An adaptation, or adaptive trait, is a feature produced by DNA or the interaction of the epigenome with the environment. While not all adaptations are totally positive, for an adaptation to persist in a population it must increase fitness or reproductive success. All offspring, whether formed sexually or asexually, inherit their traits from their parents. In asexual reproduction mostly identical clones are created.
Adaptation arises in asexual populations through mutations in the DNA, errors copying the DNA, or the interaction of the DNA with changes in the environment. In sexually reproducing populations, adaptation arises through similar mechanisms with the added effects of recombination during meiosis, and a more complex DNA molecule. An adaptation can become vestigial, or unused, when changes in the population or environment render it useless. An adaptation also has certain trade-offs, such as the energy it takes to create an adaptation or the increase in predation an adaptation may cause.
Types of Adaptation
Genetic Mutation and Recombination
Deoxyribonucleic acid, or DNA, is the molecule that carries the information necessary for creating and maintaining life. DNA is made from a series of nucleotides, 4 small chemicals which chain together. The sequence of these chemicals can be read by specialized enzymes and organelles within cells to produce new proteins. These proteins have various functions, and determine how the cell functions within its environment.
Since the first proteins and cellular constituents aggregated to form the first self-replicating cell, the interaction between DNA and the environment has driven adaptation. Single-celled organisms rely solely on molecular adaptation, since their basic structure prohibits the complex nature of developing new limbs other structures. Instead, an adaptation in a prokaryote comes from advantageous mutations within their DNA which create new proteins or alter the effects of current proteins. The chemical reactions enabled by these proteins allow the organisms to more efficiently collect nutrients, grow, and divide. The adaptation will persist in the population as long as it increases fitness and reproduction.
In eukaryotes and multi-cellular species, the process of mutation also drives adaptation. As in prokaryotes, the DNA is controlled by a system of proteins which interacts with the environment, known as the epigenome. In eukaryotes, the complexity of this system has increased. An adaptation can affect the organism on any level, from creating a different way to replicate DNA to developing entirely new organelles and structures of the body. Studies have shown that mutations are often deleterious, or do not adapt the organism to the environment. These mutations are not typically considered adaptations because they do not persist in the population at high levels. However, as the environment changes mal-adapted traits may become beneficial and persist as an adaptation to a new scenario.
Changes in Environment
Changes in the environment are second major category of adaptation. In many cases the epigenome is as or more important that the DNA itself. Large environmental changes, such as a change in ocean temperature or acidity, can affect a great number of species. As the environment changes, the proteins of the organisms start to function differently. Changes to the DNA or to how the epigenome interacts with the new environment can lead to a novel adaptation. For instance, life on Earth currently depends on a system of oxygen and carbon dioxide, which its organisms use for energy and respiration. Scientists have estimated that this environment was not present until photosynthetic organisms started creating oxygen and depositing it into the atmosphere. The new chemicals in the atmosphere started a wave of adaptation which has led to the current biome we have now.
As more and more species became differentiated, their interactions with each other started to drive adaptation as much as the simple composition of the atmosphere. Vast food webs developed and fell apart over the billions of years of life. These events were driven in part by the ability of organisms to quickly form an adaptation to a situation and continue reproducing. However, during many of these events, as many as 90 percent of species didn’t survive the abrupt change. While adaptation can make organisms more competitive in an environment, it can also make them less flexible to survive in a changing environment.
The complex interactions between animals have also led to diverse forms of selection which affect and form adaptation among the organisms involved. In sexual selection, for instance, differences and adaptation strategies between genders are not necessarily determined by the environment, but simply by the strange selection preferences of individuals trying to reproduce. Many birds show highly colored males, selected for by the dull colored females. The adaptation of color in the males is a characteristic used to attract more females. The females’ adaptation of dull color, on the other hand, is the result of a more directional selection of the predator prey relationship. Less colorful females are less likely to be spotted by predators. While these two adaptive traits contradict each other, they have persisted because they benefit the males and females in different ways.
Examples of Adaptation
If you’ve ever seen a Rhinoceros Beetle, you’ve probably wondered what it uses those huge horns for. Seen below is a male Rhino Beetle, with its distinctive headgear.
Like all arthropods, the beetle is divided into segments. These various sections are very responsive to adaptation. In the Rhino Beetle, the head section has developed these large thorns. The male beetles use these large obtrusions to fight each other, in competition for females. It is presumed that ancestral beetles had little to no horns. As the beetles competed for mates over many generations, mutations which created a better way to peel the opponent off his feet were rewarded. Over time, this adaptation of large horns emerged. Horns with the greatest ability of defeating opponents allow those males to reproduce more and the adaptation will persist within the population.
Digestive Tract in Mammals
If you were to dissect various mammals, you would find something very peculiar in the size and composition of their digestive tract. Carnivores, like wolves and cats, have very short and simple digestive tracts. In fact, the more carnivorous an animal, the shorter and simpler the digestive tract is. Meat and animal products are easily digested. The adaptation of a short gut allows these animals to quickly process the energy out of their meaty meal, before it starts to rot in their gut.
Herbivores, on the other hand, have a long and complex digestive system. Some mammals, the ruminants, have multiple stomachs to process the energy out of grasses and other tough plants. Non-ruminant herbivores have complex twists and turns in their guts which increases the surface area and the amount of time food spends in the digestive tract. This adaptation allows the animals to process all of the energy out of the plant material. Interestingly, humans have a vastly complex gut, an adaptation for herbivores. Part of the complex story behind diet, nutrition, and health probably arises from the fact that the Western diet focuses on meat, rather than the foods our body has adapted to eat.