I’d promised a follow-up to my post on genetic paucity and the link it has to rapid extinction, as a few readers were interested in the genetic changes that happen in a captive population. Those changes mean that raising the last few members of a species to release back into the wild are very difficult, if not impossible. They are also very interesting as a model for humans, and as a window into adaptation on a global scale. I’m going to be wandering a lot deeper into the weeds of ‘what if?’ than I normally do in my science essays with this one, but bear with me.
First of all, the studies and modeling done on captive populations of different species both confirmed the hypothesis that yes, keeping animals and organisms in cages (so to speak in some cases) changes them. What seems to have shocked the scientists is just how fast that can happen. Domestication of animals is long known to have affected species in odd and wonderful ways – just look at the dog, for instance. There are hundreds of variations on Canis domesticus, which all descend from a now-extinct canid, not the wolf as was commonly believed. Shadowdancer shared an article about the effects on foxes when they are kept and bred in captivity, things like coloration changes, tail configuration changes, things you wouldn’t assume would happen just because they were removed from the pressures of the wild.
The study I had seen on the Cabbage White Butterfly had looked at changes that were potentially fatal in the wild. Butterflies raised in cages grew smaller wings, heavier bodies, and laid more eggs. The net effect of all of those was a butterfly that could fly less, slower, and while more eggs means larger population, it makes the females even more vulnerable to predation due to the added mass slowing them even more. The population was chosen for the study because there was a large extant wild population (the caterpillar of Pieris brassicae is a common pest) to compare with a population that had been raised in captivity for between 100-150 generations. The implications for captive animal populations are clear: being held captive will change you.
Just how long until we see an effect? Well, in studies done on Drosophila, a common model organism, a doubling in fecundity was seen in only eight generations. Eight. In human terms, using the rough rule of thumb of twenty years to a generation (arguably this could be telescoped further, as I’ll discuss shortly), that’s a mere 160 years. Which means, in genetic terms, that the United States of America has existed for more than long enough to affect the genes of those who are born to it. Granted that a fly is not a human, but the model organisms give us ways to look at genetic adaptation over many generations in a way that, say, raising elephants cannot. But elephants are not immune from this, either. It’s simply that it would take longer to see the adaptations as their generational span is vastly longer than a fly or a snail or even a fox.
The implications for successfully re-wilding a captive population are clear: that which we return to nature is not what was there to begin with. As I mentioned in my earlier discussion of this, there is some argument for the pointlessness of attempting it, as extinction is a natural and normal process. However, exploring the concept further, we find wild horses, and humans.
I grew up with mustangs. I read books about wild horses, I dreamed of seeing them running wild and free, and when I was six, my mother ‘adopted’ a mustang from the BLM (which will always mean Bureau of Land Management to me, no matter the modern attempt to co-opt the acronym). That was the first of several mustangs to come live with us, and they only fueled my interest in the wild horses of the west. Pre-Columbian era, there were no horses in the Americas. Or rather, there had been, but they had become extinct. The saying among the peoples of the Americas who joyously adopted the horse as quickly as they could was that ‘the grass remembers the horse.’
The horses who were brought to the Americas, and who quickly re-populated it, were not, of course, quite the horses who were discovered later to have been here, through investigation of the fossil record. But they were close enough that they could walk into the ecological niches and start grazing. They fit in well. Later, much later, the scrubby wild horses that had survived in the centuries between the 1500s and early 1900s were joined by a fresh influx of genes in the form of horses no longer needed on farms who were simply turned out to join the wild ones. Any kid who has read up on Misty of Chincoteague, Dick Francis’s racing mysteries, and other books of that sort, is aware that there are wild herds and tame from coast to coast in the USA, and that they are all different. They have adapted to their environment, from the high-altitude ponies of the Andes to the delicate long-legged thoroughbred of the Kentucky bluegrass.
Horses came back from extinction through the path of captivity. Their passage changed them, formed them into what they are now, so you can trot a Shetland up to a Clydesdale and wonder if they are the same species (they are, although you’d have to use artificial insemination, the draft mare, and some wild-eyed wonder to see what came of it). Humans haven’t varied quite that much. Yes, there are superficial differences, but it’s more the internal I’m interested in.
Remember how the captivity changed the butterfly? There was a conversation among friends a while back, I don’t recall exactly who all was taking part in it, but something that came up caught my imagination and left me wondering. How much does living in our increasingly urban coasts affect the genetics of humans? Does, for instance, the obesity ‘epidemic’ have as much to do with the loss of pressure of hunger and adversity? The butterflies, freed of the need to fly away from predators and hunt for food far and wide, became less fleet, fatter, and able to have more babies. Our genes are shaped much more by our heritage than we once thought – the field of epigenetics is just now starting to unfold. What does this urban lifestyle do to us? I’m not suggesting that we need to flee cities – I’m not fond of them, but they are a useful tool – I’m simply wondering what if we also adapt? What if we change in captivity? What comes next?
What is happening elsewhere in our world? Generation telescoping means that if a baby is born to a mother merely 15 years of age – not unheard of in cultures and countries on this globe of ours – that eight generations can collapse to 120 years. In other words, 1900 to now. That’s… not a lot of time, relative to known history. We are a changing species, but into what?
We no longer have an easy frontier to challenge our adventurers. The genes of pioneers are an interesting quandary: where do the Odd go when there are no more fringes of society reaching out into the unknown? I look upward at the stars, knowing that’s the last hope. Captivity in animal populations is recommended to be ‘fragmented’ or given many different places to breed in, and then those populations to be crossed back in order to foster genetic diversity and slow the adaptations to captivity that would be fatal to a wild population. Humans, right now, don’t have that luxury. We’re very nearly a global population and that last bit of a gap is closing fast. We need to fragment, too. Which means we need to make a giant leap off this mudball and upward to the stars and the potential to change and adapt and reach for the next big thing out there, somewhere.