How can we thrive if we don’t conserve our natural environments and biodiversity?
Due to natural events, there have been five mass extinctions over the past 540 million years. There is a sixth mass extinction happening now, which we are responsible for. Our survival depends on the health of our planet’s natural ecosystems. We need to commit to conservation to ensure that our children, and their children, have a bountiful planet to live on.
Over the last 540 million years, the Earth has experienced five mass extinctions. During each, at least 75% of species became extinct in a relatively brief period of time. The fifth mass extinction occurred 66 million years ago. It featured the extinction of the non-avian dinosaurs along with the great majority of all plants and animals living at the time.
The fifth mass extinction was probably caused by the impact of a large comet or asteroid that drastically changed climates globally by throwing so much dust and debris into the atmosphere that photosynthesis was greatly reduced on a global scale.
Today, a sixth mass extinction is occurring – with extinction rates being higher than in the last 66 million years. Unlike previous episodes, this ongoing wave of extinctions is being caused mainly by humanity’s impact on the environment, rather than by natural events.
If all species that are currently threatened with extinction disappear, and if the current rate of extinction continues, we will reach the 75% threshold for a mass extinction in as little as three human lifetimes, or about 10 generations.
It is our responsibility to avert this sixth extinction and stop destroying the natural environments upon which the Earth’s biodiversity depends. An important first step is to realize that, far from being somehow apart from nature, we are as much a part of nature as any other organism, and as dependent upon it for our survival.
A good way to appreciate our place in nature is by examining the Tree of Life. The Tree of Life is an ever-evolving depiction of life’s common ancestry. The ancestry of each modern life form can be traced back along its branch to the origin of life at the base of the tree. This ancestor of all life forms was a single-celled organism that biologists call LUCA, the Last Universal Common Ancestor.
Bacteria were the first life forms to appear, while life forms that branched-off higher in the tree appeared progressively later in time. Most species have a more recent common ancestor than LUCA. For example, the most recent common ancestor of centipedes and flowering plants was an early eukaryote that lived about 1.6 billion years ago. More closely related species lie closer together on the Tree of Life and share a more recent common ancestor.
Humans have some genetic similarity to all living things – from animals to plants, fungi and bacteria. We are most similar to animals with whom we have shared the longest ancestries. The living species most closely related to us – the chimpanzee and bonobo – share 98% of our genes, and diverged from us evolutionarily some 6 – 7 million years ago.
All living species are related to each other to some degree because each inherited DNA, with modifications, from a long line of ancestors leading back to LUCA.
DNA is the common link among all species, past and present. The DNA of all species is made up of the same four nitrogen bases. The differences between species are in the number of nitrogen bases in each species’ genome and their sequences. DNA is what brings us all together.
The International Union for the Conservation of Nature (IUCN) assesses the conservation status of many species of animals and plants in its Red List of Threatened Species. Among a wealth of other information, the IUCN’s assessment as of 2015 reveals the following:
For animals, the IUCN has adequate data to assess the conservation status of 45,433 species. Of these:
- 1,228 species (2.7%) have become extinct or possibly extinct since 1500 A.D.
- 11,818 species (26.0%) are threatened with extinction.
- another 3,535 species (7.8%) are near threatened.
Among specific types of animals, here are the percentages of species that have become extinct since 1500, or are currently facing the threat of extinction:
- Primates (mammals most similar to humans) – 64%
- Mammals – 27%
- Birds – 15%
- Reptiles – 26%
- Amphibians – 42%
- Sharks and rays – 31%
- Bony fish – 23%
- Spiders and scorpions – 86%
- Insects – 27%
- Mussels and clams – 37%
- Crabs, lobsters and shrimp – 32%
- Snails – 46%
For plants, the IUCN has adequate data to assess the conservation status of 18,586 species. Of these:
- 249 (1.3%) have become extinct or possibly extinct since 1500 A.D.
- 10,896 species (58.6%) are threatened with extinction.
- another 1,583 species (8.5%) are near threatened.
To examine the IUCN Red List of Threatened Species, go to http://www.iucnredlist.org
To learn about the nature and extent of human impacts on our natural environments, go to The World Wildlife Fund’s Living Planet Report 2014 at http://www.wwf.org.uk/about_wwf/other_publications/living_planet_report_2014/ – .V-JnUTs2itA
Sixth Mass Extinction
The Earth is entering its sixth mass extinction. For an authoritative examination of the evidence for the current mass extinction, as well as its causes and consequences, see the 2015 article by Gerardo Ceballos and colleagues entitled, Accelerated modern human–induced species losses: Entering the sixth mass extinction. [Science Advances 19 Jun 2015: Vol. 1, no. 5, e1400253] http://advances.sciencemag.org/content/1/5/e1400253.full
Another Tree of Life
The Tree of Life diagram in the All from One exhibition is a simplified version of that depicted in a diagram from Science magazine’s Tree of Life Special Issue (2003). More up-to-date trees exist, and will continue to be revised as the genomes of more species are sequenced. Still, there is broad agreement among all versions, and the branching order of life forms shown in the tree here gives a good account of the history of life.
Science published an interactive online version of its tree, which can be found at http://www.sciencemag.org/site/feature/data/tol/. Visit this site to find out more details about the evolutionary relationships among the wide range of species living today.