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Thoroughbred horses are possibly the most genetically optimized animals aside…

Brief

Thoroughbred horses have been intensively shaped by centuries of selective breeding—recorded in the General Stud Book since 1791—producing extreme traits like Secretariat’s 10 kg heart. The Darley Arabian (imported 1704) appears in roughly 95% of pedigrees, while historical selection (Bronze Age spotting, medieval 14‑hand warhorses) reveals tradeoffs and costs.

Why it matters

Thoroughbred horses are possibly the most genetically optimized animals aside from broiler chickens; Secretariat’s heart weighed 10 kg, about twice a regular horse's heart.

Key details

  • Breeders have recorded thoroughbred ancestry in the General Stud Book since 1791; the Arabian stallion Darley Arabian was imported to England in 1704 and is an ancestor of about 95% of modern thoroughbreds.
  • Selective breeding targeted traits like stronger backs, lower anxiety, and shorter generations; Bronze Age breeding for leopard spotting produced night blindness, and medieval warhorses averaged ~14 hands high (pony-sized).
Source evidence

With the possible exception of broiler chickens, no creature has been so genetically optimized as the thoroughbred horse.

Read more about how we made the ultimate race horse today in Works in Progress: worksinprogress.co/issue/the…

🐎 Secretariat, the greatest racehorse of all time, had a heart that weighed 10kg, twice the size of a regular horse's.

🐎 We have been consistently recording the ancestry of thoroughbreds in the General Stud Book since 1791.

🐎 Breeders discovered that horses from Arabia, Central Asia and North Africa were often faster. So the Genghis Khan of thoroughbred horses is an Arabian stallion called the Darley Arabian, brought to England in 1704. He’s an ancestor of 95% of all modern thoroughbreds.

🐎 The first records of horse domestication show us selecting for stronger backs, lower anxiety and shorter generations.

🐎 In the Bronze Age, people bred horses for leopard spotting, which incidentally, caused night blindness.

🐎 Medieval warhorses were much smaller than today’s massive beasts. They stood at about 14 hands high, roughly the size of a pony.

Link

The ultimate horse - Works in Progress Magazine

Selective breeding has pushed horses to the limits of biology. But at what cost?
worksinprogress.co