Gene Shortage and Evolutionary Psychology
by Dr Beetle
Gene shortage has been used to dismiss the claims of evolutionary psychology, where so much human behaviour is said to be genetically determined. It can take some 100 to 2500 genes to make or work each adaptation, yet the human genome project revealed that there are only some 30,000 functional genes in humans. This is no where near enough to produce all of the behavioural traits being claimed, such as the emotions, fears, disgusts, and daily decisions on levels of promiscuity, helpfulness and conduct. The problem of gene shortage has been championed by Paul Ehrlich. However, evolutionary psychology has returned with its counterclaim, that there is no gene shortage.
Their argument is that if gene shortage is such a problem, then how can there be so many hundreds of adaptations and features in a body. There are already so many types and locations of bone, hair, sense organ, nerves, hormones, blood vessels etc. If there is no apparent gene shortage for making such variety in a body, then why should there be a problem in making a multitude of mind modules and inherited instincts as well? If each gene can work in different combination with other genes, then there are 10 to the power of 86 possibilities that they could control – more than the number of particles in the universe!
However, there is a limit to how many combinations genes can make before nothing is determined or a mess created. It would be a bit like going to committee, and getting no decision. Genes do need to act within set groups and in quite precise sequences. If even one gene is omitted, or a different sequence followed, strange anomalies can occur. For example, incorrect activation of the Antennapedia gene in the Drosophila fly can make a leg grow on its head rather than its antenna. The incorrect mixture of genes in humans can result in genetic diseases such as Down’s Syndrome and Cystic fibrosis. It is actually quite a difficult accomplishment to find the precise set of genes needed to produce something functional like bone or muscle. Even a fraction of the number of combinations thought possible by evolutionary psychology is not possible. Genes cannot chop and change, but have to work together in a very limited number of ways, to avoid making mistakes and mismatches.
Genes lack the numbers to control numerous tasks, and even if they could do more, biologically it would be folly to exclude guidance from a reliable environment. There are many kinds of organs and anatomical details within a body, but these are made from essentially a rather limited set of tissues. Genes concentrate on producing bone, muscle, nerves, collagen etc, and organs are the various combinations of these tissues. But genes do not micromanage when placing a leg or blood vessel in its certain place. They can just as reliably leave a fair chunk of those tasks to the environment of the developing body. Feedback and double checking with the environment is a far more reliable and repairable mechanism than genes trying to insist on control for all structural development themselves.
To see through the scenario of gene micromanagement, think of stem cells. Stem cells are undifferentiated primal or embryonic-like cells that under certain conditions can differentiate into any of the full array of cell types that occur in a body. The decision on what the stem cell will turn into is made by the environment in which the stem cell is placed, not the gene. That is why stem cells are so exciting to medicine. Doctors have the prospect of being able to heal all kinds of bodily damage, when the doctor, not the genes, decides how to culture them.
Similarly, the importance of the environment (within the body) in deciding how a body will grow and develop is a well studied branch of science, see morphogenesis and cell differentiation. The early embryo begins undifferentiated, and is composed of totipotent stem cells. For example, the morula embryonic stage is composed of 12-32 virtually identical cells. As rapid growth occurs, spatial differences arise, so that each cell receives differing environmental cues. Simply by being on the inner or outer region of an embryo will decide if that stem cell will produce one of the three germ layers found in mammals, from which the future sources of skin, viscera or bone will form. The stem cells react to the diffusing or cell bound chemicals in their adjacent environment. The cocktail of proteins and other molecules begin to vary in their proportions and types according to where they are located in the body. This environment determines whether a gene will be turned on to produce a bone, cartilage or other tissue, and what shape it will take. One of many possible examples is the scabrous gene in the fruit fly Drosophila (genetically, the most studied animal). The scabrous gene produces a protein that influences the number and positioning of sensory organs during neural development. If not turned on, the compound eye of the fly can become enlarged and have a confusing pattern of ommatidia, the hundreds of facets needed to make the eye. Alternatively in the wing bud, a lack of scabrous causes the sensory bristles along the margin of the wing to be missing or deformed. The scabrous gene does not pre-determine that it will affect an eye or wing. It is simply turned on or off according to localised environmental conditions in those parts of the body.
The scabrous gene does not determine that a bristle will be located exactly so on a wing. Nor in humans does a gene plot exactly where a capillary will grow. That is the role of morphogenesis, where placement is determined by the surrounding environment. That is why fingerprints, retina capillary patterns, and iris recognition patterns are always unique and different, even in identical twins. They vary in distribution not according to a map laid out by genes, but according to the logical and interactive steps experienced by cells during development. The genes cannot say where to put the capillaries. That is largely determined by the environment. After all, there are some 42,000 kms of capillaries to be positioned within the average human body.
These examples show the high level of reliance deferred from genes to the environment. The gene does not control to the nth degree, but leaves morphogenesis to the environment. Sure, those interactions within a body will occur and sequence in a highly predictable fashion, so that the gross anatomy of a human will replicate consistently to give two arms, aorta and body as we know it. But the fine detail reveals the real mechanisms and the relinquished responsibility by genes to the bodily environment for implementing growth and development. The body builds up from fine detail, and in the fine detail of a body, you can see the signs of environmental influence and the importance of spatial relationships, its ‘ecology’. Similarly, veins and arteries begin in the embryo as capillaries, and remodel due to the differential mechanical stresses that they experience due to their location in the embryo. The role of the embryonic environment is further demonstrated when cells that start to become arteries can be turned into veins, if transplanted into an opposing region, see Hirashima and Suda.
Similarly, the gene can no more place and branch a neurone than it can a capillary, and placement and arrangement of neurones is responsible for how humans think. Like veins and arms, there are gross regions of the brain that will become centres for the coordination of vision, the delivery of emotions, and musical appreciation, but again, these arise because of their location in relation to other structures, and are not pre-ordained without heavy reliance on environmental cues.
The gene shortage argument was never about denying that genes make the start for the production of hundreds of physical versions. What is important is to understand how far genes try to impose and control their productions, and when they leave the fate of the animal to its ability to interact correctly within its environment. The objectionable part of evolutionary psychology is the claim that so much behaviour is implanted by genes directly. But genes do little more than offer 30,000 or so proteins on tap to the mix, which the bodily environment then draws upon as needed according to the interactions it has. The great variety is produced by morphogenesis in a cascade of events. This cascade uses genes as the recipe, but it is a gross recipe designed to be adaptive or responsive to environmental information. In this way, the phenotype can adapt. If a child is blind, they gain heightened hearing skills. If a right handed person looses their arm, they can learn to become highly proficient with the left. There are enough genes to act as recipes, but not enough to micromanage their expression, nor do they ‘want’ to. Genes are in a partnership with the environment, and because the environment is so trustworthy, the consistent result obtained is an able bodied organism.
Like morphogenesis, the mechanism for neuronal pathway formation in response to the environment is known, and called selective stabilisation (or neural Darwinism). This is the process where some 10,000 trillion synapses in a child’s brain is trimmed to about 500 trillion useful synapses in the adult, based upon a ‘natural selection’ within the brain. Here, the production of neural pathways is according to the strengths and frequencies of stimulation received. In comparison, evolutionary psychology is a theory, arising from a limited understanding of how evolution works, and cannot prove its mechanisms (no inherited instinct has been isolated in a newborn – apart from some basic reflexes which are different to instincts). They guess mind modules must be there, deduced from their limited understanding of evolution. They see evolution as survival of the fittest (where the animal is a contained and alone individual). But a better understanding of evolution is that it is survival of the wildest (which sees the animal as being the animal plus its full compliment of environmental ties).
Environmental feedback in the cerebral cortex of the brain is varied and unpredictable. The brain is on the front line of external stimulation, more so than in the closeted environment of a body. As in morphogenesis, how can it be claimed that genes can build inherited instincts or fears in neurones, when they cannot even control the pathways of capillaries within their highly controlled internal environment? There are not enough genes to run that level of control. The cerebral cortex is like a blank slate, that receives genetic influence through a few simple desires, such as for interaction (more beetle), food, sex and water. The structures that produce these desires can be pin-pointed, and are not theory. Biology is about making use of all inputs and not wasting energy when something else will do the job for you. Biology looks for the most parsimonious way to achieve, and makes partnerships where they can be found. Cell interaction does the job of building bodies during morphogenesis. Similarly, the niche environment in combination with desire does the job of teaching what instincts should be learnt in the brain (more beetle). Biology should not fail to recognise the value of the feedback to be gained from the environment during development, in its understanding of evolution and in the role of genes. The importance of interacting with the environment should raise the profile of nature in humans. Instincts are not inherited though they entrench deeply so can offer that illusion. Instincts arise from interactions with the environment, and the synthesis of useful patterns gleaned. Evolutionary psychology promulgates the view that the environment can be ignored, as the fate of your feelings and development is already determined. My alternative view is that by shunning the full range of nature’s feedback (its most naked feedback comes from wildness, more beetle), neural development becomes stunted. As proof, look at the despair, mental state and lack of wit occurring in society today.
It is fashionable in biology to be tired of the gene vs environment debate. But it is an important understanding to get right. It will determine your outlook on the environment, and whether you see it as mother earth to be cared for and explored for its feedback and insight, or a place to be avoided or plundered (as is happening now).
Article posted 14 Feb 2007.