I think humans when the lifespan was 10 may have looked like apes. As the life span increased, their beauty and intelligence increased
From the Cakkavattisutta
** Among the people who live for ten years, there will be an interregnum of swords lasting seven days. During that time they will see each other as beasts. Sharp swords will appear in their hands, with which they’ll take each other’s life, crying, ‘It’s a beast! It’s a beast!’**
And so, mendicants, from not providing money to the penniless, all these things became widespread—poverty, theft, swords, killing, lying, backbiting, sexual misconduct, harsh speech and talking nonsense, desire and ill will, wrong view, illicit desire, immoral greed, and wrong custom, and lack of due respect for mother and father, ascetics and brahmins, and failure to honor the elders in the family. For the sentient beings among whom these things were widespread, their lifespan and beauty declined. Those people who lived for two hundred and fifty years had children who lived for a hundred years.
There will come a time, mendicants, when these people will have children who live for ten years. Among the people who live for ten years, girls will be marriageable at five. The following flavors will disappear: ghee, butter, oil, honey, molasses, and salt. The best kind of food will be finger millet, “Finger millet”
The ten ways of doing skillful deeds will totally disappear, and the ten ways of doing unskillful deeds will explode in popularity. The narrative above traced the gradual disappearance of these ten factors. Those people will not even have the word ‘skillful’, still less anyone who does what is skillful. And anyone who disrespects mother and father, ascetics and brahmins, and fails to honor the elders in the family will be venerated and praised, just as the opposite is venerated and praised today.
There’ll be no recognition of the status of mother, aunts, or wives and partners of tutors and respected people. The world will become dissolute, like goats and sheep, chickens and pigs, and dogs and jackals.
They’ll be full of hostility towards each other, with acute ill will, malevolence, and thoughts of murder. Even a mother will feel like this for her child, and the child for its mother, father for child, child for father, brother for sister, and sister for brother. They’ll be just like a deer hunter when he sees a deer—full of hostility, ill will, malevolence, and thoughts of killing.
Among the people who live for ten years, there will be an interregnum of swords lasting seven days. During that time they will see each other as beasts. Sharp swords will appear in their hands, with which they’ll take each other’s life, crying, ‘It’s a beast! It’s a beast!’
But then some of those beings will think, ‘Let us neither kill nor be killed! Why don’t we hide in thick grass, thick jungle, thick trees, inaccessible riverlands, or rugged mountains and survive on forest roots and fruits?’ “Let us neither kill nor be killed” is an idiomatic phrase, the Golden Rule framed as a negative: “Let us not do unto others nor let others do unto us.” It is explained by the commentary as, “Let us not take even a single person’s life or let them take ours”.So that’s what they do.
When those seven days have passed, having emerged from their hiding places and embraced each other, they will come together and cry in one voice, ‘Fantastic, dear foe, you live! Fantastic, dear foe, you live!’
Then those beings will think, ‘It’s because we undertook unskillful things that we suffered such an extensive loss of our relatives. We’d better do what’s skillful. What skillful thing should we do? Why don’t we refrain from killing living creatures? Having undertaken this skillful thing we’ll live by it.’ The first precept, and the first of the ten ways of skillful action. The Buddhist ethical principles are not just a part of Buddhist teaching, they are essential for the healthy functioning of human society.So that’s what they do. Because of undertaking this skillful thing, their lifespan and beauty will grow. Those people who live for ten years will have children who live for twenty years.
Then those beings will think, ‘Because of undertaking this skillful thing, our lifespan and beauty are growing. Why don’t we do even more skillful things? What skillful thing should we do? Why don’t we refrain from stealing … sexual misconduct … lying … backbiting … harsh speech … and talking nonsense. Why don’t we give up covetousness … ill will … wrong view … three things: illicit desire, immoral greed, and wrong custom. Why don’t we pay due respect to mother and father, ascetics and brahmins, honoring the elders in our families? Having undertaken this skillful thing we’ll live by it.’ So that’s what they do.
Because of undertaking this skillful thing, their lifespan and beauty will grow. Those people who live for twenty years will have children who live for forty years. Those people who live for forty years will have children who live for eighty years, then a hundred and sixty years, three hundred and twenty years, six hundred and forty years, 2,000 years, 4,000 years, 8,000 years, 20,000 years, 40,000 years, and finally 80,000 years. Among the people who live for 80,000 years, girls will be marriageable at five hundred.
Cakkavattisutta
The pali translations are available at SuttaCentral