Download Living Earth: A Short History of Life and Its Home PDF

TitleLiving Earth: A Short History of Life and Its Home
LanguageEnglish
File Size9.1 MB
Total Pages247
Document Text Contents
Page 2

LIVING EARTH

Page 123

REPRODUCTION AND DEAlli

this spirochaete basis. If this idea is correct (and many biologists do not accept
it), then it is to those symbiotically associated spirochaetes that we owe our
brains, and through them that we read this page.

During the aeons since these ancient symbiotic marriages, much of the
essential DNA originally in the chloroplasts and mitochondria seems to have
been moved from the organelles to the cell's nuc1eus, but enough still remains
to carry out the essential functions of the organelle. It is by studying this
remaining DNA that we can, for instance, deduce that the photosynthesizing
eukaryote is simply a new horne for the old cyanobacterium: the DNA in the
chloroplast is c10sely similar to that of the bacteria. By this symbiosis the
cyanobacteria have been able to colonize the land, create the Amazon forest
and persuade the authorities at Wimbledon to growa fine green patch of lawn
for tennis. New plants are simply old cyanobacteria writ large. Similarly, the
animal mitochondria that were once bacteria are now passed down from
generation to generation by reproducing animals. Each human being receives
slightly more from the mother than from the father, because the mitochondrial
information is purely maternal. For the symbiotic bacteria now incorporated in
eukaryotes, the arrangement has great advantages. Today, encapsulated
within the animals and plants, they walk the Earth, and inhabit the skies and
the ocean depths. We have gone to the Moon carrying with us in our guts our
microbial eubacterial and archaebacterial cousins. A human being is simply a
space suit for an assortment of bacteria. This, of course, is looking at matters
from the bacterial point of view: the arrangement is also to the benefit of the
eukaryotes, which could not learn the tricks such as photosynthesis afresh.

REPRODUCTION AND DEATH

Unlike bacteria, eukaryotes are created as male and female. Eukaryotes do not
necessarily need sex, yet they generally have it. Even relatively recently
evolved plants, such as tulips, dandelions and potatoes, can spread without
sex, and many animals can reproduce asexually. In theory, human beings too
can be c1oned. Sexual reproduction would appear to be disadvantageous to a
species: it means that part of the population, the male part, is unable to repro-
duce. In a competitive setting, this is very dangerous. Fewer offspring can be
born and the sexual organism runs the risk of falling behind in the reproductive
race.

In the longer run, sexual reproduction offers a different way of rearranging
the genetic material and thereby evolving new forms more efficiently than in
asexual reproduction. Sexual reproduction creates competition between males
and also provides a mechanism for correcting genetic errors in organisms. In
the short run, however, rapidly breeding asexual organisms appear to have the
advantage. Possibly, species that reproduce sexually may be sacrificing short-

111

Page 124

THE BIRTH OF THE EUKARYOTES

term advantage for long-term gain. It is almost as if in climbing to the evolu-
tionary heights each generation has to cross a dangerous ravine. Why on Earth
does sexual reproduction survive? The answer is not really yet known. Yet
many of the eukaryotes reproduce sexually, and many of them have roughly
equal numbers of males and females. In a few species, mostly vertebrate, there
is even the odd arrangement that males may match females in physical size and
status.

It is worth considering an analogy here, leaving science for a moment to con-
sider the evolutionary complexity of sex and death. Many years ago I studied
the introduction of advanced farming methods in a rural area in Africa. Most of
the people were poor, but one local farmer had become very successful. He had
managed to acquire no fewer than six wives. Each wife laboured in the fields for
him, generating income, and each wife produced children to her maximum bio-
logical capacity. The daughters so produced eventually went off in marriage,
the bride money paid to hirn by each new husband bringing in the price of ten
cows; the sons helped in the fields or sent back money from the towns. As he
became richer, he married more young wives, who produced more children to
make him richer, and so on. In contrast, his monogamous neighbours con-
tinued in poverty.

The man had become rich: for him life was pleasant, and he had had many
sons. Eventually, a few generations hence, the economy of the area will crash
as the population becomes too great for the local resources. But when it does,
even if many people starve to death, by then his descendants will greatly out-
number those of his near neighbours: however many people die, his
descendants maintain their advantage. After several cycles of boom and bust,
the neighbours will have either been exterminated or become polygamous
themselves in an effort to compete. Dnly the polygamous man passes on his
genes, eventually. The fitter genes dominate. The more wives per man, the
better to survive. The ratio of females to reproducing males rises. The
apparently logical end, of course, is to eliminate the man almost entirely.

Yet the elimination of the male has not happened in the eukaryotes. In our
human societies, in the West, the church has historically abhorred polygamy.
In economic terms, the nuclear family allows society to improve the individual
lot of the females and children, and in consequence, the collective lot. But such
altruism can be imposed on humanity only with the greatest difficulty: the
polygamous peasant plutocrat was not at all happy with the claims of his
church that he desist from the ways of Solomon, and listen to the preaching of
St Paul that women, different races, and even slaves have rights: 'There is
neither Jew, nor Greek, slave nor free, male nor female, for you are all one'.
Unlike humans, protozoa do not philosophize: why do simple organisms act
with apparent altruism, or interest in the future, if it means denying the interest
of the present generation?

A possible answer is that sexual reproduction was accidentally locked into

112

Page 246

INDEX

South Island, NZ 215
South Pole 146, 148, 192
South-East Asia 223
southern beech 204-215
Southern Ocean 215
Spenser, E. 68
sperm 157
sperm whale 169, 201
Sphenodon 163, 10.3
spiders 127, 139
spinifex texture 53
spirochaete 110-11, 115
sponges 118, 129, 8.7, 8.14b
spores 118, 141
squid 201
squirrel 9.10, 10.3, 11.3
Stahl, B. J. 205
Stanley, S. M. 145, 205
starfish 7.3
Steep Rock 87, 100, 103, 164,5.1,5.2

iron mine 59
Stegosaurus 171, 9.10, 10.2, 10.3, 10.4
sterns 140
Stenonychosaurus 180
Stenopterygius 10.3
Stephen's Island Wren 204
stereo vision 207
Stewart Island 204
stoats 204
stratopause 1.5
stratosphere 1.5
Strauss, R. 225
stromatolite 51, 52, 54-6, 58-9, 76-82, 86-7, 103-4,

121,5.1-5.6,6.3
sturgeon 8.8
subducting slab 1.11
subduction 20

zone 22,25,27,61,98,153,183,1.11,1.12
Suess, E. 147
sugar 31,42,87-8,90,2.1, 2.3
sulphate 54, 89-91
sulphide 87

ironstone 5.6
sulphur ·76, 89, 90

isotopes 86
sulphuric acid 8,1.4
Sun 4, 5, 6, 9, 10, 12-13, 15, 35, 43, 64, 89-90, 92,

94,96, 153, 192, 1.3
sunlight 164
Superior region 98-100, 106
supernova 4
surnames 76
suspension feeders 8.14b
Swart Krans 212, 218
Swaziland 49
swim bladder 137
symbiosis 84-5

figs 177

tadpoles 157
takahe 204
Tambora 184

236

Tanystrophaeus 9.10
tapirs 203
tarsiers 11.3
Tarsius 206, 208
Tasmania 148, 195-7, 204
Tasmanian Wolf 196
Taupo 184
Taylor, F. 147
Teaford, M. 218
tectonics 17
teeth, origin 137
temperature, end of Cretaceous 190
Terminal Cretaceous event 180-6
Terminal Perrnian event 181
terrnites 164
Texas 160
thecodont 10.3
therapsids 163
thermosphere 1.5
thorium, radioactive 5
Thunder Bay 98
thymine 31, 2.1
Tibet 98, 100, 153
TickelI, Sir Crispin 226
Tierra dei Fuego 182, 196
Tilapiamossambica 154
Titan 1.3
toad 71
tomato 193
tonalite 95
Tongariro Mt 225
tools 212-14
tooth 206
tortoises 158, 163, 190
trachodon 10.2
Trans-Hudson Orogen 100
transform fault 1.11
tree ferns 141, 176
tree of life 67-8,70, 74,4.1
tree shrews 206,9.10,11.3
trench 1.11
Triceratops 172, 9.10, 10.2, 10.3, 10.5
trilobites 127-8, 8.14c
trimerophytes 8.11
tritium 76
Triton 1.3
tropopause 1.5
troposphere 1.5
tsetse fly 163
tuatara 163, 185, 10.3, 10.8
tube worm 8.14d
turtle 163, 185,211,9.10,10.3

migration 158
Tyrannosaurs 127, 169, 172, 180, 201, 205, 10.2

uintatheres 11.3
ultraviolet light 9, 10, 35, 40, 85, 90, 120
Ulysses 15
unconformity 56, 3.6
undulipodia 110
ungulates 11.3
uniformitarianism 68

Page 247

INDEX

United States 126, 199
universal ancestor 39
universal genetic code 77
upper mantle 17,1.10,1.11
uracil 31, 2.1
Urals 148
uranium, radioactive decay 5
Uranus 1.3
USA 105
USSR 195-7

van Andel, T. J. 166
Venera space craft 8
Venus 4, 6, 8-10, 12-13, 16, 22, 25, 27, 29, 92, 94--6,

120,1.3, 1.4
Victoria Falls 191, 211
visible light 10
vision 206
voIcaniclastics 5.6
voIcanoes 142
von Damm, K. 46
von Neumann, J. 31, 36
Vonnegut, K. 13

Walker, A. 218
wallaby 195-7, 204-5
walruses 201, 11.3
wapiti 183, 204
Wapta Mt 127, 8.6
warm little pond 39, 40, 43
warm-blood 173
warthog 126
wasps 177
water 8,9,18,20,25

cycles 25, 27
vapour 15-16

Watson, A. 145
waves 142

237

weasels 183, 201, 204, 11.3
weather 164
Wegener, A. 147
West Indies 22
Western Australia 3, 47, 52, 99, 102-4, 106, 6.2
weta 165
whales 189, 199, 201, 211, 9.10, 11.3
wheat 136
Whittington, H. B. 129-34, 145
Williams, H. 6.1
Williston basin 101
wind 176
Windley, B. F. 105
Winnipeg 98, 148
Witwatersrand 80,101-2

goldfields 61
Wiwaxia 133, 8.7
wolverines 11.3
wolves 11.3
wombats, giant 219
wood 140-1
woolly mammoth 215
woolly rhino 220
worms 118-21, 129--30, 8.7
Wynberg 128
Wyoming 100

xenon 6

yeast 7.3
yellow wood tree 176

Zambesi valley 135
zebra 189, 199
zeolite 42,44-5,2.4
Zimbabwe 49, 51, 53-4, 58, 99, 101, 106, 155, 177,

197,223,3.1,3.2,5.3,5.4
zircon 3, 47
zooplankton 115, 8.14b

Similer Documents