The aquatic ape hypothesis is still wrong

An article in the Guardian says that at a conference next week, David Attenborough will voice his support for the aquatic ape hypothesis. I grew up watching Attenborough documentaries. I am a huge fan and would credit him with helping to ferment my interest in biology. But, I am no fan of the aquatic ape hypothesis because it  is adaptationist and fails to provide parsimonious explanation for human evolution.

The aquatic ape hypothesis tries to force large number of human traits together under one umbrella explanation, that our ancestors had a close association with water. But no time period in the history of our evolution is specified and the fossil record shows that the traits claimed to have evolved in association with water appeared at widely different times. Without good fossil evidence demonstrating a strong association with water the hypothesis is dead... in the water.

The hypothesis is driving the evidence presented, not the other way around as it should be in science. A mish-mash of highly derived and rudimentary adaptations to water are used as evidence. Few of these are consistently associated with aquatic animals, such as hairlessness, which is present in several terrestrial mammals and absent in the majority of aquatic mammals. There are also a number of features that we humans have that are inconsistent with aquatic ancestry, such as internal testicles. 

I am at a loss to explain how the aquatic ape hypothesis keeps getting coverage in popular press given how weak it is as an explanation. I get that human evolution is interesting, but it is such a bad explanation on the basis of both evidence and the methodology of its proponents. It's the phlogiston of explanations for the evolution of human traits. Fortunately, the recent coverage has spawned some well deserved ridicule, which has had a strong response on Twitter.

Cooperative hunting between species

Cooperative hunting among individuals of the same species is common. But, cooperative hunting between different species is incredibly rare. Ed Yong has an interesting story on cooperative hunting between moray eels and grouper. Although this behaviour was first documented in 2006, there is a new study that describes a previously undocumented behaviour that the grouper uses to recruit its hunting partners.

Why fund science research?

It's an easy question to answer. Science is economically and culturally important. 

As Phil Plait discusses on Bad Astronomy, Stephen Moore of the Wall Street Journal says that we shouldn't fund basic research because it is innovation in industry that brings the economic returns. That is nonsense. Industry innovation would come to a shuddering halt without basic research. It's curiosity-driven research that provides the fuel that industry uses to produce new products.

Funding science provides more than a return on investment. It's also about understanding the natural world. The Universe is a fascinating place and we humans (with exceptions like Stephen Moore) are deeply interested in finding out about it. To me, the accumulation of knowledge should be viewed as the primary goal of science. Commercialisation of that knowledge is just a welcome side effect.

The resilience of coral reefs

Many people are justifiably concerned with the potential impacts of climate change and ocean acidification on coral reefs. But, coral reefs have been declining for at least the last 25 years and probably much longer, overwhelmingly due to threats that are unrelated to climate change. If we do not address these impacts we will continue to lose coral cover and reefs will be more vulnerable to climate change and ocean acidification.

A coral outcrop on the Great Barrier Reef (photo Wikipedia)

A new paper serves as an illustration of how resilient coral reefs are to climate impacts when they are isolated from other anthropogenic impacts, such as overfishing and agricultural runoff. James Gilmour and other researchers from the Australian Institute of Marine Science and some from the Centre of Excellence for Coral Reef Studies followed the recovery of the Scott Reef system after a catastrophic bleaching event in 1998 that reduced coral cover from 50% to 10%. There was great concern for the reef system because it was isolated from other reefs that could supply coral larvae to fuel recovery.

The Scott Reef system. The crescent shaped reef at the bottom is Scott Reef South, the small reef above the left arm of the crescent is Scott Reef and the pear shaped reef is Scott Reef North (photo Wikipedia).

It turns out that, on balance, the isolation was a good thing. The supply of coral larvae reaching the reef was less than 6% of what it was prior to the bleaching event for six years. But, the reef was also isolated from chronic anthropogenic pressures, particularly overfishing. The number of herbivorous fish was already high at the time of the bleaching and jumped afterwards. As coral cover increased the numbers of herbivorous fish declined back to what they were prior to the bleaching.

The daisy parrotfish, Chlorurus sordidus, is an important herbivore on coral reefs (photo Dennis Polack, EOL).

The herbivorous fish kept seaweed and other organisms that compete with coral from taking over. Remnant corals that survived the bleaching were able to grow quickly and the small numbers of coral larvae reaching the reef had unexpectedly high survival. The fast growth of existing coral drove the initial recovery of the reef. Once young corals became established and began reproducing the supply of larvae increased and the recovery of coral cover accelerated.

Ten years after the bleaching event the supply of coral larvae had returned to the levels seen before the bleaching. Two years later the amount of coral cover and community structure on the reef had largely been restored. The rate of recovery is made more remarkable by the occurrence of a second more moderate bleaching event, two cyclones and a disease outbreak.

The study highlights just how resilient coral reefs can be to the effects of climate change and other disturbances if chronic anthropogenic stress is low. Overfishing, sedimentation and pollution are causing severe declines in coral cover right now. If we can control these threats, coral reefs might be able to survive in a warmer, more acidic ocean.

Reference:

Gilmour, J., Smith, L., Heyward, A., Baird, A., & Pratchett, M. (2013). Recovery of an Isolated Coral Reef System Following Severe Disturbance Science, 340 (6128), 69-71 DOI: 10.1126/science.1232310

In the cave of the blind, the no-eyed crab is king

Cave dwelling creatures are often blind. The prevailing view is that, in such species, mutations in the visual system have little or no effect on fitness and vision is lost as these mutations gradually accumulate. There are several other types of characters that we can be reasonably confident are adaptations to life in caves, such as elaboration of structures for touch or smell. However, it is often hard identify which population cave adapted species are descended from and, therefore, how long ago they invaded caves. Without this information it has been hard to test ideas about the evolution of traits associated with life in the dark.

A cave form of the fish, Astyanax mexicanus, which is eyeless and unpigmented, traits typical in caves. It is a commonly used model species in studies of adaptation to cave environments (photo Wikimedia Commons).

Sebastian Klaus and colleagues from the National University of Singapore and Goethe University examined five species of freshwater crab in the genus Sundathelphusa, which occur on Bohol Island in the Philippines. Four species are only found in caves and the other has established several populations in caves. The repeated invasion of caves by the crabs has led to varying degrees of adaptation to life in the dark within the group. 

Freshwater crabs in the genus Sundathelphusa from Bohol Island. Thy are arranged from least cave adapted (top) to most cave adapted (bottom). From top to bottom the species are Sundathelphusa boex, S. vedeniki, S. urichi, S. sottoae and S. cavernicola (from Klaus et al. 2013).

The team used genetic data to estimate the time at which each species and population last shared a common ancestor. They then compared several features of cave-adapted crabs with their closest terrestrial relatives. Reductions in the visual system were just as pronounced as changes in cave-adapted features, indicating that evolution occurs at similar rates. The authors argue that this is a clear sign that eye loss is under directional selection because changes should appear more slowly if they are a result of selectively neutral mutations. 

They don’t speculate at all about what might favour eye-loss in the Bohol crabs, but hint in the introduction that it could be due to trade-offs between vision and other sensory systems. Trade-offs occur where increasing one aspect of fitness necessarily requires the reduction of fitness in another. If eyes are energetically costly to build and maintain then retaining functional eyes might prevent greater investment in other senses. Trade-offs are ubiquitous in biology and have been implicated in the loss of eyes in other cave dwelling species.

While I was doing research on this study I came across several creationist websites that argue cave adapted creatures are strong evidence that evolution is false because a trait is lost. According to them this shows evolution progressing in the wrong direction to what is predicted. They argue that evolution should progress towards more information and greater complexity. This is incorrect and shows, yet again, that creationists typically have a poor understanding of evolutionary theory.

The 'logic' of this argument is similar to the idea of a "Great Chain of Being", which pervaded early thinking about biology. This type of thinking is where we get several antiquated, but persistent terms, such as "missing link" and "highly evolved". It continues to dog evolution in the way that evolutionary information is often presented, such as the placement of organisms more closely related to us at the right or top of phylogenetic trees and at the end of textbooks.

The phylogeny of primates with humans at the top and less related groups at the bottom (from Wikipedia).

Linear descent was never part of Darwin's theory, nor was an increase in information ever a necessary assumption on which evolutionary theory rests. When you look at an evolutionary tree (like the primate tree above), all of the living species at the branch tips have an equally long evolutionary history. They are not descended from each other, they are descended from a common ancestor. You could say that they are equally evolved.

The first evolutionary tree drawn by Darwin over 20 years before the publication of On the Origin of Species.

Evolution doesn't prevent information from increasing, but contrary to the creationist claims it does predict that there will be strong limits on it. Both single trait and multi-trait trade-offs are thought to prevent organisms from becoming perfectly adapted. Single trait trade-offs occur where elaboration of a structure increases fitness in one environment, but reduces it in others. Multi-trait trade-offs occur where two or more structures are dependent on a shared finite resource.

Blind crabs are not evolving in the wrong direction. There is no wrong direction, they're just evolving under the constraint of trade-offs. Eye reduction and loss of pigmentation are not the only evolutionary changes that are occurring either. Other traits are becoming more elaborated, such as the length of their legs and the hairs on their claws, suggesting a multi-trait trade-off. This result is not only consistent with evolutionary theory, but expected.

An abbreviated version of this post is published on the Australasian Evolution Society website in the Research Highlights section.

Reference

Klaus, S., Mendoza, J., Liew, J., Plath, M., Meier, R., & Yeo, D. (2013). Rapid evolution of troglomorphic characters suggests selection rather than neutral mutation as a driver of eye reduction in cave crabs Biology Letters, 9 (2), 20121098-20121098 DOI: 10.1098/rsbl.2012.1098

Research Highlights from the Australasian Evolution Society

I have been asked by the Australasian Evolution Society to provide some 'Research Highlights' for their newly launched website. The Research Highlights promote interesting recent research by evolutionary biologists in Australasia. To get more diversity in the types of research covered there will be two or three others writing too. My stories will go up every few weeks and I will endeavor to publish them here as well, probably with some additional comments. My first piece went up a few weeks ago and I've submitted my second, which should go up shortly. I'll post here as soon as it is.

My favourite science books

I've been talking to a few people recently about good science books. My favorite books that deal with similar topics to this blog are in descending order:

Mapping the deep - Robert Kunzig

The World without us - Alan Weisman

The wavewatcher's companion - Gavin Pretor-Pinney

Trilobite - Richard Fortey

At the water's edge - Carl Zimmer

Books outside the topic area of this blog that I found to be excellent are:

The demon-haunted world - Carl Sagan
The elegant universe - Brian Breene
Chaos - James Gleick

Neil Shubin's "Your inner fish" is sitting on my bookshelf just waiting to be read. I hear it is very good and will probably make it onto my list. Several books by Dawkins and Gould are also among my favorites, but I liked them less than the ones above. The ancestor's tale (Dawkins) and Wonderful life (Gould) are probably the best I've read of their books.

China's thirst for development

China is noted for its rapid development often at severe cost to the environment. The Australian newspaper reports that more than half of the rivers in China are missing. In the 1990s there were over 50,000 rivers on maps of China, but in a recent national water census surveyors were only able to locate 22,909 of them. Destruction of the environment due to rapid development and the unsustainable use of underground water supplies are thought to be among the main culprits. The government though, is blaming climate change and cartographers mistakes for the missing rivers.