How Earth’s biggest animal started small

Far bigger than any dinosaur, the blue whale is the largest known animal to have ever lived.

An adult blue whale can grow to a massive 30m long and weigh more than 180,000kg - that’s about the same as 40 elephants, 30 Tyrannosaurus Rex or 2,670 average-sized men.

But this giant among giants started as something far smaller.

Although the blue whale is an endangered species, its population is on the rise.

Like all whales, the blue whale (Balaenoptera musculus) evolved from a four-legged mammal that lived on land some 48 million years ago. This ancient ancestor, Pakicetus, was only 1.8m long. It foraged in streams and some of its descendants became adapted to living in water. This eventually led to a completely aquatic creature called Dorudon ("Spear-Tooth"), which lived 37 million years ago and grew 4.5m long.

In Dorudon, we see the beginnings of what makes whales so special. Its nostrils moved back from its snout to the top of its head, its forelimbs became stiff flippers, its body elongated, its hind limbs became virtually non-existent and its tail evolved into two rubbery flukes, which propelled the animal forward through the water with an up and down motion, rather than the side-to-side movement of a fish tail.

The evolution from Dorudon to blue whale involved a number of changes to cope with its enormous size. Here are nine you need to know about:

1. Deep breath!

Blue whales can dive for up to an hour at a time, going to a depth of 100m, so they need highly efficient lungs to survive. Two enormous blowholes, big enough for a small child to crawl into, allow the fast and efficient exchange of oxygen. Blue whales exchange between 80 and 90 per cent of oxygen in their lungs each time they breathe, compared to just 10 or 15 per cent in humans. 

2. Can you hear my heart beating?

Oxygen is pumped around its enormous body by an equally massive, four-chambered heart. Weighing some 900kg – and the size of a Mini car – the blue whale’s heart beats once every 10 seconds, pumping 220 litres of blood through its body, and beats so loudly it can be heard from 3km away through sonar equipment.

3. Skin deep

A blue whale’s skin markings are unique, much like fingerprints. The pale bluish-grey colour gives the species its name, although the skin can also look silvery grey or tan, depending on the light. A blue whale has between 80 and 100 long grooves running along the length of its throat and chest.

A blue whale’s skin markings are unique, much like fingerprints.

4. No time (or capacity for tears)

Blue whales have relatively small eyes for their body size – each about the size of a grapefruit – and their eyesight is thought to be weak. They have no tear glands or eyelashes.

5. Sound you out

Despite having no external ears, blue whales are believed to have excellent hearing, using air sinuses and bones to detect sound. They communicate using low-frequency whistles or rumbling noises which can travel hundreds of kilometers and reach 188 decibels – louder than a passenger jet.

6. Big mouth

Their gigantic mouths – big enough to house 100 people – can capture enormous quantities of prey with each gulp of water, filtering the nutritious krill from the expelled water with stiff bristles that grow from the roof of the mouth. During the summer months, they eat up to 6,000kg of krill a day. 

7. Turning up the heat

Blue whales reach sexual maturity between five and 10 years of age. They seek warmer equatorial waters before embarking on an elaborate mating ritual that involves the male and female rolling over one another, diving in a deep dive, then suddenly swimming to the surface for copulating. The males have the biggest penis in the animal kingdom, about 30cm in diameter when erect and 3m in length.

8. Thirsty babies

Blue whales are placental mammals and the foetus develops in the uterus of the mother. The developing foetus grows quickly and after seven months, it is about 3.5m long. The calf is born tail first at 12 months and weighs about 2,700kg, swimming immediately to the surface for air. It suckles on its mother’s two nipples, feeding on up to 180 litres of fat-rich milk a day, allowing it to grow at a daily rate of 90kg. Weaning occurs at around seven or nine months, when the calf is some 15m long.

9. Population counts

It is thought that there were once more than 250,000 blue whales. Now it is estimated there are between 10,000 and 25,000 left in the world. After decades of being hunted for their meat, oil, and other valuable body parts, they are now classified as an endangered species on the IUCN’s Red List.

Source - BBC Earth

Raising eyebrows: how evolution gave us expressive faces

Modern humans might never have raised a quizzical eyebrow had Homo sapiens not lost the thick, bony brows of its ancient ancestors in favour of smoother facial features, a new study suggests.

Researchers at the University of York believe early humans bore prominent brow ridges as a mark of physical dominance, and as the human face evolved to become smaller and flatter, it became a canvas on which the eyebrows could portray a much richer range of emotions. The team stress their conclusions are speculative, but if they are right, the evolution of smaller, flatter faces may have unleashed the social power of the eyebrow, allowing humans to communicate at a distance in more complex and nuanced ways.

We traded dominance or aggression for a wider palette of expression. As the face became smaller and the forehead flattened, the muscles in the face could move the eyebrows up and down and we could express all these subtler feelings. We moved from a position where we wanted to compete, where looking more intimidating was an advantage, to one where it was better to get on with people, to recognize each other from afar with an eyebrow flash, and to sympathize and so on..

The scientists set out to investigate why ancient humans had such prominent brow ridges in the first place. Over the years, researchers have put forward a range of hypotheses. One idea states that the ridge simply filled the gap that would otherwise exist between the protruding face and the braincase. Another argues that a prominent brow served as structural reinforcement, ensuring the face could take the stress of powerful chewing.

The researchers obtained a 3D x-ray scan of an ancient skull belonging to a human ancestor called Homo heidelbergensis that lived in what is now Zambia between 300,000 and 125,000 years ago. Known as Kabwe 1, the skull displayed a thick brow ridge that was even more prominent than the ones seen on Neanderthals.

A computer generated model of a modern skull next to the heavy-browed skull of ancient hominin Kabwe 1

Using computer models, the scientists performed a series of experiments on the virtual skull. First, they looked at how much brow bone was needed if its purpose was to plug the gap between the face and the braincase. Next, the researchers looked at how the stress of chewing spread over the face with and without the brow ridge. They all seemed to make little difference. What was left was the plausibility of a social explanation.

It is unclear what factors led the human face to become smaller over time and lose its thick brow ridges, but a flatter face may have paved the way for richer human communication and with that the greater collaboration that emerged with the rise of Homo sapiens. In Homo heidelbergensis and other ancestors, the thick brow signified physical strength at the apparent expense of eyebrow gymnastics: in those early humans, the muscles that moved the eyebrows simply pulled them back and forth over their brows.

While one evolutionary psychologist wonders why other primates do not use them more... given the importance of eyebrows in human communication. It is plausible to suggest that it has something to do with increased need for more complex communication in the larger social groups that evolved late during the course of human evolution.

Yet another researcher believes that the human face has many more muscles which are likely to have contributed substantially to the development of socially sophisticated communication, group cohesiveness and functioning, and therefore survival and progress.

Sources -

1. The Guardian - Science
2. Nature Ecology & Evolution