Life on Earth has spent the last 3.7 billion years growing, changing and evolving in response to the changing environment, so it seems likely that there might be some evolutionary leftovers picked up along the way. Vestigial structures are typically organs, tissue or bones that once served a purpose for our ancestors. However, over time their usefulness has waned, such as hind leg bones in whales or wings among flightless birds.
It’s largely accepted that an organ or structure that appears to lack a certain function in at least two other closely related species is deemed vestigial. These vestiges aren’t always anatomical; they can also be genetic or behavioural. For example, when a baby is born their tiny hands and feet can quickly and robustly grip objects. This is known as the palmar reflex and is thought to be the instinctual leftovers