The Power of Cultural Selection
Two years before Charles Darwin embarked on his paradigm shaking voyage to the Galapagos Islands another famous naturalist and proponent of evolution lay on his death bed. For all of his many accomplishments, biologist Jean-Baptiste Lamarck is remembered, and usually ridiculed for his hypothesis on the inheritance of physical features. He proposed that the physical strengths an animal developed during its life were passed on in its genes to its offspring, picturing the evolution of an animal like the giraffe as the result of stretching up to strip leaves from a tree and developing a longer neck, then passing that longer neck on to the next generation.
Today it’s broadly accepted that your own weight lifting won’t make your kids more muscular, though some epigeneticists might beg to differ. But most genetic science now concludes that your exercise patterns won’t remake the genes you pass on. One thing you can pass on to your descendants however is your culture, and your culture will profoundly effect how their bodies and their brains develop.
Culture had been assumed to be one of those markers of “humanity”, like language and tool making. Closer examination of animal behavior over the last several decades though has blurred some of these once clean, bright lines. Jane Goodall first observed tool making among the chimpanzees that she studied, and put a different spin on the phrase “man, the tool maker”. When she observed how her subjects passed the skills of tool making and tool using down through the chimp generations our exclusive ownership of culture started to look less proprietary as well.
We easily accept the concept of sexual selection as a driver of evolution but then often dodge behind the non descriptive term “instinct” to explain this and many other complex animal behaviors, actually to explain them away.
Instinct supposedly leads migratory waterfowl to undertake their epic semi-yearly journeys. Examples abound however of migratory birds that quit traveling and settle down in a comfortable year long venue. The docu-drama film Fly Away Home, for example, details the efforts of a girl and her dad to teach a clutch of adopted goslings to migrate, using techniques developed by wildlife rehabilitators to teach endangered whooping cranes the same supposedly instinctual act.
These examples should make obvious the fact that migrating waterfowl learn to migrate, probably from following the older, wiser members of their flock; it’s in their culture. They have the dedicated brain architecture to navigate long distances and the physical capacities to fly many hundreds of miles without rest, but if “instinct” was driving them to fly north in the spring they wouldn’t be willing to park and graze all year on my golf course.
Decades ago a popular book, Born Free, told the story of Joy Adamson and her husband George, who raised an orphaned lion cub and returned her to life in the African wild. Elsa the lion cub may have inherited the common cat behaviors, chase/pounce/bite, but joining a wild lion pride proved to be a lot more complicated than cat’s play. It’s difficult to point to any animal inhabiting a complex environment who doesn’t go through a period of training from at least one parent, if not from an extended social group. The use of learned behaviors, from herd grazing and seasonal migration to cooperative hunting and enforced territorial claims, should exert strong selective forces on the populations involved. I would suggest they apply a force of selection strong enough to drive the origin of species.
That early short pre-giraffe stretching up to graze the higher leaves found a relatively rich, untapped resource or niche in the process. She almost certainly taught her offspring and her herd members to do the same, and in doing so likely set off a behavior driven cascade of selection. With an ever larger group now focusing to some degree on reaching up to graze, individuals with longer necks and longer legs that granted them advantage in this new strategy were more successful. This, according to standard ideas of natural selection, should have granted them advantage in breeding selection and success. As these taller individuals were more often paired, the genetic algorithms that created their tall stature were reinforced and amplified, the same way that pigeon breeders could select and amplify the traits in their outlandish birds. The race was then on between the ever taller giraffes and the acacia trees on which they fed; the selective success of the giraffe’s behavior creating ever taller giraffes and in turn the higher grazing of the giraffes forcing the acacias to lift their canopies to get back out of reach.
Seals are believed to be descendants of dog like animals, and one has to wonder how they could transition from land hunting omnivores to elegant swimmers and pescatarians. In a gene driven hypothesis, some sort of genetic variation would have induced the lucky dog possessing it to swim and hunt in the sea. In a culture driven hypothesis however the behavior would come first and the adaptation would follow. It’s certainly possible that an individual recognized in themselves a physical trait granting marginal advantage in the water, and then followed that trait into an aquatic lifestyle. This succession of events seems less likely though than a strongly behavioral one.
Most animals lack the degree of self awareness necessary to first observe a physical trait in either themselves or other members of the group and then apply this knowledge to gain an advantage in a novel environment. Each member of pack or herd has a well learned role in their cooperative activities. The random presence of a physical trait better suited for different task would likely go unnoticed, or prove to be be a disadvantage in the traditional group culture and be selected against.
If the behavior came first however, if an individual or pack discovered an untapped resource along the shore, perhaps in a set of tidal pools, the selection dynamic would change. Dogs are skilled at recognizing and exploiting food resources, even novel ones in novel situations. If a population encountered and sampled a rich and untapped food source, the benefits of diving in to claim that resource could outweigh the cost of inadequate adaptation for the dive. If the reward was rich enough it could actually expand the range and accelerate the pace of variation, creating new physical options to adapt the population to the activity.
The dog’s ability to learn and master complex environments is a skill set that bears real fruit when opportunity presents, and is not a trait unique to dogs. When a new environment offers significant increases in resources it can widen the fitness horizons for the population that finds and exploits it. The more generous the new resource base, the more leeway there is for variant individuals to survive, and the more variation thus allowed and exposed in the population. Broadening the bell curve of fitness allows new pairings of individuals formerly selected against in breeding, pairings that can reinforce and amplify outlier physical traits. When paired and amplified these outlier traits can strongly shift the physical norms in a population, shifting the selection horizons that population faces in turn.
The “special sauce” necessary to drive large divergences in physical form, to create distinctive new species, is abundance. Darwin based much of his theory of the origin of species on just the opposite, on scarcity and the “nature, red in tooth and claw” competition for scarce resources. When Darwin landed in the Galapagos Islands he walked onto a relatively sparse and harsh environment. These islands not only underwent seasonal restrictions on rain and seed production, but also endured longer periods of drought related to the El Nino/La Nina ocean temperature cycles, poverty stacked on poverty.
What Darwin couldn’t see was the relative plenty that greeted the first finch colonizers on the islands. Possessing seed producers but uninhabited by finch type seed feeders, the Galapagos presented the first colonizers with many open niches, open opportunities for adaptive radiation. The first years of finch colonization were likely filled with resource discovery and creative opportunity, ripe with adaptive paths for the pioneers to punctuate into new species.
Darwin largely pictured animals as more mechanistic creatures than we do today, driven by unconscious instincts, limited or enabled by physical features and the genes that created them. Giving little credit to intelligence, creativity and sentience among his subjects he focused instead on an inheritance, gene driven model of divergence. His model of the origin of species emphasized the marginal advantages granted by genetically created physical traits as the drivers of individual behavior. He hypothesized that tooth and nail competition among individuals, for limited available resources in long term stable environments, forced competing populations to either diverge physically to lessen competition, or to face extinction.
Research on the Galapagos Finches has noted and quantified this kind of forced divergence among competitive populations, and noted as well that it only caused them to diverge within a narrow range of physical attributes. The competing populations tended to share resources when times were fat and only focused in on the foods closely suited to their specialized beaks when forced to do so by drought and hard times. While tough competition seemed to have start their process of divergence it also seemed that the reach of such specialization was strictly limited by the wealth and reliability of the resource exploited.
To make a dramatic departure in form, from dog like creature to seal or from low level browser to giraffe, a dramatic reward may be necessary.
It’s entirely possible that the early giraffes did evolve from a slightly taller early individual or family gifted with the genetic opportunity to seek higher leaves. It’s possible that competition with other grazers did drive the upward search for untapped resources. But given the ability of most animals to observe, copy, and adopt the strategies of flock or competitors, it seems unlikely that only those with marginal height advantages would seek a new and rich resource when opportunity arose or need demanded.
What seems more likely is that giraffe innovators initially drove the selection process, adopting a new feeding strategy that rendered rich rewards and which put the existing funds of variability in their population through a new selective sorting. As parents taught this new strategy to their offspring the taller among them were more successful, and as the more successful individuals paired off and bred they matched up more of their algorithmic codes for features of giraffe height, from longer legs and necks to more powerful circulatory systems to pump blood further uphill. The model of our pigeons or dogs is instructive here.
When pigeon breeders selected slightly variant individuals possessing a degree of divergent traits and interbred them, those traits ballooned far beyond their expression in the original parents. There’s no reason to think that this effect of matching and thus amplifying algorithmic codes is exclusive to pigeons or dogs. The success of taller proto giraffes and their pairing with similar mates may have had less selective drive than the conscious choice of the pigeon breeder, but it may also have been just as quick and certain. We have the fossil evidence for instances of punctuated equilibrium that seem to track rapid physical changes; we have the example of large divergences in form quickly bred into our dogs and pigeons. It would seem that the known shape-changing ability we have already observed in animals matches up nicely with the “punctuated” shape changes we observe in the old bones.
What sort of factors would change the behavior of a population of early giraffes or seals? First and most obvious would be changes in weather or climate patterns that forced or allowed migration into new territories. An event like this is now postulated as the cause of the evolution of the latest version of modern humans. 70,000 years or so ago, a prolonged period of drought and desertification in Africa is thought to have driven a population of pre sapiens hominids onto the western coast of the continent. This ocean side area possessed a rich menu of food resources that allowed them to settle into a relatively small area and satisfy food and shelter needs with relatively little effort.
The new found bounty is thought to have fueled a burst of creativity in language use and in cultural pursuits, a birth perhaps of art and aesthetics, accompanied by physical changes that characterize modern humans. Members of this group are hypothesized to have then migrated back across Africa, Europe, Asia, and out on the Pacific Ocean, displacing and at times interbreeding with Neanderthal populations.
This kind of scenario has probably played out countless times in the history of life on earth. For the giraffe it could have been a move onto savannah type areas with scattered trees that invited them to turn their graze upwards. For the ancestors of the seals it could have been the characteristic ranging of young adults from the pack into new territories that met up with the rich tidal band of an ocean.
For Darwin’s Finches it probably was something like a storm that blew a migrating flock five hundred miles off course from the coast of Ecuador to an archipelago colonized by plant communities but possessing no finch type seed feeders. Their adaptive radiation to exploit different size seeds, insects, and cactus flowers would have been both enabled and perhaps limited by the degree of algorithmic variation already stockpiled in their small colonizer population, and by the rate of natural mutation of those algorithmic codes. But more importantly, that range of that radiation would have been limited by the menu of reliable and rich niches that were open to exploitation.
When Darwin first observed the finches he didn’t notice the minor differences between the birds on each island and assumed that each island had its own separate species. The differences that escaped his eye have led biologists now to classify the birds as a dozen or so distinct species. The degree of limits on the wealth of their new environment probably limited the degree of possible dramatic physical departures from each other as well.
Contrast the frugal departures in form in the Galapagos finch to the Drepanididae of Hawaii, which radiated into more than 40 distinctive and easily distinguished species, and made up only a little more than half of the total endemic Hawaiian species before human encroachment and exotic invaders drove many to extinction. The Galapagos have a third as many endemic species as the Hawaiian islands, and half of those are direct radiations of finches, so alike in form that many can only be distinguished by an expert eye. The crucial difference in the species density and degree of variation shown on the two island sets seems to be the poverty or richness of the habitats available to the colonizing populations.
Hawaii’s Drepanididae have departures in coloration, bill structure, size and feeding habits that dwarf those of the Galapagos finches. Not surprisingly, Hawaii has reliable and diverse food resources that aren’t whipsawed by drought and flood. A finch colonizing Hawaii would have found a staggering array of available seeds and flowers, resources that didn’t disappear on an unpredictable timetable. Changing shape to specialize on just a couple of these came with little penalty of periodic and unpredictable poverty.
For the Galapagos pioneer, specialization to exploit a particular resource could lead to disaster when that resource was restricted in the next El Nino cycle. Periodic poverty necessitates conservative strategies. Sexual selection, for example, takes very different forms on the two archipelagos. Darwin’s Finches vary little in color and show readiness to breed by merely darkening feathers and bills. Hawaii’s Drepanididae on the other hand often display brilliant breeding colors, an investment made both possible and necessary by the wealth of their environment.
Not only has specialization in form been rewarded in the Hawaiian isles, it has been rewarded so richly that its beneficiaries have had to, and could afford to spend heavily on sexual displays in order to win a mate. For the Darwin’s Finch such extravagance was simply beyond their means, and a near certain deadly investment when times got tough, as they inevitably did.
While the beaks of the Galapagos finches are the distinguishing features that divide them into species, their divergences are often measured in fractions of millimeters. The taxonomists and the birds themselves can see the differences but those differences are subtle enough to fool the uninitiated, like Darwin. The beaks of Hawaii’s Drepanididae, in contrast, have diverged in extravagant diversity, with the long slender and downcurved bills of several different nectar feeders standing out. Some of the Hawaii birds have developed beaks similar to those found in the Galapagos, stout seed crushers, more slender and pointed versions better suited to insect and fine seed gathering, but no bird on the Galapagos has anything resembling the inches long curved probes found in Hawaii.
So, the two models of adaptive radiation and dramatic divergence in form seem to be demonstrated in these two archipelagos; tough competition for scarce resources with small variations determining the outcome on the one hand, opportunity driven exploitation of bounteous wealth, on the other. Darwin’s scarcity and competition model seems to fit the conditions on the Galapagos but has led to only minor and subtle divergence among his finches. The wealth driven divergence utilizing reinforced and amplifying algorithmic codes seems to fit the Hawaiian islands.
It’s hard to argue that the inhabitants of either archipelago don’t, or didn’t utilize sentient and culturally transmitted behaviors to pursue their livelihoods, that the nectar feeders in Hawaii had to wait for a bird with a freakishly long bill to start seeking nectar. The Galapagos nectar feeders have developed only slightly variant beaks to facilitate their sipping, beaks that are still useful for harvesting other food sources. The Hawaiian nectar feeders, on the other hand sport extravagantly curved beaks that are useful for little else. While it’s possible that a population with such extravagant beaks was blown by chance to Hawaii, the more likely scenario is that more generalist birds first populated both island chains but that only the Hawaiian islands would support such divergent specialization.
Neither Lamarck nor Darwin had access to any significant information on the nature of genes, of genetic variation, or even of the cellular level operations of sex and the ways that sexual reproduction allocates genetic material to the next generation. Even our own understanding of animal behavior has undergone dramatic discovery and revision in just the last couple of decades. It’s hard to know how they would have integrated such knowledge into their theories but I suspect that Lamarck would have taken great interest in recent revelations about the apparent cultural behavior in animals. I can see him arguing, “See, the act of stretching up for leaves does lead to offspring with longer necks…just not exactly the way I pictured it”.