms, the less general form is developed, and so on until finally
the most special arises → the idea of specialization → all have paws, but some have
claws → specialization of the paws.
3. Every embryo of a given animal form, instead of passing through the other forms, rather
becomes separated from them → rejection of recapitulation
4. Fundamentally, therefore, the embryo of a higher form never resembles any other form,
but only its embryo → rejection of recapitulation
All animals share the first stage of embryonic development. Fish and mammals have the first 3
stages in common. During development, different types of animals diverge, they do not
recapitulate.
Concepts of heredity → Lamarck's idea → animals inherit traits due to the need for this trait →
main example: the giraffe's neck → this is not explaining how information about the need for a
long neck is passed on to offspring.
Concepts of heredity:
Functional: traits are explained with reference to their
functional needs and conditions of existence → are talking
about the accumulation of small changes over time
Structuralist: traits of animals are best explained as
variations on a single underlying form → are talking about
the structure of the whole body
