How many complex species are there on Earth?

About 8.7 million.

And how many have we found to date?

About 1.2 million.

That is according to a recent study in PLoS Biology:

Knowing the number of species on Earth is one of the most basic yet elusive questions in science. Unfortunately, obtaining an accurate number is constrained by the fact that most species remain to be described and because indirect attempts to answer this question have been highly controversial. Here, we document that the taxonomic classification of species into higher taxonomic groups (from genera to phyla) follows a consistent pattern from which the total number of species in any taxonomic group can be predicted. Assessment of this pattern for all kingdoms of life on Earth predicts ~8.7 million (±1.3 million SE) species globally, of which ~2.2 million (±0.18 million SE) are marine. Our results suggest that some 86% of the species on Earth, and 91% in the ocean, still await description. Closing this knowledge gap will require a renewed interest in exploration and taxonomy, and a continuing effort to catalogue existing biodiversity data in publicly available databases.

Here is a table from the paper (click to enlarge) showing the vast difference in the numbers of catalogued and predicted species, which really highlights how little we know about life on our planet (particularly in the ocean).

An interesting calculation made in the study was the approximate cost and man power it would take to catalogue all of the species that are currently unaccounted for:

Considering current rates of description of eukaryote species in the last 20 years (i.e., 6,200 species per year; ±811 SD; Figure 3F–3J), the average number of new species described per taxonomist's career (i.e., 24.8 species, [30]) and the estimated average cost to describe animal species (i.e., US$48,500 per species [30]) and assuming that these values remain constant and are general among taxonomic groups, describing Earth's remaining species may take as long as 1,200 years and would require 303,000 taxonomists at an approximated cost of US$364 billion.

On the subject of species diversity, here is a nice 'tangled bush' image (click to enlarge then zoom in):

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Stephen Hawking ends speculation

Prof Stephen Hawking has roundly rejected the notion that he accepts the role of God in the creation of the universe. This was previously asserted by some creationists due to the following passage from A Brief History of Time:

If we discover a complete theory, it would be the ultimate triumph of human reason - for then we should know the mind of God.

It was clear to most people that Hawking was using poetic licence here, not actually talking about a literal God. But that obvious fact doesn't stop some from using the quote for their own means.

Anyway, confusion over...

Citing the 1992 discovery of a planet orbiting a star other than our Sun, in his new book, Hawking explains:

That makes the coincidences of our planetary conditions - the single Sun, the lucky combination of Earth-Sun distance and solar mass - far less remarkable, and far less compelling as evidence that the Earth was carefully designed just to please us human beings.

Also...

Because there is a law such as gravity, the universe can and will create itself from nothing... Spontaneous creation is the reason there is something rather than nothing, why the universe exists, why we exist... It is not necessary to invoke God to light the blue touch paper and set the universe going.

Good man Steve.

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Interview with an Event Horizon

In the recent edition of Nature there is a rather odd interview. Not wanting to be outdone by Oprah and Ellen, they have gone for an extreme A-list guest. None other than...

...an Event Horizon!!

This should be interesting.

When asked about the origin of life, the Event Horizon answers:

Biological life as you know it originated in your universe 13½ billion years ago in the heart of heated comets. Heat and cosmic radiation bombarded the carbon dioxide, methanol and ammonia they carried. As they neared their star during their elliptical orbits, the comets' frozen cores thawed, allowing those chemicals to interact in a semi-liquid medium and form rudimentary organic compounds — proteins and amino acids, the building blocks of life. Streaking past the six worlds of this solar system, they rained down those organic compounds in dust that settled in the planet's atmosphere and, eventually, onto its surface. On those planets with a heat source and a liquid medium, these compounds formed lipid membranes that facilitated the formation of self-replicating cells. These evolved into bacteria that over eons developed into simple bio-organisms, the first step in the slow, inexorable climb towards complexity. This process has repeated itself countless times throughout the cosmos over billions of years. This is why your universe teems with biological life.

Non-biological life incubates in the cool ether of dark matter shaped by processes beyond your current level of understanding. However, if our experience is any indication, in time you will come to know such life forms and recognize them as your brothers. In every universe we've explored, biological and non-biological life forms inevitably join together and lift each other to magnificent new heights.

OK, sounds reasonable-ish.

But when asked if God exists, the Event Horizon has this to say:

Everything in existence has a creator, ad infinitum. Before the Big Bang there was neither time nor space nor matter, but consciousness. Formless. Eternal. Contemplating its creator. And contemplating others like itself that might exist across the infinite bubbles of reality. As time did not exist, we cannot say whether this omni-consciousness existed for a millisecond, a millennium or an eternity. But it jabbed with its thoughts at the weathered fabric between realities and poked an infinitesimal hole. And the entirety of a neighbouring universe — endless space and matter — flooded through that pinhole in a spectacular cosmic eruption. The omni-consciousness found that matter, gave it form, and it revelled in its multitudinous shapes. It discovered that matter — moulded by the flame of time and the winds of evolution — could eventually give rise to its own self-aware components, part of the omni-consciousness, yet separate from it. It delighted in each of the quadrillions of consciousnesses that flickered into and out of existence. It no longer knew loneliness. Time, space and matter continued to expand — prodded into acceleration by the omni-consciousness — hoping in vain to fill every crevice of infinity. This has happened in every bubble of the transreality-froth we've explored.

Hmmm, if you listen hard enough you can hear the gerbil at the Discovery Institute frothing at the mouth as he turns on his laptop...

Of course, this interview is just a bit of a joke.

The 'interviewer' is a chap named Mercurio Rivera, a science fiction writer. The reason Nature have published this is to celebrate the 50th anniversary of the inaugural publication of SETI, entitled "Searching for Interstellar Communication". They have also published an article by Fred Kaplan reflecting on the origins, impacts and legacy of this paper and of SETI itself.

Happy birthday!!

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Nature review: Origin of 'RNA world'

OK this is cool. Really cool. But I suck at chemistry so I'm gonna keep it real simple...

It's a given that life somehow emerged at least once on this planet about 4-4.5 billion years ago. Understanding how this amazing event happened is a major challenge though. There are a multitude of theories out there but problems tend to arise in trying to reproduce the origin of life event in the lab. One theory is that prior to DNA and protein-based life there was an exclusively RNA-based world. Indeed, this theory is probably widely accepted as the most plausible, if not the only possible, scenario.

As I said, each theory has it's own problems, and the RNA-world theory is no different. The main difficulty is how to combine the three elements of an RNA molecule, i.e. the nucleobase, the ribose and the phosphate. In particular, attempts to join together the nucleobase and the ribose have always been met with failure, casting doubt on the likelihood of these molecules spontaneously combining in Earth's early atmosphere...

That is until now.

Researchers Powner et al (1) have published results in Nature showing that a nucleobase and a ribose can combine in plausible early Earth conditions. They achieved this by using a totally different approach to previous attempts. It had long been assumed that the nucleobase and the ribose must have first formed independently and then joined together in a secondary reaction (See FigA). Instead, Powner and colleagues have now shown that the combined nucleobase-ribose molecule can emerge from a precursor molecule, side-stepping the need for both to first form independently (FigB). Specifically, "activated pyrimidine ribonucleotides can be formed in a short sequence that bypasses free ribose and the nucleobases, and instead proceeds through arabinose amino-oxazoline and anhydronucleoside intermediates"


Figure taken from article by Jack Szostak (2)

So this work gives a plausible mechanism for the origin of the 'RNA world'. Pretty cool, isn't it?

Well yes, but I've saved the best part till last.....

The catalyst for this series of reactions that combine a nucleobase and a ribose is........wait for it......

Phosphate!!

That's right. The third component of RNA is needed for the precursor molecules to form the activated pyrimidine ribonucleotides. Phosphate controls several steps in the reaction. Specifically, it "controls three reactions in the earlier stages by acting as a general acid/base catalyst, a nucleophilic catalyst, a pH buffer and a chemical buffer". Following completion of it's job as a catalyst, phosphate is then incorporated into the molecule at a later stage, thus completing the RNA synthesis. The beauty of this system is incredible, and is described perfectly by Szostak:

Phosphate continues to have several essential roles in the remaining steps of Powner and colleagues' pathway, in one case causing depletion of an undesired by-product, and in another saving a critical intermediate from degradation. The penultimate reaction of the sequence, in which the phosphate is attached to the nucleoside, is another beautiful example of the influence of systems chemistry in this set of interlinked reactions. The phosphorylation is facilitated by the presence of urea; the urea comes from the phosphate-catalysed hydrolysis of a by-product from an earlier reaction in the sequence.

This work represents a major breakthrough in our understanding of how life might have emerged as it has provided an elegant mechanism for the spontaneous generation of RNA. As always, more research needs to be done, but we now have an exciting new perspective on an age-old problem.


(1) Powner et al. Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions. Nature 459, 239-242 (14 May 2009)

(2) Jack W. Szostak. Origins of life: Systems chemistry on early Earth. Nature 459, 171-172 (14 May 2009)

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