Quotes About Biology

In that case there must have been genes controlling variation in caddis houses, for selection cannot produce adaptations unless there are hereditary differences among which to select.

Natural selection may usually be safely regarded as the differential survival of replicators relative to their alleles.

Once the vital ingredient—some kind of genetic molecule—is in place, true Darwinian natural selection can follow, and complex life emerges as the eventual consequence.

We are fundamentally interested in natural selection, therefore in the differential survival of replicating entities such as genes. Genes are favoured or disfavoured relative to their alleles as a consequence of their phenotypic effects upon the world. Some of these phenotypic effects may be incidental consequences of others, and have no bearing on the survival chances, one way or the other, of the genes concerned.

The word allele is nowadays customarily used of cistrons but it is clearly easy, and in the spirit of this chapter, to generalize it to any portion of chromosome.

This, then, is our candidate replicator. But a candidate should be regarded as an actual replicator only if it possesses some minimum degree of longevity/fecundity/fidelity (there may be trade-offs among the three).

An arbitrarily defined length of chromosome, or potential replicator, may be said to have an expected half-life, measured in generations.

Phenotypic effects of genes, whether at the level of intracellular biochemistry, gross bodily morphology, or extended phenotype, are potentially devices by which genes lever themselves into the next generation, or barriers to their doing so. Incidental side-effects are not always effective as tools or barriers, and we do not bother to regard them as phenotypic expressions of genes, either at the conventional or the extended phenotype level.

But if we set selection pressures on one side, we can say something about the half-life of a replicator on the basis of its length alone. If the stretch of chromosome we choose to define as our replicator of interest is long, it will tend to have a shorter half-life than a shorter replicator, simply because it is more likely to be broken by crossing-over. A very long portion of chromosome ceases to deserve the title of replicator at all.

It is widely admitted that serious error follows from the uncritical assumption that adaptations are for the good of the species.

To try to make a man, you would have to work at your biochemical cocktail-shaker for a period so long that the entire age of the universe would seem like an eye-blink, and even then you would not succeed.

Natural selection favours those genes that manipulate the world to ensure their own propagation. This leads to what I have called the central theorem of the extended phenotype: An animal's behaviour tends to maximize the survival of the genes 'for' that behaviour, whether or not those genes happen to be in the body of the particular animal performing it.

However, we must expect lies and deceit, and selfish exploitation of communication to arise whenever the interests of the genes of different individuals diverge. This will include individuals of the same species.

although evolution may seem, in some vague sense, a 'good thing', especially since we are the product of it, nothing actually 'wants' to evolve.

The flagellar motor of bacteria is a prodigy of human nature. It drives the only known example outside of human technology of a freely rotating axle.

The evolutionary importance of the fact that genes control embryonic development is this: it means that genes are at least partly responsible for their own survival in the future, because their survival depends on the efficiency of the bodies in which they live and which they helped to build.

However small the minority of planets with just the right conditions for life may be, we necessarily have to be on one of that minority, because here we are thinking about it.

You may have heard that DNA is a 'blueprint' for a body, but that's deeply wrong. Houses and cars have blueprints. Babies don't. The difference is entirely separate from the fact that cars and houses are designed whereas babies aren't. Here's the deeper difference. In a blueprint there's a one-to-one 'mapping' between each bit of the house (or car) and each bit of the blueprint.

Natural selection favours genes that control their survival machines in such a way that they make the best use of their environment. This includes making the best use of other survival machines, both of the same and of different species.

Kamikaze behaviour and other forms of altruism and cooperation by workers are not astonishing once we accept the fact that they are sterile. The body of a normal animal is manipulated to ensure the survival of its genes both through bearing offspring and through caring for other individuals containing the same genes.

The gene's extended phenotypic effect, say an increase in the height of the dam, affects its chances of survival in precisely the same sense as in the case of a gene with a normal phenotypic effect, such as an increase in the length of the tail.

The second point of this present chapter is that the genes that bear upon any given extended phenotypic trait may be in conflict rather than in concert with one another.

If two beavers working on the same dam have different genes for dam height, the resulting extended phenotype will reflect the interaction between the genes, in the same way as bodies reflect gene interactions.

Within each species some individuals leave more surviving offspring than others, so that the inheritable traits (genes) of the reproductively successful become more numerous in the next generation. This is natural selection: the non-random differential reproduction of genes.