Question

How does phylogeny help in building broad historical sequence of biological evolution? Explain with the help of the example of horse.

Answer 1

Phylogeny helps in building a broad historical sequence of biological evolution by tracing the evolutionary relationships and changes that have occurred over time, based on anatomical, fossil, and genetic evidence. Through phylogenetic studies, scientists can arrange organisms and their ancestors in a sequence that reflects the order in which they evolved.

Using the example of the horse:

1. Fossil records of the horse show a clear historical sequence of evolutionary changes over about 60 million years.
2. The earliest ancestor, Eohippus (lower Eocene), was small (about 30 cm tall) and had four digits on the forelimbs and three on the hind limbs.
3. Later forms like Mesohippus (Oligocene) showed a reduction in the number of digits: three digits on each leg, with the middle one mainly supporting the body.
4. In the Miocene epoch, Merychippus was larger (about 100 cm), still with three digits on each leg, but only the middle digit touched the ground.
5. Finally, the modern horse, Equus (Pleistocene), evolved with a single functional digit on each limb, longer limbs, an elongated head and neck, and teeth adapted from browsing to grazing.
6. These evolutionary adaptations correspond to environmental changes, from dense forests to open grasslands, showing how the horse’s structure changed to suit its habitat.
7. Thus, phylogeny reveals the sequence of changes, from a small multi-toed ancestor to a large, single-toed modern horse, illustrating both anatomical and environmental evolution.