A couple of months ago I was lucky enough to receive a signed addition of David Attenborough’s book, Life on earth. The book co-exists alongside the TV documentary series of the same name, which was released the same year. Throughout, Attenborough’s style is as equally entertaining as it is within his many documentaries, and is full of as many interesting facts. Beginning with an outline of the variety of species on earth, each following chapter focuses on specific groups of organisms. Each is linked by the increasing complexity, lifestyle, or specialised adaptions within and between groups.
Attenborough’s style allows every group species to be equally respected, describing how those organisms with great simplicity are just as key to survival and evolution as those which are very complex. The intelligence and learning behaviour of flat worms for example is explored. The book goes on to explain an interesting phenomenon where by memory is shown to reside within a substance. An example is provided where one fresh water species was trained through morphic resonance to travel through a maze, and then killed. Following this the worm is fed to a second individual, which then completes the maze first time. When looking in to flatworms further, the ability to regenerate memory can also occur in a single worm itself. A paper following the Aspects of Neuroscience Conference (2015), explains how a group of scientists trained flatworms to travel towards light, despite not being a fan of it. Once this had been done the brain, which along with two lateral nerve cords makes up the planarian nervous system, was cut out. To discover if the regeneration of the brain would also cause regeneration of memories. After leaving the worms for a few weeks to regenerate, this in fact did occur and the worm continued to move towards the light. Although it is not quite understood, it is suggested that memory is stored in the nerve cords.
A couple more chapters in to the book how the evolution of flight first occurred in insects are explored, not only by looking at the advantages but the disadvantages and physical ability. An interesting point is addressed surrounding how wings occurred. Looking at the extant species of silverfish, two flaps like extensions can be seen on the thorax. As the silverfish is a flightless insect, they have no purpose for wings. The presence of these flaps therefore suggests that, like most adaptions in evolution, they previously had another role. The evolutionary theories around flight mainly focus around falling running or jumping being the cause, but these also focus on avian flight. Mammals however, instead adapted to glide, jump or swing through the sky but did not achieve the skill of flight, with the exception of bats.
One subject covered which is particularly of interest to me is mimicry, in this case the mimicry of plants. There are two key types of mimicry in animals, Batesian, a harmless species copying a harmless one and Mullerian, where two dangerous or distasteful species mimic each other. On the other hand, plants often also show Bakerian mimicry, a female mimicking a male, and Dodsonian, luring pollinators by mimicking other species. An example of plant mimicry is in the Late Spider Orchid produces one petal or flower which resembles the back of a female bee. As males see the bee image they are attracted to the flower, becoming coated in pollen and enabling reproduction of the plant to occur. Other species, also mimic scent, whist those such as the Bucket Orchid this a step further drugging pollinators. Not only looking attractive to particular bee species, but also mimicking the odour of the female. The greater the resemblance between the mimic and original species, the higher the chance of reproductive success.
With the complexity of the species increasing with each chapter, it makes sense that Attenborough focuses his final chapters on mammals. These cover the classic themes of Attenborough’s documentaries; possibly the most recognised being the fight between predator and prey, in this case described as ‘The Hunters and the Hunted’. It is the chapter just before these however, which caught my attention, beginning with a focus on the rather odd Platypus. Here the story about its discovery is told, a skin of seemingly random body parts being sent to London. Many at first believed it to have been a fake, sewn together as a ‘monster’. This apparently occurred frequently as ‘monster’ skins were sent from China. After careful examinations ruled out this theory scientist began exploring the creature. Being both warm blooded and covered in a thick, otter-like fur, it was concluded that the animal was a mammal. When an individual was then seen laying eggs therefore many were left confused. This confusion was only pushed further when the eggs hatched, as the young were fed and cared. In order to do this the female began producing a liquid from gland similar to mammalian sweat glands. The production of this milk like liquid is another common feature of mammals, but unlike most the platypus has not got any nipple like structures, meaning young are required to instead suckle from clumps of hair. Such confusion is also seen in other Australian species, such as the Spiny-Anteater, which also display a number of both primitive mammals and reptiles.
This book Attenborough shows what he does best. The detail and well explained examples make this book incredibly intriguing, whilst he is careful not to overcomplicate theories or place too much focus on to the need to fully understand it. For anybody who is interested in zoology or enjoys Attenborough’s documentaries, the book is worth a read. Especially if you enjoyed the TV series it accompanies. All of this information stated in this post is from the book unless stated otherwise. All photos are also from the book.
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