31 A Tree Grows in Manhattan

Back

David B. Wake

543

When the first full genome for a microbe was published, I

was teaching an evolution course, and as I read the article I

was first surprised and then thrilled to learn that the discovery

had such profound evolutionary significance. Along with

many others, I realized that we were entering a new world,

one in which evolutionary biologists such as I had new responsibility.

We now could, and therefore must, build a Tree

of Life. It has long been a dream of comparative biology to

explain how life has evolved and what evolutionary relationships

mean. It has been a personal dream to make evolutionary

biology predictive. Because evolution seems to run in

grooves, following avenues of least resistance, knowing something

about one taxon gives one a very good sense of what a

closely related taxon will be like. Why should this be so?

Evidently there are rules to be discovered, generalities to be

established. Genetics, especially as it relates to development,

provides some inspiration. But imagine what we might learn

if we knew the true Tree of Life! Such a tree would include

vastly more than what I now have the courage to identify as

“only” full genomic information, but even that would be a

great start.

It has been nearly 20 years since my colleague Allan

Wilson first told me about how it was possible to amplify and

soon to sequence DNA. He thought it would be only a short

time before systematists would be routinely sequencing DNA

and using the data to frame and test evolutionary hypotheses.

I thought he was optimistic, but he was right. About

the time that these conversations were taking place, Marvalee

Wake and I bought our first personal computer (we actually

thought it would be possible to share one!). Systematists

everywhere were having such experiences, and before long

we were armed with methods, techniques, machines, and

most important, with an intellectual framework (coming out

of the phylogenetics revolution starting with Hennig on the

one hand and numerical methods on the other, in the 1960s).

Rapid progress ensued, leading to the first inkling that we

might try assembling a Tree of Life, envisioned in the Nobel

Symposium in Sweden in 1988. But most of us toiled with

our own taxa, which systematists have historically divided

up so as to avoid direct confrontational competition. The

organization of the systematics community into provincial

societies (within the herpetological community alone there

are three mainly North American societies and dozens more

elsewhere in the world, most with their own journals) did

not help bring groups together, but gradually, with the National

Science Foundation playing a critically important role

at several points along the way, we began to interact effectively,

and the successful conference we have experienced is

the most recent manifestation.

Not surprisingly, early attempts to develop a tree of all

life began within the community of microbial biologists, not

only because they had less (in the sense of organismal complexity)

to work with and had to turn to molecules, but also

because they already were familiar with many molecular biological

techniques and were ready to move when the era of

PCR (polymerase chain reaction) arrived. Perhaps more sur544

Perspectives on the Tree of Life

prising is how rapidly the systematics community embraced

molecular methods and approaches, not as a replacement for

more traditional morphological approaches (which continued

to develop methodologically, with a focus on building

large character-based databases and analyzing them in diverse

ways), but as an exceedingly important addition to our “tool

kits.”

The New York meeting was an unqualified success from

my viewpoint. The oral presentations were uniformly outstanding—

well prepared, well delivered, and designed for

effective communication with a diverse audience. Remarkably,

there was no dissent from the fundamental premise

—that we want, need, and can produce a Tree of Life.

Furthermore, in a field that has experienced intellectual warfare,

what controversies arose in terms of data analysis and

the like were downplayed in the interests of the general good.

Perhaps we were all on good behavior because of the high

degree of idealism expressed so beautifully by Ed Wilson in

his inspiring opening address, and the symbolism of a remarkable

address by Rita Colwell, the Director of the National

Science Foundation and a person who thoroughly understands

and appreciates the goal we have set for ourselves. For

whatever reason, there was a wonderful sense of a common

purpose, as well as of duty and responsibility. And in the

background of it all was the intellectual imperative that the

tools are at hand to accomplish our goal.

It is amazing to me how much comparative DNA sequence

is accumulating and at what a high rate! Lacking such

data, we would not even be talking about a Tree of Life initiative,

but for taxon after taxon we witnessed the impact of

molecular data. In some instances the goal of many systematists,

a “total evidence” approach incorporating morphological

and molecular data, integrated with fossil evidence, is

emerging (e.g., mammals). However, large molecular databases

do not assure phylogenetic resolution, as we have learned

in the case of birds. For some relatively large taxa (e.g., my own

group, the amphibians, with about 5500 species), it may be

possible to obtain sequence information for nearly all species,

so as to put the “leaves” on the tree. But for microbes (astonishingly

complex in the extent of paraphyly), despite an

enormous accumulation of sequence data, the number of

unsampled taxa is staggering and one wonders what the impact

of as yet unsampled lineages will be.

I was struck by the estimates of one after another of the

specialists that the numbers of taxa in their areas were vastly

greater than previously thought. We remain in a phase of

discovery, as we were reminded by the very recent description

of a new order of insects. The number of species of

amphibians is growing more than 3% per year, and vertebrates

are supposed to be well known. Certainly at the level

of basal taxa we have a great deal to learn, even for our bestknown

groups. So, the task is large, and if we are to accomplish

it we will have to modify our publication strategy and

streamline the process by which we describe taxa.

There will be more Tree of Life conferences and they will

become increasingly inclusive, of researchers as well as taxa.

We will work together not only because we stand to benefit

from the interaction, but above all because we must. Information

about what we have in the world will improve our chances

of preserving biodiversity. Just knowing the Tree of Life will

not assure its preservation, but for those of us for whom taxa

count and trees count, having the requisite information will,

we expect, enable us to more effectively act. We live in challenging

and exciting times, but they are perilous as well, and

it will take more than knowledge and wisdom to preserve the

main structure of the Tree of Life on this planet.

Навигация