Modern horses have an incredibly diverse maternal DNA but, in terms of paternal DNA, the situation is pretty basic. This poor variability seems to be the direct result of selective breeding practices that were common about 3,000 years ago. During the Iron Age, the practice was necessary since the male-female rates among horses were unequal.
Modern horses have a poor paternal DNA diversity
When humans first started domesticating horses, they had to deal with a great imbalance between the number of males and the number of females. This called for a series of selective breeding techniques, as they needed to overcome this shortage. The practices had a big impact on modern horses as follows.
Nowadays, researchers have noticed a great diversity in the mitochondrial DNA horses inherit on their maternal lineage. However, in terms of paternal DNA, this diversity is relatively low. This is quite interesting, since the diversity of the Y chromosome appeared bigger in the past.
Therefore, they started questioning this situation, and decided to find out what happened. For this, they studied 16 Y chromosomes coming from 96 types of stallion DNA that come from different periods. The oldest ones date back 5,000 years ago, when people had first started domesticating horses.
Selective breeding influenced the future horse populations
This poor paternal diversity appeared for the first time 3,500 years ago. This was close to the beginning of the Iron Age, when the first people started using selective breeding among horses. Therefore, by choosing to ignore certain stallions during breeding, they restricted the DNA the future generations of horses inherited.
Selective breeding actually produced new horse populations that had more stallions. This convinced the Romans to change their techniques again. Instead of focusing on females, they selected a few males as the main agents of breeding. This produced a few strong lineages of stallions, while others remained poorer.
The study was published in the journal Science Advances.
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