Evolution of eyes

Eyes are all over the animal kingdom but no 2 pairs of eyes operate in the same manner. They evolved numerous times in different lineages and is a great example of divergent evolution. 600 million years ago, ocean life is simple. The ancestors of jellyfish have light sensitive organs called eye spots. Today jellyfish are able to use their eye spots to avoid predators and find food.

544 million years ago, the animals became faster and more plentiful.  Compound eyes appeared on trilobites and gave them a supreme survival advantage for 300 million years. Insects are modern day related predecessors of animals like trilobites. Insects have multiple lenses in their compound eyes. Dragon flies have 29,000 lenses in each of their eyes and they can capture images 5 times faster than us therefore allowing them to conduct skilful fast-paced aerial chases.    

Vertebrates’ eyes began as simple light receptors 550 million years ago during the Cambrian period in proto-fish animals. Carnivorous dinosaurs like Tyrannosaurus Rex had binocular line of sight which could provide depth perception and distance management while fighting and chasing prey.  Allosaurus’ head crest had a poorer overlap but could still succeed with an ambush predator strategy.

Rabbits have 360 degree vision and can see around and high up. Their vision is not 3 dimensional but could provide an all-round alarm system.

100 million years ago, mammals evolved night vision to stay out of the way of big dinosaurs and to exploit nightfall to feed and scavenge.  Large corneas allow more light to hit the retina and allow nocturnal mammals to succeed in the dark. Tarsiers have huge eyes which are almost all cornea and these eyes are bigger than their brains and skulls. Their eyes bulge out of their skulls and are held down by extra strong connective tissue. They then have to compensate for immovable eyes with the help of a neck which can turn 180 degrees.  Big cat eyes have a double retention system to capture light protons which produce eye shine that allow them to see their prey in the dark 6 times better than us.    

Eagle’s eyes are huge. Eagles are much lighter and smaller in size than us but their eyes are the same size as our’s. Their eyes also have 5 times the image resolution and are able to see 3 times further as compared to us.

Our primate ancestors evolved eyes that have good colour vision which allowed them to see red. Red leaves are younger and more nutritious. Binocular vision also allowed them to navigate throughout the tree tops and execute hand-eye coordination. But this made them vulnerable to predation from behind/from the skies. Primates then responded with group living and used communal vision to keep wary of predators. This group living then pushed the brain to evolve a bigger brain to understand and execute more sophisticated social interactions

The Permian extinction

The ancient mass extinction of the Permian geological period happened 250 million years ago. 95% of the species went extinct! Scientists have found evidence that volcanoes spilled out large amounts of CO2 which led to global warming and heated up the Permian ocean. Warm water cannot retain much oxygen and Hydrogen sulphide then starts to produce from the bacteria thriving in such waters. Hydrogen sulphide permeated the late Permian ocean and bubbled out of the oceans and killed life in the oceans and then on land too.

NOVA: The evolution of Communication

Communication between prey and predator? Preys can communicate poison by their skin color, like the Dart frog for example. Therefore predators will tend to stay away from them.


Ants communicate via hydrocarbons and create odours for communication via such hydrocarbons. Each ant job have a different odour. Scientists have been able to create particular responses in ant colonies by using dummy ants with various ant job odours.


The “Milky sea” phenomenon is created by bioluminescent bacteria who use chemicals to communicate with each other. Bacteria communicate to accomplish tasks that they would be unable to perform together: such as attacking a organism together or find food. These bacteria were lighting up to get fish to be eaten as they want to get into the stomach environments of fishes.

California ground squirrels use scent to mark territory. But these same scents leave behind olfactory cues that rattlesnakes use to hunt them Squirrels countered by chewing on shed rattlesnake skin and cloaked their scent by secreting it onto their own fur.

Scientists are now tracking whale communication via audio-detection buoy marker and satellites. Whale herds move over great distances in unison via very loud low frequency communication.

Wolf howls serve as communication of distance, location and as a form of defence (to indicate to enemies about the threatening size of their pack).

Song birds possess the most advanced vocal abilities. They can produce left and right frequencies. Sound penetrates their environment in 3 dimensions unlike visual communication which are easily blocked out by trees and foliage.

Chimps use body postures, hand signals, facial expressions and sounds to communicate. The similar areas in human and chimp brains light up when they communicate.