Sometimes I ask myself, “Why am I thinking so deeply about evolutionary theory while I’m sitting on a bus on the way to my retail job? What good can it do?” But I continue regardless. Because I am hopelessly fascinated by the subject. And while it’s much more fun to think about the evolution of wings for flying or claws for digging or teeth for grooming, I often settle into more serious pondering, on the subject of evolution in modern Homo sapiens sapiens.
OR LACK THEREOF?
When I start to talk to someone new about evolution, I often get myself into an unfortunate argument–not intentionally, of course. Many perfectly intelligent people believe that as a species, human beings are no longer evolving. Immediately, to me, this notion is preposterous. And besides that, it is a sad illustration of how misunderstood, perhaps badly taught, are the key concepts of evolutionary theory.
Allow me to direct the reader to some definitions of evolution from the web. (Thank you, Google’s “define:” feature!)
EVOLUTION
- development: a process in which something passes by degrees to a different stage (especially a more advanced or mature stage); “the development of …
- (biology) the sequence of events involved in the evolutionary development of a species or taxonomic group of organisms
wordnet.princeton.edu/perl/webwn
- In biology, evolution is the process of change in the inherited traits of a population of organisms from one generation to the next. The genes that are passed on to an organism’s offspring produce the inherited traits that are the basis of evolution. en.wikipedia.org/wiki/Theory_of_evolution
Then there is the academic definition I learned in my genetics classes.
EVOLUTION IN MODERN CONTEXT
Hopefully it is apparent now that evolution is not simply survival of the fittest, even if that is a very large part of it. Evolution is a constant process. Every population, species, genus, family, and so on, is evolving as I write this. Only extinct groups don’t evolve. Even if we cure all diseases, the process of evolution will continue in our species. You can think of alleles as little genetic differences between individuals or groups of individuals. Some allele differences are readily observable, such as eye color, and some are not. When a baby is born, it contains some of its mother’s and some of its father’s genetic information, thus changing the frequency of alleles in its population. Instantly. This is a very simple illustration, and may not seem very useful in studying evolutionary change over time, but it is the unceasing births and deaths within a population that allow evolution to continue. Heritable mutations in turn add to genetic diversity.
So what is the significance of these miniscule changes in allele frequency? Remember that selection can be positive, negative, or neutral. When a completely healthy person dies without having had a child, his or her genes have been selected against. Likewise when a person with a genetic disposition toward heart disease has a child, his or her genes have been selected for. In our modern society, evolution appears to have stagnated because selection is generally neutralized by medicine and good nutrition. Genetically “fit” individuals do not always pass on their genes because they have access to birth control and do not need extra hands in the field to keep the family fed, or to take care of them in their old age. Genetically “unfit” individuals can pass on their genes because of treatments, cures, and suppression therapies.
Consider in addition the sheer size of our population and how open and fluid it is, allowing foreign genes in and sending native genes out, and you should understand why large-scale evolutionary changes aren’t occuring here. There is simply no overwhelming push one way or another.
EVOLUTION YOU CAN SEE
Hundreds of years ago, people lived shorter lives, and generally didn’t grow as tall as we do today. Whether that is proof of genetic change, or just of better medicine and improved diet, is up for debate. Evidence of large-scale evolutionary change in modern humans since history began is scant to invisible. But evolution is not all about large-scale change. In humans, the process is probably just too slow to observe.
In my mind, there are three major reasons why evolutionary change can happen quickly or very gradually within a population:
1. Population size. In order for change to sweep over the population quickly, it needs to be very small.
2. K or r selected. In a species where offspring are plentiful and reproduce soon after birth (r-selected, i.e. rats), generation times are short, and change can happen rapidly. In a species where individuals invest in small numbers of long-lived offspring (K-selected, i.e. humans), generation times are long, and change happens slowly.
3. Environmental pressure. This is where human evolution is somewhat unique.
SOCIAL VS. BIOLOGICAL EVOLUTION
There is a prevailing idea that humans now evolve socially, rather than biologically. Hopefully at this point in my article I no longer need to argue on the latter clause; we are still evolving biologically. But the former needs addressing. As a species, we use our brains (themselves a product of evolution that began longer ago than we can fathom) to solve problems. Innovations and improvements are passed from generation to generation along with genetic data. The result is that when environmental pressures become intense, a biological coping mechanism is not always necessary.
Social evolution is not constrained in the same ways that biological evolution is, and so it can occur faster and thus more noticeably. With television, radio, and the Internet, an innovation from one corner of the globe can reach billions of people at an unprecedented speed. However, humans are not the only animals that can evolve socially. Other apes are capable of innovation and teaching, as are elephants, dolphins, and who knows what else. Social evolution can reduce the significance of biological evolution, but it cannot cause it to cease.
Mudskippers at the NY Aquarium. Photos by me.
image source: 