Friday, 27 October 2017

Sticking It To Creationists With An Early Tree

World's oldest and most complex trees - News - Cardiff University

Another scientific paper which quite incidentally and without effort or intent, refutes a key creationist claim, was published yesterday.

It was nothing more sensational from a biology perspective than the discovery that the earliest trees were much more complex in the structure of their trunks and in their growth patterns than modern trees.

The key creationist claim is that 'macro'-evolution is impossible because it involves an increase in complexity which needs an increase in genetic information which, so they claim, is impossible because er... well... um... something to do with the Second Law. No, don't ask; you'll never get a coherent answer.

And yet, as this discovery by a group of scientists based at Cardiff University, UK, shows, at an early stage in their evolution tree were much more complex, so modern trees must have evolved by becoming less complex.

This is nothing new to biology because evolution does not require an increase in complexity and often involves a reduction - endoparasitic worms, for example, are usually less complex than their free-living relatives. Salamanders frequently have very much larger genomes than reptiles, bird and mammals.

So back to these complex, 'primitive' trees. As the Cardiff University press release says:

The first trees to have ever grown on Earth were also the most complex, new research has revealed. Fossils from a 374-million-year-old tree found in north-west China have revealed an interconnected web of woody strands within the trunk of the tree that is much more intricate than that of the trees we see around us today. The strands, known as xylem, are responsible for conducting water from a tree’s roots to its branches and leaves. In the most familiar trees the xylem forms a single cylinder to which new growth is added in rings year by year just under the bark. In other trees, notably palms, xylem is formed in strands embedded in softer tissues throughout the trunk.

The body of these tree trunks remained hollow and quickly filled with sand so the few rare fossils had little of the fine detail preserved. However, this specimen from China was preserved in glassy silicate from volcanic sediment, allowing even single cells to be examined.

The evolution of trees and forests in the Mid–Late Devonian Period, 393–359 million years ago, profoundly transformed the terrestrial environment and atmosphere. The oldest fossil trees belong to the Cladoxylopsida. Their water-conducting system is a ring of hundreds of individual strands of xylem (water-conducting cells) that are interconnected in many places. Using anatomically preserved trunks, we show how these trees could grow to a large size by the production of large amounts of soft tissues and new wood around the individual xylem strands and by a controlled structural collapse at the expanding base. We have discovered a complex tree growth strategy unique in Earth history, but with some similarity to that of living palms.

Cladoxylopsida included the earliest large trees that formed critical components of globally transformative pioneering forest ecosystems in the Mid- and early Late Devonian (ca. 393–372 Ma). Well-known cladoxylopsid fossils include the up to ∼1-m-diameter sandstone casts known as Eospermatopteris from Middle Devonian strata of New York State. Cladoxylopsid trunk structure comprised a more-or-less distinct cylinder of numerous separate cauline xylem strands connected internally with a network of medullary xylem strands and, near the base, externally with downward-growing roots, all embedded within parenchyma. However, the means by which this complex vascular system was able to grow to a large diameter is unknown. We demonstrate—based on exceptional, up to ∼70-cm-diameter silicified fossil trunks with extensive preservation of cellular anatomy from the early Late Devonian (Frasnian, ca. 374 Ma) of Xinjiang, China—that trunk expansion is associated with a cylindrical zone of diffuse secondary growth within ground and cortical parenchyma and with production of a large amount of wood containing both rays and growth increments concentrically around individual xylem strands by normal cambia. The xylem system accommodates expansion by tearing of individual strand interconnections during secondary development. This mode of growth seems indeterminate, capable of producing trees of large size and, despite some unique features, invites comparison with secondary development in some living monocots. Understanding the structure and growth of cladoxylopsids informs analysis of canopy competition within early forests with the potential to drive global processes.

Hong-He Xu, Christopher M. Berry, William E. Stein, Yi Wang, Peng Tang, Qiang Fu.
Unique growth strategy in the Earth’s first trees revealed in silicified fossil trunks from China.
Proceedings of the National Academy of Sciences
, 2017; 201708241 DOI: 10.1073/pnas.1708241114

Copyright © 2017 The authors
Reprinted under the terms of the PNAS License

There is no other tree that I know of in the history of the Earth that has ever done anything as complicated as this. The tree simultaneously ripped its skeleton apart and collapsed under its own weight while staying alive and growing upwards and outwards to become the dominant plant of its day.

Dr Chris Berry, Co-author.
Senior Lecturer, School of Earth and Ocean Sciences,
Cardiff University, Cardiff, United Kingdom
Of course, we don't know which, if any, modern trees evolved from these early ones, and true trees, as opposed to tree ferns and giant horsetails of which the Cladoxylopsida are believed to have been ancestors, could have evolved several times within the angiosperm order but it's none-the-less interesting that the earliest (and so usually regarded as the most primitive) trees were so complex. This complexity arose very early in the history of trees so this complexity must have evolved relatively quickly. If there are living descendants, then they lost this complexity relatively quickly and settled into a simpler form.

As the authors point out, to understand this structure and growth pattern, we need to understand canopy competition, i.e., the competition for light between the trees in a forest. This is a powerful driver of evolution so this may have been an example of a solution that works but is not very efficient. The trunk appears to have gradually collapsed under it's own weight meaning it's 'skeleton' was torn apart and healed. There was an obvious cost to this process which was reduced by building a stronger, more stable trunk.

Canopy competition, driving trees to engage in an evolutionary arms race, is a prime example of the way a mindless, unplanned evolutionary process can produce an enormous amount of wasted effort and resource, but which evolving species have no option but to indulge in. Ultimately, little or nothing was gained by trees in this competition for light resource since each species would have done just as well had they all remained as ground level - as a single intelligent designer would surely have designed them. Yet this arms race seems to have driven this early tree to evolve a utilitarian quick fix that had to be modified and made more efficient later on.

It's a maxim of design that good design is minimally complex, so here we have an example of bad 'design' and evidence that no intelligence was involved. Creationists who have been fooled into believing that complexity, not simplicity' is evidence of intelligent design, could usefully look at this tree and ask themselves why then did trees evolve to be less complex?

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