Domestication of vertebrates

The domestication of vertebrates is the special bond between vertebrate animals like birds and mammals, and the humans who help care for them. This bond has changed both the animals and us over many years.

Charles Darwin studied these changes. He noticed that some traits make domesticated animals different from wild animals. Humans can choose which animals have babies to get the best traits, called selective breeding. Animals can also change on their own because of natural selection. These changes are written in the animals' genes.

Not all animals can be domesticated. They need to get along with humans, have babies easily, and adapt to new places and foods. Most animals became domestic in three ways: by living close to humans, being raised for food, or being used for work. The dog was the first animal to be domesticated, appearing in Eurasia long before farming began. Other common pets today are cats and more dogs.

Definitions

Domestication is when humans and animals live and work together over many years. Humans help animals by giving them food and care. This helps make sure there are enough animals for people to use.

Both humans and animals gain from this partnership. Domestication can change animals. They may become gentler, change colors, have smaller teeth, or have floppy ears. These changes make animals fit better with human life. Domestication is not the same as just taming an animal. Taming means an animal gets used to people, but domestication means the animal’s family traits change over many generations to live better with humans. Some animals can be tamed but are not fully domesticated.

History, cause and timing

Further information: History of agriculture

The domestication of animals and plants began because of big changes in the climate after the Last Glacial Maximum around 21,000 years ago. These changes made it harder for people to find food, so they started to take care of animals and grow plants. The first animal to be domesticated was the domestic dog, which came from wolves at least 15,000 years ago.

As time went on, people in many places began to farm more. This led to bigger towns and more people. In places like the Fertile Crescent, goats, pigs, sheep, and cattle were among the first animals to be tamed. Over thousands of years, many more animals, like horses and chickens, were also brought closer to humans.

Universal features

Wild animals are getting smaller compared to animals that people keep as pets or on farms. In fact, all the farm cows together weigh more than every wild mammal in the world. Domestication is an ongoing process, so it keeps changing animals in new ways.

Some animals are easier to domesticate than others. They might be friendly, easy to care for, and not scared by new things or people. For example, zebras have not been domesticated because they are too wild and nervous around humans. Scientists have studied why only some animals can be domesticated. They found that successful domesticated animals usually have traits like eating simple food, growing quickly, breeding in captivity, having friendly temperaments, staying calm, and living in social groups.

When animals are domesticated, their brains often change too. Studies with foxes showed that when they were bred to be friendly, their brains became smaller over time. This change affects parts of the brain that control how scared or aggressive an animal might be. Domestic animals often have other traits in common too, like floppy ears or spots on their fur, which may be linked to the same genes that make them friendly. Even when these animals escape and live without humans for many years, they usually don’t go back to having the larger brains of their wild ancestors.

Categories

Domestication is the last step in the relationship between animals and humans. It has several levels. Scientists have five main categories for animal domestication: wild, captive wild, domestic, cross-breads, and feral.

Wild animals live in nature and change through natural selection. Captive wild animals are kept by humans, which changes their natural selection. Domestic animals are raised by humans, who pick traits they like. Cross-breed animals are mixes of wild and domestic animals, and can look like either parent or something new. Feral animals were once domestic but went back to the wild.

A study in 2015 looked at pigs and found differences in their teeth between wild, captive wild, domestic, and hybrid groups. This helped support these categories. More research is needed on feral pigs and their genetics.

Main article: allometry

Pathways

Since 2012, scientists have agreed on a model that explains how animals became domestic pets and helpers. There are three main ways this happened.

The first way is called the commensal pathway. Animals like dogs and cats followed this path. They lived near humans because they could eat food left by humans or hunt small animals near human camps. Over time, the friendliest animals became closer to humans, leading to a closer bond. This process started over 15,000 years ago with wolves becoming dogs.

The second way is the prey pathway. Animals like sheep and cows were once hunted for food. Humans began managing these animals more carefully, controlling where they went and ate, which led to domestication. This happened in areas like the Fertile Crescent around 11,700 years ago.

The third way is the directed pathway. Humans deliberately brought animals like horses into their world for work, such as transportation. This required more effort because these animals were not naturally suited to living close to humans.

Post-domestication gene flow

When people moved to new places with their pets and farm animals, they sometimes met wild animals that looked similar. These animals could have babies together because they were closely related. Over time, this mixing changed the genes of the pets and farm animals.

We can now study genes more easily. This shows that animals often mix genes with wild ones, even if they are far away or not usually farmed. For example, many chickens today have genes from wild birds in South Asia, and African cows have mixed genes from European and Asian ancestors. This mixing still happens today, such as with reindeer. Because of this, it is sometimes hard to know exactly where and when some animals were first tamed by humans.

Main article: Post-domestication gene flow
Main articles: Domestication and Selective breeding
Further information: Hybrid (biology))

Positive selection

Charles Darwin noticed some important traits that make domestic animals different from their wild ancestors. He explained the difference between humans choosing animals with special traits and natural changes that happen on their own.

Domestic animals often have special features like different fur colors, floppy ears, and smaller brains. Experiments with silver foxes showed that picking animals that are friendly can lead to many other changes in just a few generations. This shows that even without planning, choosing friendly animals can create domestic traits. We see similar results in deer, mink, and quail. Studies of genes have found many linked to fur color changes and other traits. Research on pigs shows they were domesticated in different places and mixed with wild boars, but humans still chose traits that made them easier to care for. Unlike other animals chosen for food or work, dogs were first chosen for their behavior. Studies found a small number of genes that changed how dogs act, making them less fearful and more friendly compared to wolves.