Life on Earth (Part 1)

Life on Earth (1979)I am currently watching the highly acclaimed and fascinating twelve part television natural history series Life on Earth: A Natural History by David Attenborough, in which Sir David Attenborough travels the globe in order to trace the story of the evolution of life on the planet. it is the first in Attenborough’s ‘Life’ series of programmes and was followed by The Living Planet. The first episode “The Infinite Variety” begins in the South American rainforest where the rich variety of life forms is used to illustrate the sheer number of different species, and how many are dependent on others for food or means of reproduction, David Attenborough argues that they couldn’t all have appeared at once. So To discover which came first, and the reasons for such diversity he sets out on an epic journey which takes him all over the world from the Galapagos Islands, the Grand Canyon, Lake Superior in Canada, Australia and Yellowstone Park in Wyoming.

The next episode “Building Bodies” explores the various sea-living invertebrates and traces the The evolution of shelled creatures, from the flatworm, which eventually changed its body shape when burrowing became a necessity for either food or safety and developed shielded tentacles and casings which eventually enveloped the entire body, and became molluscs, including single-shelled such as the cowrie, bivalves including scallops, giant clams & the nautilus, and how they also evolved into species like the ammonites, sea lilies, starfish and sea urchins on the Great Barrier Reef how animals like the Trilobites and Crustaceans including the Horseshoe Crab and The Robber Crab formed the next evolutionary step.

The next episode “The First Forests” examines the earliest land vegetation and insects. and how the Crustaceans eventually evolved to live on land. Descended from segmented sea creatures, millipedes were among the first to take advantage of such a habitat and were quickly followed by other species. Without water to carry eggs, bodily contact between the sexes was now necessary. This was problematical for some hunters, such as spiders and scorpions, which developed courtship rituals to ensure that the female didn’t eat the male. The first plants were mainly mosses and liverworts however Over time, the plants’ cell walls strengthened and they grew taller these included Ferns and horsetails. Insects then evolved wings to avoid climbing and the dragonfly (which once Meganeura had a wingspan of 60 centimetres). Some plants, like the cycad enlisted the insects to transport pollen, while others, like the conifer, spread spores. Meanwhile the giant sequoia of California is the largest living organism of any kind: which grows to a height of 112 metres, secretes resin to repair its trunk, and this survives as amber. Within it, insect specimens have been found that are 200 million years old.

The fourth episode “The Swarming Hordes” details the relationship between flowers and insects. of which There are some one million classified species of insect, and two or three times as many that are yet to be labelled. Around 300 million years ago, plants began to enlist insects to help with their reproduction, and they did so with flowers, because although plants contain both male and female cells, pollination from another plant is preferable as it ensures greater variation and thus evolution. So Flowers advertise themselves by either scent or display. Some evolved to produce sweet-smelling nectar and in turn, insects developed their mouth parts into feeding tubes in order to reach it. However, to ensure that pollination occurs, some species — such as the orchid — have highly complicated mechanisms that must be negotiated first. Others, such as the yucca and its visiting moths, are dependent on one another. To take advantage of the visiting insects many predators such as the mantis and Crab Spider, are camouflaged to match the flowers and leaves visited by their prey. The Life-cycle of some insects is quite complicated – They hatch from eggs develop from Larvae Metamorphosise inside a coocoon before emerging as an adult. Most insects are small and to overcome this some insects like Ants, Termites, Bees and wasps became social and grouped together to form massive colonies to help them survive.

The fifth episode “Conquest of the Waters” looks at the evolution of fish, who have developed a multitude of shapes, sizes and methods of propulsion and navigation, from primative fish like the The sea squirt, the lancelet and the lamprey to the first back-boned fish which appeared about 400 million years ago. He finds Fossil records of the earliest fish to have developed jaws, the lateral line, swim bladders and Gills for breathing. These evolved into two shapes of creature with cartilaginous skeletons: wide ones (like rays and skates) and long ones (like sharks) and fully boned species that inhabit oceans, rivers and lakes. Coral reefs contain the greatest variety of species, many of which are conspicuously coloured to ward off predators or attract mates, however the open ocean offers no such refuge, so as there is safety in numbers both hunters and hunted swim in shoals and have streamlined bodies for pursuit or escape. Some never before seen fish live in the icy depths of the ocean and have developed a veriety of bizarre shapes to cope with the extreme conditions.

The sixth installment “Invasion of the Land” describes the move fish made from water to land and how they evolved into amphibians. and looks at a 450 million-year-old fossil of a amphibian called eusthenopteron that possessed both limbs for mobility and lungs to breathe and how it may have evolved from lungfish which are able to absorb gaseous oxygen and coelacanths, an ancient fish with bony fins that could have developed into legs. The episode looks at different groups of Amphibians like The Caecilians, who have abandoned legs altogether and live underground, newts and salamanders who need to return to the water to allow their skins to breathe and Frogs and Toads which have evolved into many different species such as the Goliath Frog, The Tree Frog, whose webbed feet form parachutes that turn them into “dazzling athletes”, with some species being able leap over 15 metres — 100 times their body length, and the Poison Dart Frogs, which are highly toxic, and deter predators by being brightly coloured. How frogs get round the problem of finding a mate by “singing” and the some of the extraordinary methods employed in breeding are examined, including laying eggs in rivers, depositing them in other damp habitats for safety or, as with the Brazilian pipa, embedding them within the skin of the parent itself.

However Amphibians have one disadvantage, they need lots of water to survive and episode seven “Victors of the Dry Land” is devoted to the evolution of reptiles and shows how reptiles evolved a scaly watertight skin to get round the problem of drying out. Scales also protect the animal from predators and can also provide an effective means of camouflage & it means They are not as restricted as their amphibian ancestors, and can survive in the hotter climates. Because reptiles do not need to return to water to breed they also evolved internal fertilisation and a watertight egg, which hatches fully formed young (Vivaporous) . However reptiles can’t generate body heat internally or sweat to keep cool. Therefore, they rely on the sun and areas of shade. Different types of reptile are looked at including the Nile Crocodile and snakes, including The boa Constrictor, puff adder and sidewinder who lost their legs and started burrowing instead and have developed a surprising array of methods for getting about and some extreme adaptations for survival including the egg-eating snake which has an extreme example of a hinged jaw, and the diamondback rattlesnake which is described as the most efficient killer.

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