People with stiff thumbs will be self-willed people. There was a person whose thumb was supple. He used to bend his thumb backwards until the tip of the nail touched his wrist. He was one absolutely devoid of anything resembling a will. Every part of the body, including the nails or hair signifies something of a man's character. Prominent cheek bones indicates independent decisions not easily influenced by others. A squint means unreliability. So also a crooked neck. Bushy eyebrows stand for intense analysis in the mind. Horizontal lines in the forehead show achievement. A vertical line in the middle of the forehead known as the 'suspended needle' indicates one's rising in power. Palmistry and physiognomy are a wide sastra. They are the aspects of swarupa expressing swabhava.
These sastras were not written by external mental observation that collects data and organises it statistically. When the subtle vision in a Rishi opens, he 'sees' the whole sastra and codifies it. Such a subtle vision can be spiritual or mental or below the mental - the vital. Before mind was born in the world in the period of the Upanishads, all civilizations were SUBTLE of various levels. The Rishi's dark complexion grew fair when the light was born inside. Sri Aurobindo's body acquired a golden tint when the Supramental Golden Light took birth in him. After He attained Samadhi on Dec. 5, 1950, the Golden Light of the Supramental world descended into his very body and stayed there for three days. When the inner swabhava changes out of education or yoga, the external lines disappear or lines that were not there appear.
A stiff thumb can grow flexible when the man loses something of his obstinacy. A soft thumb can grow stiff as the non-existent will takes shape inside. Our tradition says swabhava cannot change. Sri Aurobindo says when someone surrenders his swabhava to the inner Divine, it begins to transform itself into the Divine Swabhava. Even there, Sri Aurobindo cautions that one should work to get the better of swabhava along the lines of it, not against it. Sri Aurobindo's yoga is called Integral Yoga or Purna Yoga. It is known as the yoga of Transformation. The best description of His yoga is the Yoga of Self-Perfection.