Wednesday, February 28, 2007

Biological time

(Short discussion of timescales from a biological perspective, a contribution to a discussion no longer remembered about something else, Mattias Forshage, early 2006)

Of course there are a great number of different biological timescales, some of them fairly constant throughout the realm of life (speed of nerve impulses, annual cycle, daily cycle), some widely varying in acordance with the lifestyle of the specific organism, some more long-term and dealing more with development of lineages rather than individual organisms (that is, phylogeny rather than ontogeny).

The most important time unit in evolution is the generation time, which ranges from minutes in bacteria to decades in large vertebrates like man (a good median is perhaps one generation per year in most insects in temperate climates, annual plants, most birds, etc). Over a number of generations evolutionary change can occur. It is very difficult to specify how many is needed. Only in bacteria we can directly observe evolution, and what we see there is obviously very different from what goes on in most animals as there is no sexual reproduction, meaning that there is neither any recombination of the genetic material (thus less change) nor any spontaneous ”censorship” in simple non-fertilisation or spontaneous abortion (thus more change). Evolutionary timescales is one of the questions in the 70s-80s debate between more leftist-hegelian ”punctuated equilibrium” (”saltationism”) and more rightist ”gradualist-adaptationist” views of evolution. From a poetic viewpoint it will suffice to imagine evolutionary time as vastly longer than human experienced time. If we stick to the gradualist stories it’s all extremely slow, if we try the saltationist version it will vary between millions of years of practically nothing happening and then sudden bursts of activity in response to certain threshold geological events like forming and breaking of land connections, elevation of mountain ridges, major volcano eruptions, drying of wetlands, rivers making new turns etc.
Experienced time is a totally different thing, and of course it’s often far easier to spontaneously vividly imagine when watching different animals. Obviously heartbeat rates, metabolism and speed of thought vary even within our own species, but within a fairly narrow range. Small endothermic animals (like sparrows and mice), as well as larger herbivores under heavy predation pressures (all those deers and antelopes etc), generally live faster, with faster heartbeats and shorter lifespans. A lot of the former hibernate when living in cool climates, meaning that they drastically slow down all bodily processes, and thus time as such, during the winter. Large ectothermic predators (like crocodiles and large snakes) have perhaps the most dramatically fluctuating sense of time, being able to strike incredibly fast if they are hungry when a prey is near, but then wait and actually do nothing at all for a year or more. Also for smaller ectothermic vertebrates like fish and lizards, it’s quite obvious that they spend a lot of time doing nothing whatsoever but when they move they do it real fast. This truly fluctuating sense of time is a totally different thing than the mere monumental laziness required by those mammals that just sleep throughout the whole winter rather than truly hibernate (like bears), or the more humanlike sense of variation, creating a continous interplay between leisure/boredom and enthusiasm/stress, that we see in most primates and carnivores.

Speed is obviously one of the issues connected with the endothermy, the internally regulated, constantly high, body temperature of birds (and we don’t know which ones of the dinosaurs preceding them) and mammals. A consequence of this is that the capacity for speed is the plesiomorphic (inherited) state in birds and mammals, so that slowness is the phenomen requiring a particular explanation wherever it occurs. Slow birds are very rare, and even rarer after the extinction of the dodo. A heron is certainly not slow but a murderous parttime freezer of the same kind as other stalking hunters like praying mantises. The only slow bird I come to think of just now is the south african ground hornbill, slowly walking about investigating the world and not fearing anything. Among the mammals only few, like the leisure-pleasure swimmers manatees & dugongs and the truly timestopping canopy grazing sloths, are perpetually slow. Most others, be it pangolins, armadillos, cattle, elephants, rhinoceroses or hippopotamuses, just prefer a slow pace manifesting that they don’t have to be afraid, and they’re all quite capable of swift movement whenever needed.

Experienced time of non-vertebrates is a different affair. As most of them don’t have a rhythmically beating heart, or a really information-storing brain, time becomes more of an automatic, but chaotically complex, interaction between temperature, nerve impulse speed and external stimuli. (often leading to dead ends, like flies at a window or moths at a lamp). So much more difficult for us to get a picture of what they actually experience. In dung beetles, speed is mostly a simple product of surrounding temperature, they behave exactly the same but quicker when temperature rises. Common large predators like spiders, ground beetles, centipedes, ants and dragonflies have the same rush and rest dualism as in the vertebrate predators. The movements in the rushes are way beyond us but the pattern is simple. Worse are insects like the common house fly, extremely fast for reasons that don’t appear obvious to us, making pointless rushes and inbetween that sit and brush themselves in a strangely jerky and ritualistic way. However, apparently lacking a sense of time themselves, they keep manifesting these endless repetitions and vain labors that make human spectators so extremely frustrated. And the mayflies have no anguish whatsoever about the fact their adult timespan will be prolonged further than a mere few hours only if weather is too bad for flying. Other animals like social wasps (bees, ants etc) and octopus do obviously do more complex information processing and have some sense of time, but while the hymenopterans always turn out to be disappointingly boring whenever some aspect of their language is interpreted, the cephalopods remain simply unintelligable.

And once into weird examples, let’s cite the the north american prime number cicadas, with a larval development time span of strictly 13 or 17 years. Some vascular plants will blossom more rarely than that. And the pantopods (sea spiders), marine stalkers of the extremely wary bryozoans, who pull their tentacles back into the shell immediately when something happens nearby, so the pantopods can’t rush on them but just walk real slowly and devour them just as slowly! And of course the tardigrades (water bears), slow crawlers in most habitats and weathers, but whenever temperature drops below zero or all water evaporate they just fall into a deep coma, without any life signs whatsoever, and stay that way until environment becomes suitable again, when they just resume business as usual, even if they were as dead for centuries inbetween!
Vascular plants are rather mysterious too whenever you try to think into their worldview. Even though all fast movements of plants are mechanical processes requiring no nervous input, they do have a well-developed fast nervous system, they do detect pain etc, only no one knows what it really means to them.

But, whither we wanted to get was the timescale of creativity and dynamism in habits. This depends mostly on the type of lifestyle. Both genetic evolution and cultural evolution are about unique historical events, but the general conditions for genetic evolution are far more restraining, as most events in the life of the individual organism simply don’t affect it. Cultural evolution can be far more dramatical. Some traits are of the cultural evolution type (not genetically handed over, and thus either phylogenetically constrained or not) without necessarily having anything to do with culture, like geographical distribution areas, habitats, food and host-parasite relationships. Just like behavioral traits, where it’s ususally unknown to what extent the basis is genetical and indeed very often meaningless to pose that question at all without recognising the fundamental interdependence of environmental and genetical conditions, we can only determine the mode of inheritance, and thus the timescale and the amount of phylogenetical information involved, a posteriori.

So, several organisms have a lifestyle which requires them to be curious and inventive and seek variation and novelty. There is certainly a genetic basis for this openended flexibility, and it may perhaps even be described as a paradox, to be genetically programmed not to stick to any programming! In mammals and birds, this is true for non-specialised predators (cats, dogs etc) and omnivores (pigs, crows, rats, bears, a lot of monkeys & apes including man), and it’s also true for social species with a fair amount of cultural evolution (and thus dynamic societies rather than the static ones of ants, bees and termites) (examples being dolphins and other whales, horses, elephants, and again dogs and many monkeys & apes including man). Thus the notion of natural creativity is closely linked to what we usually call intelligence, but it only partly overlaps the notion of eusociality. (There are also weird animals who developed these creative traits for totally different reasons, usually rampant sexual selection (nests of bower birds, song of starlings and other improvisors, etc)). So humans is among those who have dual reasons to be curious-dynamic. This natural creativity is certainly situated on the timescale of the experienced time of the individual organism. A sudden discovery or invention one day may change ones life and affect the lives of ones successors. Again if we like paradoxical statements we can say that it’s natural for human beings to be unnatural.

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