Humans are members of the great ape family Hominidae, and the physical similarities between us and our primate cousins are clear. We have the same arrangement of internal organs and roughly the same number of bones, we lack external tails, and we even get the same diseases. So it only makes sense that we share some psychological similarities as well. A 2012 study published in the Proceedings of the National Academy of Sciences reported that chimpanzees and orangutans experienced a midlife crisis similar to that of humans.

Humans and apes have the same blood type.

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Like humans, other great apes have A, B, AB, and/or O type blood, all thanks to common ancestors who lived nearly 20 million years ago. However, humans can’t donate blood to chimps (or vice versa) any time soon, as subtle blood differences make such an idea a dangerous one.

The study analyzed the behavior of 508 chimps and orangutans in captivity at zoos in five different countries, and found that these animals’ well-being hits its nadir around their mid-20s or early 30s (the equivalent of middle age for chimps and orangutans). Of course, scientists couldn’t directly ask the chimpanzees how they felt, but instead relied on zookeeper questionnaires to assess the animals’ overall mood, level of joy in social situations, and how successful they were in achieving particular goals. Although the dataset is subjective, its sheer size highlights an overall trend that’s remarkably human, since we also tend to experience a dip in happiness and well-being around midlife. It’s just another trait that entwines us with our primate brethren. 

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Snakes are often pictured curled around a tree in a dense jungle or hiding in a desert waiting to strike some unsuspecting prey. But they’re just as capable in the water as they are on land — in fact, all species of snakes can swim. In North America, a famous example is the cottonmouth (Agkistrodon piscivorus), named for the white color on its mouth that goes on full display when the creature is angry. This snake, native to the southeastern U.S., also goes by the name “water moccasin” because of its predilection for estuaries, bays, and rivers. 

All snakes lay eggs.

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Only about 70% of snakes are oviparous, meaning they lay eggs to produce young. The other 30% give birth, known as ovoviviparity, to snakes encased in an amniotic sac. This is especially true for snakes in cold climates, where eggs wouldn’t survive.

But even going a step beyond the familiar cottonmouth, some 60 species of marine snakes derived from the cobra family call the ocean their home, and monstrously large snakes such as anacondas also spend most of their life in the water. Even snakes that generally have no business in water, such as the desert-loving rattlesnake, can swim in a pinch. Members of the suborder Serpentes (to which all snakes belong) are such good swimmers because their elongated bodies can easily propel them through the water, and some have even evolved tails that look like paddles. But don’t worry, ophidiophobes: It’s not like the Earth’s waters are teeming with snakes. Snakes can’t live in areas that are too cold, and many spots — Alaska, New Zealand, and Ireland, to name a few — are entirely free of them. 

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Kangaroos are one of several biologically unique creatures endemic to Australia. One of their most unusual traits is that their long hind feet and muscular tails prevent them from being able to walk backward except with great difficulty. In fact, kangaroos can’t even really walk forward like other animals. Instead, they ambulate using a hopping motion called saltation in which their hind feet touch the ground synchronously instead of alternating one at a time. They also use their long tails to balance and propel themselves forward, almost like a third hind leg. This physiological composition makes it effectively impossible for kangaroos to walk or hop backward, as their tails are far too heavy and cumbersome to allow for easy reverse navigation. When they do want to move “backward,” they do so by turning around and facing that direction.

Kangaroos are only about an inch long when born.

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Baby kangaroos (joeys) are roughly an inch long when born. Immediately after birth, the baby crawls unassisted into the mother’s pouch, where it spends its first four months. After that the joey emerges for short periods of time to graze before leaving the pouch for good after about 10 months.

Much like their marsupial mates, emus, another endemic Australian creature, also struggle to walk backward. While these large, flightless birds are capable of sprinting at speeds of up to 31 mph, they can only do so facing forward. When they do move backward, they’re forced to do so very slowly. It’s believed that their knee joints, in addition to their long legs and unusual body shape, prevent them from moving quickly in reverse. Given this shared difficulty in backing up, it’s worth noting that both the kangaroo and the emu also share the distinction of appearing on Australia’s Commonwealth Coat of Arms. According to the country’s Department of the Prime Minister and Cabinet, the animals were chosen to symbolize a country that’s always moving forward rather than backward.

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