Evo-Devo: Characteristic Beliefs

Evo-Devo: Characteristic Beliefs

1) Internalist model: biochemical foundations limit and may sometimes direct the next steps in morphological and behavioral change.

2) Very old foundations (e.g., serotonin or dopamine) that may go back 2 billion years or more. Modern organisms, plant or animal, have intracellular genetic elements that are very old. Those elements gave a platform for new structures and behavior by duplication, mutation, or forming new links with other genes. (The effect is like using to close programs whether in MS-DOS or in the latest version of Windows, or to cut text by highlighting and or paste it by pressing . Similarly, Compuserve in a Windows format still allows the Unix command "go."

3) A broad array of new body plans (30-35) appeared 540 mya in Cambrian Era, plans that became modern phyla. Only one of them emerged 10 million years later.

4) Much of evolution consists of changing preexisting structures by disinhibition (Hsp-90), inhibition, heterochrony, and using existing structures for new purposes but duplicating the underlying genes. Much of variation between species may consist of mutations that alter appearances or behavior in ways that affect sexual selection more than survival. For example, the bar-headed goose changed one proline to an alanine in its hemoglobin, increasing hemoglobin's affinity for oxygen but without changing its 3D structure. The bar-head can fly over Everest (Gerhart & Kirschner, 1997). Did lots of ganders struggle up that mountain and die before one of them with the correct mutation made it? Or did one of them mutate first, then reach very high and attract the ladies?

5) Bodies of vertebrates and arthropods share a common Hox organization and have similar body plans as embryos. Hox genes...a linear array of 8-13 genes that switch on in linear sequence: body compartments are initiated in the same order that the genes occur. Hox manages both anterior-posterior and dorsal-ventral gradients.

6) Our brainstem, and that of every other creature, is organized under a Hox baton. Our diencephalon and forebrain, however, are initiated by suradded genes that are equivalent to Spiracule and Antennadae, also suradded, in Drosophila.

7) Pax-6 for vision: The poster child of regulatory genes. Take a Pax-6 from a mouse and swap it onto a Drosophila: a fly eye rather than a round brown one emerges wherever (leg, wing, antenna) you inserted Pax-6. Thus, Pax-6 organizes the activity of other genes in the fly, perhaps as many as 2500 of them. (You can use Pax-6 from a squid with the same outcomes.)

8) Duplication of existing genes allows new functions to be taken by the second copy of a gene while continuing the older functions with the first copy. Example: flies have one Hox assembly, lamprey eels have three, mice and men have four. Instead of 6 different Pleistocene variables exploding human intelligence, a gene duplication could have said, "copy 3 times instead of 4." The foundation was created for individuals who saw more complex social opportunities and saw more delayed connections between external events. Natural selection then acted on them (Brody, in press). Duplication also allows greater variation in gene expression because duplication occurs in compartments that integrate with older structures during development. This variation can involve the onset, duration, and termination of gene activity: variation that contributes to heterochrony, changes in the timing of some developmental systems (such as sexual maturation) but not others (brain growth).

9) Both evolution and personal development channeled: ontogeny and phylogeny are similar! (Haeckel was partially correct even though he fudged data!)

10) About Exploratory systems: generate random variation and retain strategies (structures) that achieve a specific outcome. Examples: immune system, microtubules in a cell, stem cells, and our brains. Might include parents as exploratory systems oriented around a child and every organism as an exploratory system oriented to its own interests.
Another example: "Our brains differ as much as our bodies. Indeed, they may differ more. One part of the brain, the anterior commissure ... varies seven-fold in area between one person and the next. Another part, the massa intermedia ..., is not found at all in one in four people. The primary visual cortex can vary three-fold in area. Something called our amygdala (it is responsible for our fears and loves) can vary two-fold in volume --- as can something called our hippocampus (involved in memory). Most surprisingly, our cerebral cortex varies in non-learning impaired people nearly two-fold in volume" (Skoyles & Sagan, 2002)
Another example: "Stomachs vary 8 fold, retinas vary x3 re # cones in fovea, some women have 4 retinal pigments instead of 3, children's sinuses vary x20, temperature has a range of 96-100 F, the ideal value of 98.6F applies to 1 of 12, muscles for index finger may attach to 2nd finger, 1 in 8 people are w/o plantaris longis for wrist flexion, 1 in 100 with 2 plantaris longis, pectoral muscles attach to diff ribs... 2, 3, 4, 5 or 3, 4, 5 or 3, 4, or 2, 3, 4, some of us have 7 fingers" (Skoyles & Sagan, 2002)
A final example: "The structural variability of the brain does not usually affect gross anatomical features that are characteristic for the animal species. But the size and position of cortical areas, the distribution of neurotransmitters, and peptides, the thickness of fiber tracts, the number of neurons constituting a nucleus, the recruitment of muscles during stereotyped behaviors such as locomotion, and particularly the microanatomy of neurons and neuronal circuits vary significantly from individual to individual in virtually all animal species. Structural variability is not genetically coded but represents the result of epigenetic regulatory processes acting during development" (Sporns, 1994).

Notes & Refs:

Gerhart, John & Kirschner, Marc (1997) Cells, Embryos, and Evolution. Malden, MA: Blackwell.
See Judson, O, 2002, Dr. Tatiana's Sex Advice for All Creation for myriad examples of strange adaptations that may have "just happened" and were maintained by their attractions to mates or resistance to predators.
Skoyles, J. and Sagan, D. (2002) Up from Dragons. NY: McGraw Hill, p. 26 and 33. Many nifty observations in a scattered book.
Sporns, O., (1994) Selectionist and instructionist ideas in neurobiology. In O. Sporns & G.Tononi (Eds.) Selectionism and the Brain: International Review of Neurobiology. 37, 4-26. NY: Academic, p. 10.

Copyright 2002, James Brody, all rights reserved.

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