The theory of evolution is the best biological framework that explains how all life on the planet got to where it is today. It has not be proven wrong once, but that doesn’t mean it’s perfect. In the past decade alone, accelerated by the immense progress made in genomic sequencing and big data analysis, scientists have come to understand that there’s more depth to evolution. As such, some are suggesting the Theory of Evolution should be updated.
Earlier this month, some of the top biologists in the field met in London for an event hosted by The Royal Society. The main subject of the evening were recent developments in biology that “have produced calls for revision of the standard theory of evolution.”
Wait a minute. Does that mean there’s something wrong with the theory of evolution? Not at all. It’s just that, in light of what we now know about what drives evolution and the biological evolutionary mechanisms, we can come up with a better definition of evolution.
The theory of evolution is the brainchild of Charles Darwin’s Theory of Natural Selection and Gregor Mendel’s Mendelian Inheritance, which underpins classic genetics. Natural Selection leads to evolutionary change when individuals with certain characteristics have a greater survival or reproductive rate than other individuals in a population and pass on these inheritable genetic characteristics to their offspring.
During his time, however, Darwin was not aware of genes and genetic drift. This is where Mendelian Inheritance comes in, which recognizes that characteristics are inherited as discrete entities called genes and that random genetic drift may be as important as natural selection itself.
When the two landmark theories are combined, you get the modern evolutionary synthesis which basically postulates that speciation is (usually) due to the gradual accumulation of small genetic changes. In other words, macroevolution is simply a lot of microevolution.
Since it was first proposed in the 1940s, the modern synthesis has been the go-to model for the theory of evolution. But a lot has happened since, and the modern synthesis might be in for an overhaul.
At the event in London, Eva Jablonka, a biologist at Tel Aviv University, argues that a complete, contemporary theory of evolution needs to take account the notion of heredity absent genes. What Jablonka was referring to was ‘epigenetics’ — heritable changes in gene expression. For instance, while there are thousands of genes coded by our DNA, not all are active. Genes are regularly switched ‘on’ or ‘off’ during our lifetimes through chemical changes called methylation. This can happen for a lot of reasons, and it all depends on the environment. For instance, smoking modifies 7,000 genes.
When the cell divides, the methylation is present in the new cell as well. Moreover, changes in genes that were active early in life, but switched off later in adulthood, can be transmitted to offspring in certain cases.
One textbook example is the case of the Dutch Hunger Winter, which lasted from the start of November 1944 to the late spring of 1945. During this time, West Holland was still under German control. A German blockade resulted in a catastrophic drop in the availability of food to the Dutch population. At one point the population was trying to survive on only about 30 percent of the normal daily calorie intake. They ate anything they could get their hands on; grass, tulip bulbs, book covers. By the time Holland was liberated in May 1945, some 20,000 people had died of starvation.
Mothers well fed around the time of conception, but malnourished only for the last few months of pregnancy gave birth to smaller babies, on average. On the other hand, mothers who were malnourished for the first three months of pregnancy, but were then well fed (the blockade was lifted) were likely to birth normal-size babies. The fetus “caught up” in body weight, so to speak. That’s pretty straightforward so far, but in the course of decades, doctors they found those who were born small stayed small all their lives, with lower obesity rates than the general population, despite having access to as much food as they wanted. That’s not all. The children of the mothers who had been malnourished only early in their pregnancies had higher obesity rates than normal. Then, some of the same effects were observed, to a lesser degree, in the children of those who had been born in those troubled time, that is to say, the grandchildren of the malnourished mothers.
Remarkably, Holocaust survivors also passed down stress to their offspring.
Epigenetics does not contradict Natural Selection. Carl Zimmer quotes Jablonka for Quanta as saying “epigenetic differences could determine which organisms survived long enough to reproduce.”
Another factor that’s not included in modern synthesis but seems to drive evolution is the so-called ‘plasticity’. It’s plasticity that helps explain the weird but startling diversity in Homo fossils. These fossils include the remains of our ancestors who lived 1.5 to 2.2 million years ago. Most can be pinpointed to the same species, but in some cases you get some fragments that look like they come from two separate species. Some were tall, others short. Some have big brains, some have smaller brains, despite being essentially the same species.
At a meeting in London, Susan Antón, a paleoanthropologist at New York University, argued that Africa’s went through periods of wild and dramatic swings. She says that this plasticity is highly responsive and time sensitive. For instance, the quality of food a pregnant woman eats can influence the size and health of the baby, and this influence can last well into adulthood.
Then there’s the case of the advent of farming some 13,000 years ago. When viewed through an evolutionary lens, persistent behaviors have to be explained by means of selection. For instance, we’re still farming because it gave us an evolutionary edge as it increased the available food resources. That’s pretty straightforward but the first human farmers had to go through a lot of pain and, likely, a negative return of investment. The first crops were woefully inadequate since they were not yet adapted. Just look at what fruits and veggies used to look like before we domesticated them.
Melinda Zeder, an archaeologist at the Smithsonian Institution, says there’s no evolutionary advantage per the modern synthesis that can explain this seemingly masochistic resilience to keep experimenting with crops. “You don’t get the immediate gratification of grabbing some food and putting it in your mouth,” Zeder told Zimmer, who was presented at the event in London.
“Zeder argues that there’s a better way of thinking about this transition. Humans are not passive zombies trying to survive in a fixed environment. They are creative thinkers who can change the environment itself. And in the process, they can steer evolution in a new direction. Scientists call this process niche construction, and many species do it. The classic case is a beaver. It cuts down trees and makes a dam, creating a pond. In this new environment, some species of plants and animals will do better than others. And they will adapt to their environment in new ways. That’s true not just for the plants and animals that live around a beaver pond, but for the beaver itself,” Zimmer wrote.
The extended evolutionary synthesis, as described in the Proceedings of the Royal Society B, attempts to include these new trains of thought into the theory of evolution. Critics abound so many other such meetings will likely have to be held before the theory of evolution can itself stand by its own definition: adapt, respond, pass on — evolve.