WEBVTT

00:00:00.000 --> 00:00:01.340


00:00:01.340 --> 00:00:03.560
- Charles Darwin
famously compared

00:00:03.560 --> 00:00:06.770
the evolutionary relationships
between different species

00:00:06.770 --> 00:00:09.680
to the branches of a
tree, all originating

00:00:09.680 --> 00:00:11.760
from a common ancestor.

00:00:11.760 --> 00:00:14.210
Historically, an
organism's position

00:00:14.210 --> 00:00:15.920
on the tree was
simply determined

00:00:15.920 --> 00:00:19.700
based upon its observable
characteristics or phenotype,

00:00:19.700 --> 00:00:24.290
such as the presence of
leaves, a spine, or eyes.

00:00:24.290 --> 00:00:26.690
Extinct species could
be placed on the tree

00:00:26.690 --> 00:00:30.350
in a similar fashion using
phenotypic traits preserved

00:00:30.350 --> 00:00:32.880
in the fossil record.

00:00:32.880 --> 00:00:36.420
Shortly after Darwin published
on the Origin of Species,

00:00:36.420 --> 00:00:41.440
Heckel proposed Three Kingdoms
of life in 1866, plants,

00:00:41.440 --> 00:00:45.960
animals, and protus, which were
neither plant nor animal based

00:00:45.960 --> 00:00:48.510
on easily observable phenotypes.

00:00:48.510 --> 00:00:51.780
Eventually, the distinction
between plants and animals

00:00:51.780 --> 00:00:55.830
was found to be less important
than previously proposed.

00:00:55.830 --> 00:00:59.040
Thus, in 1937, the
Tree of Life evolved

00:00:59.040 --> 00:01:03.360
to contain two large empires,
the eukaryotes with membrane

00:01:03.360 --> 00:01:07.020
bound nuclei and the
prokaryotes without.

00:01:07.020 --> 00:01:10.050
This paradigm, however,
resulted in some difficulty

00:01:10.050 --> 00:01:13.290
when it came to placing
prokaryotes on the tree.

00:01:13.290 --> 00:01:16.140
One rod-shaped microbe
is phenotypically hard

00:01:16.140 --> 00:01:18.270
to distinguish from another.

00:01:18.270 --> 00:01:23.340
Advancements in genetic
analysis, particularly 16s rRNA

00:01:23.340 --> 00:01:25.860
sequencing soon
toppled this tree

00:01:25.860 --> 00:01:28.650
when organisms traditionally
classed together

00:01:28.650 --> 00:01:31.530
as prokaryotes were
found to have genetically

00:01:31.530 --> 00:01:35.300
divergent evolutionary origins.

00:01:35.300 --> 00:01:38.990
So the Tree of Life
evolved once more in 1990.

00:01:38.990 --> 00:01:42.470
And the prokaryotes were
divided into two domains,

00:01:42.470 --> 00:01:46.040
giving us the three domains
of the modern Tree of Life,

00:01:46.040 --> 00:01:50.790
bacteria, archaea,
and eukaryotes.

00:01:50.790 --> 00:01:53.460
The first of these
domain's bacteria

00:01:53.460 --> 00:01:56.970
consists of unicellular
prokaryotic organisms that

00:01:56.970 --> 00:02:00.000
lack a membrane bound nucleus.

00:02:00.000 --> 00:02:03.180
The next domain
archaea is also made up

00:02:03.180 --> 00:02:06.750
of unicellular prokaryotic
organisms distinguished

00:02:06.750 --> 00:02:10.830
from bacteria by their
unique evolutionary history.

00:02:10.830 --> 00:02:15.000
Finally, the eukaryotes consist
of uni and multicellular

00:02:15.000 --> 00:02:18.840
organisms distinguished by
their membrane bound nucleus.

00:02:18.840 --> 00:02:23.160
This domain includes
fungi, plants, and animals.

00:02:23.160 --> 00:02:26.820
The evolutionary Tree of
Life, much like an actual tree

00:02:26.820 --> 00:02:28.500
is a living metaphor.

00:02:28.500 --> 00:02:31.290
And the classification
of many organisms,

00:02:31.290 --> 00:02:34.590
even the distinction between
archaea and bacteria,

00:02:34.590 --> 00:02:38.660
is often contested and
occasionally changed.

00:02:38.660 --> 00:02:40.000