By Marco Arturo
Anoles are a diverse group of lizards native to the Americas, which present a wide range of adaptations according to their niche. You’ll find anoles with quite long and muscular legs, helpful for gripping tree trunks, as well as some with tiny legs adapted for life on small twigs.
Agroup of scientists led by Professor Jonathan Losos experimented on small, lizard-free Caribbean islands monopolized by thin branches and twigs. They introduced two species; the brown anole, whose long legs help it run on trunks and thick branches, and the larger, predatory curly-tailed lizard, which is adapted for hunting on the ground. The researchers found that in just six months, the brown anole’s average leg length increased, so as to run away from the curly-tailed lizard more efficiently.
But soon after that, the opposite had started to happen: their legs became significantly shorter to make them fitter for life in the twigs. In just a year, the most impressive phenomenon in the known universe, responsible for the diversity of the 350,000 known species of beetles, the majestic sequoias, and antibiotic resistance manifested itself: evolution by natural selection.
A common misconception is that animals, such as anoles, evolve. But Harold the brown anole’s legs didn’t grow nor did they shorten over his lifespan. No, populations evolve. Our genes are a set of instructions for how to make a copy of ourselves. But this is far from perfect – when cells divide, around 120,000 copying errors are usually made. This is why you’re not an identical copy of your sibling. Actually, ever met a group of a suspiciously large number of siblings? They’ve all got their own thing going on; one is quite tall, one likes math, one has three times the muscle mass of another, and one is just like yourself… I don’t know what your thing is supposed to be, honestly.
Who do you think the birds were more likely to spot now, huh?
The same differences are noticeable in any set of siblings, ever; there’s quite a bit of variation between descendants of trees, frogs, fungi, and yes – anoles. When they reproduced on the island, their offspring presented quite a bit of morphological diversity. Even if none of them liked math, a few were born with copying errors that made their legs longer and those were the ones who didn’t get eaten, hence the only lizards who could pass their genes to the next generation. The same principle applied when the opposite took place, those born with small legs were better suited to their environment so they had a higher chance of reproducing.
Although evolution is often thought of as a force that drives organisms forward in a linear path towards perfection, scala naturae (or ‘ladder of nature’) as it was called, this isn’t the case at all – it’s just a rule that says ‘be born with a random mutation that happens to make you better suited to your environment, or die’, and the result leads to a noticeably branched phylogenetic tree.
The pepper moth is a great example of this. It evolved a white color to camouflage itself on the lichen-covered trees. A black morph of this species, again caused by a random mutation through the beautiful mechanism of copying errors, never quite got its chance, since birds could easily spot them against the white lichens. During the Industrial Revolution, pollution in England caused many of the lichens to die out, leaving just the dark color of bare wood instead. Who do you think the birds were more likely to spot now, huh? Those moths with a copying error that made them dark-colored soon became the ones with a higher chance of passing their genes to the next generation, effectively becoming the norm.
Evolution through natural selection is, by all means, severely under-appreciated. Not only due to its rejection by pretty much every major system of belief (all of which would in fact be enriched by incorporating such a marvelous process into their ideas), but also because most people aren’t fully taught the simple yet wonderful mechanism through which it operates. The understanding of said process makes it an axiom, just too obvious. As the geneticist Theodosius Dobzhansky famously said, “Nothing in biology makes sense except in the light of evolution”.
However, what’s really cool is that it also applies the other way around – everything in biology makes sense in the light of evolution. Just think of any feature of any living being and you can deduce the basics of how it came into being. The early hominids who were born genetically predisposed to be scared of the dark both avoided it and prepared to respond to the threat of a predator, so they were the ones most likely to live long enough to reproduce. The hognose snakes born with an instinct to roll over and freeze when confronted by a predator tended to be left alone, assumed dead. The wolves that instinctively responded to fast-moving small objects by chasing them hunted the most prey, and that’s why our dogs like to play ball.
When the principle of natural selection is applied to animal behavior, it’s easy to see why zoology deals with the most complex and fascinating collections of atoms in the known universe. It’s hard to find something more phenomenal and awe-inspiring. Us animals are the universe’s way to feel, to know, to love, to think, and to understand the beautiful process in which we all try to maintain a firm grip on our thin branch on the tree of life.