Chapter 116 19.5 Strange has its way

The difference between wild evolution in nature and synthetic evolution on a computer is this: software has no body.You use a floppy disk to load the program onto the computer and it is a straightforward process.If you change the program code (hoping for better results), just run it and see the result.There is nothing superfluous between what the code is and what it does, just the computer hardware that runs the code. Biology is very different.If we treat a hypothetical piece of DNA as software code and make a change to it, an organic entity must develop accordingly before the result of the change can prove itself.It may take many years for an animal to develop from a fertilized egg to an egg-layer.Therefore, the effect of the modification of the biological code can be judged differently according to the different developmental stages.The same changes made to the code in the first place would have one effect on the growing tiny embryo and another effect on the sexually mature organism (if the embryo survived to that point).At every stage of an organism, between changes in the code and its end effects (eg, longer fingers), there are a series of intermediate entities controlled by physical or chemical changes—enzymes, proteins, and living tissues—that also It is bound to be indirectly affected by code changes.This greatly increases the complexity of the mutation.Computers that run programs are no match.

You were once the size of a period.Before long, you're a rolling multicellular ball—much like algae in a pond.The current washes over you powerfully.do you remember?Then you grow up.You become a sponge, a coelenterate, with only one rectum in your body.Eating is the content of your life.You gradually grow the spinal nerves that sense the outside world; slowly add the jaws for breathing and chewing.You grow a tail again for swimming and turning.You are not a fish, but a human embryo playing the role of a fish embryo.You sneak in and out of the ghosts of each animal embryo, replaying the possible roles you had to give up to get to the finish line.Evolution is the submission to selection.To grow into a new species is to go through all the roles you no longer play.

Evolution is creative and conservative, always making do with what's already there.Creatures rarely start from scratch.The past is its starting point, and the essence of the past is condensed in the development of the organism.When an organism begins its development, the millions of compromises it makes block its way to evolve in other directions.Evolution without a body is unlimited evolution.However, the evolution of entities is restricted by many conditions, and the existing success prevents it from going backwards.But these constraints also give evolution a place to stand.If artificial evolution really wants to achieve something, it may also need to be attached to a body.

Time begins to tick as the body takes shape.Along the dimension of time, the flower of mutation blooms in a growing body. (This is another thing that artificial evolution has so far had little to offer: the timing of development).To alter the early development of an embryo would be a disrespect to time.The earlier a mutation occurs during embryonic development, the more drastic its impact on an organism.It also weakens the constraints against failure.Therefore, mutations that come earlier in development are less likely to succeed.In other words, the more complex the organism, the less likely it is that early mutations will occur.

Mutations in early development often affect the whole body.A well-placed change can spark or undo the fruits of millions of years of evolution.The famous antennal foot mutation in Drosophila is an example.This single-point mutation messed up the limb-forming system of the fruit fly embryo, producing a leg where an antennae should have been.Distressed fruit flies are born with a prosthetic limb protruding from their foreheads—a tiny change in the genetic code that triggers a cascade of other genes.Any kind of monster can be hatched by this method.This has aroused the curiosity of developmental biologists: whether self-regulating genes in organisms can purposely make some changes to genes to create useful monsters, so as to bypass Darwin's gradual Natural selection?

Strangely, though, it seems that these monsters follow some kind of inner law.A two-headed calf may appear to us to be some random defect, but it is not.When biologists study these specific traits, they find that the same type of deformity occurs in many species, and the specific traits can be classified.Cyclopsia, for example—a relatively common anomaly in mammals, including humans who are born with one eye; and animals with this anomaly, regardless of species, almost always have nostrils in their eyes above.Similarly, doubles are usually more common than triples.Whether it is double-headed or triple-headed, it is a variation without any advantages.Since few of these monsters survived, it was impossible for natural selection to have any preference between the two.Then this mutated instruction must come from inside.

In the early and mid-nineteenth century, a French father-son duo—Father Saint-Tirrell and son Saint-Tirrell the Younger—designed a system of classification for these monsters of nature.This system of classification corresponds to the Linnaean system of classification of species: each aberration is assigned a class, order, family, genus, or even species.Their work laid the foundation for the modern science of teratology, the study of monsters.The St. Tyrrells imply that ordered forms are broader than natural selection. Pierre Abbotcher of the Harvard Museum of Comparative Zoology is a contemporary advocate for the importance of teratology in evolutionary biology.He sees teratology as an overlooked blueprint for robust intrinsic self-organization processes in living organisms.He asserts that "teratology provides a detailed account of the possibilities underlying a developmental process. Teratology not only occurs in an organized and discrete occur, and exhibit universal laws of deformation. These properties are not confined to the realm of teratology; rather, they are universal properties of all sustainable systems."

The orderly interiors of monsters—such as the fully developed legs emerging from the foreheads of mutant fruit flies—reveal a deeply lurking inner force that influences the organism's external shape.This "internalism" is completely different from the orthodox "externalism" held by most adaptation theorists.The latter argue that pervasive selection is the main force shaping the shape of organisms.And as a dissenting immanentist, Abbotcher writes: Internalism is based on such an important assumption: the diversity of morphology is caused by the perturbation of various parameter values ​​(such as diffusivity, cell adhesion, etc.), and at the same time, the interaction relationship between the various components of living organisms The structure remains constant.Under this premise, even if the values ​​of the system's parameters are randomly perturbed during development—either by genetic mutation, or by environmental change or human manipulation—the system will only produce a certain finite, discrete subset of phenotypes .That is, the set of possible forms is a representation of the internal structure of the system.

Thus, the two-headed monsters we see may have arisen for the same reason that we have symmetrically growing arms; it is likely that neither is due to natural selection.On the contrary, the internal structure, especially the internal structure of chromosomes, and the accumulated morphological changes during development play a role equal to or beyond natural selection, resulting in the diversity of biological tissues.