Evolution process

How does evolution occur?

Individuals in populations possess a variety of characteristics that are a result of the interaction between their genes and the environment. Differences in the characteristics of the population come about due to both genetic and environmental sources of variation, with mutations being the ultimate source of all genetic variation.

Because each individual possesses slightly different traits, it follows that each individual has a slightly different level of fitness relative to the environment.

Fig. 1 - Arctic fox blending in with its habitat

Evolution acts upon this variation in observable traits. Different evolutionary processes, such as natural selection, sexual selection, and genetic drift, act upon the variation in the population, resulting in some traits becoming more common and others more infrequent.

As a result, over time, populations become fitter and better suited to their environment. As populations become more and more specialised for their specific environments, they might become distinct species that can no longer interbreed with one another in a process known as speciation.

DNA → Mutations → Change in genotype → Changes in phenotype → Variability in populations (adaptations) → Changes in allele frequency in the gene pool → New species → either evolution (continued success in the environment) or extinction (overwhelmed by environmental pressures)

Who is the father of evolution?

The theory of evolution by natural selection is largely credited to Charles Darwin. He discussed it in his book "On The Origin of Species", although it was also conceived independently by Alfred Russel Wallace.

Darwin based this theory on several observations:

• Firstly, observable traits such as morphology, physiology, and behaviour vary among individuals. In other words, there is phenotypic variation within populations.

• These varying traits confer differential fitness, which means they lead to different levels of success in terms of survival and reproduction.

• Finally, traits are heritable, which means that they are passed down from parent to offspring.

Darwin argued that members of a population are more likely to be replaced by offspring of parents who have favourable traits and are better able to survive and reproduce. As time goes on, populations gradually change to become better suited to their environments.

What is the evidence for evolution?

There is overwhelming evidence that the theory of evolution is true. Let’s go over a few examples:

The genetic code

Firstly, the structure of the genetic code is very similar for all organisms on earth. Our DNA is composed of the same nitrogenous bases - A, C, T and G - and we share a significant proportion of our DNA with our closest taxonomic relatives. The closer one species is to another, the more similar their genetic information tends to be.

The fossil record

Next, we have an extensive fossil record of the organisms that used to live on Earth but have gone extinct. By studying fossils, we have been able to infer what life used to look like on Earth and understand more about how life evolved and diversified. Of course, the fossil record is not complete. The way fossils are formed means that soft-bodied organisms may not be accurately represented in our records. There are also many intermediate forms between kinds of organisms that we have not discovered yet or that were not fossilised at all.

Selective breeding

There are also many examples of plants and animals whose evolution has been guided by humans through selective breeding, including dogs, domesticated farm animals, and agricultural crops. Darwin used selective breeding as strong evidence for evolution - in this case, through artificial selection, when he first introduced his theory to the public.

Real-time evolution

Finally, we can observe evolution happening in real-time. For example, fast-evolving organisms such as bacteria continue to evolve and adapt to the antibiotics we use against them. There are now many strains of ‘superbug’ that have adapted to resist antimicrobial compounds and will be able to survive heavy doses of medicine.

What are the types of evolution?

There are several terms used to describe patterns in which the process of evolution occurs in different organisms. Examples of these include:

• Divergent evolution

• Convergent evolution

• Parallel evolution

Fig. 2 - Different types of evolution

What is divergent evolution?

Divergent evolution refers to the process by which groups descended from the same common ancestor accumulate genetic differences, which ultimately leads to speciation. This might occur as a response to changes in the environments of the two groups, such as changes in the abiotic conditions or the introduction of new biotic interactions.

What is convergent evolution?

Convergent evolution is the process by which groups that are not closely related - that is, they are not descended from the same direct ancestors - independently evolve similar features in response to similar selection pressures. In other words, through convergent evolution, different groups separately arrive at the same solution to similar problems. For instance, birds, flying insects, and flying mammals have all arrived at the convergent phenotype of wings as a ‘solution’ to the ‘problem’ of mobility. There is no one close common ancestor for all of these winged animals. Indeed, the anatomy of wings looks very different from group to group; however, most wings operate based on the same principles due to flight physics.

What is parallel evolution?

Parallel evolution refers to the process by which two groups sharing a similar trait, evolve another trait in a similar environment.

To understand how this might occur, let’s imagine two groups of similar plants that are in different locations but are exposed to very similar environmental conditions. Because they are dealing with the same conditions, they might evolve similar adaptations completely independently from one another. For instance, if they were in an arid environment, they might develop a waxy cuticle and stems that can store water.

Parallel evolution is often confused with convergent evolution. The important thing to keep in mind here is that in convergent evolution, two groups arrive at the same phenotype from different starting points, while in parallel evolution both groups come from similar starting points.